Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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- . . _ DESCRIPTION _ -. . _ _ .
VIDEO PROCESSING METHOD AND APPARATUS
FIELD OF THE INVENTION
This invention relates to video signals and, more
particularly, to apparatus_and method for encoding and
decoding video signals for-use in television-'and in high
definition television systems as well as in other
applications including storage and/or transmission, over any
suitable medium, of moving images, or combinations of moving
and still images, in a form that requires reduced storage
capacity and/or reduced bandwidth channels. Some of the
techniques hereof can be employed, for example, for
transmitting through the air or through conducting or optical
cable, a plurality of video signals using only the bandwidth
generally allocated to a single video signal, and with little
or no perceived degradation of image quality. Some of the
techniques hereof can be employed, for example, in so-called
"compatible" high definition television approaches, as in
so-called "simulcast" approaches wherein independent high
definition television signal is sent simultaneously with a
conventional transmission of the same program information.
Some of the techniques hereof can also be employed in
so-called "enhanced definition" approaches that send picture
enhancement information (but less than the information needed
for full high definition performance) on the same channel
with a conventional television program.
BACKGROUND OF THE INVENTION
Available spectrum is becoming increasingly burdened by
ever greater demand for video information channels.
Traditional airwave spectral space has been crowded for many
years, and burgeoning video programming for such applications
as home cable, teleconferencing, picture phones; and computer
video transmission has now crowded conductive and optical
cables, phone lines, and sattelite communication channels.
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The desirability of techniques for increasing the amount of
video information that can be sent- over these transmission
media is evident. Also, as more video information-is stored,
it is desirable to develop techniques that increase the
amount of video that can be stored in a given storage size.
As high definition television (HDTV) becomes more
prevalent, improved systems are,needed for transmission and
reception of the additional information required for -
presenting HDTV images. Any-new service which provides
higher definition television than is conventionally broadcast
(i.e., more elements per line and lines per frame, and thus a
wider bandwidth necessary for transmission) should serve
existing home television receivers with essentially all the
picture attributes and quality of which the receivers are
capable. Also, receivers designed for new (high definition)
service, should be capable of operating using the
pre-existing transmissions and derive from them a result not
inferior to that provided by pre-existing receivers.
A variety of HDTV schemes have been proposed. In U.S.
Patent No.s 4,517,597, 4,628,344, 4,652,909, 4,701,783, and
4,800,426, assigned to the same assignee as the present
application, as well as in the publication "HDTV Compatible
Transmission System", W.E. Glenn, National Association of
Broadcasters, April, 1986, there is disclosed an HDTV system
that utilizes an augmentation approach which permits
compatible transmission of HDTV. A separate auxiliary or
"augmentation" channel is used to send picture detail
information that augments conventionally received television
information to obtain high definition performance. The
disclosed techniques also have application to video bandwidth
compression and to reducing video storage capacity.
As described in the referenced patents and publication,
an electronic video signal (e.g. a television signal) can be
encoded at reduced bandwidth by lowering the frame refresh
rate of the high spatial. frequency components, while
maintaining the frame- refresh rate of at least a portion of
the low spatial frequency components_at the standard rate.
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If done in a. specified. manner. this: will: not- cause- substantial
degradation inthe..ultimately displayed.image,-=-.since humam -
vision cannot perceive changes-in high spatial- resolution
information at as.fast a rate as it can perceive changes in w
low spatial resolution information. Accordingly; as has been
previously set forth.,-an"electronic video encoding and
decoding system can be devised which takes advantage of this,
and other, characteristics of human vision by encoding higher
spatial resolution video components to be at a temporal
information rate.which; approximately corresponds to the
highest rate actually: perceived by human vision for such
components; thereby eliminating the need to encode these
components at a higher rate, which inherently wastes
bandwidth. Also, as shown in referenced patent and
publication, the low spatial resolution information can be
generated in a form which is compatible with standard
television video, for example NTSC video used in the U.S. It
has also been recognized that a number of frequency
components can be transmitted at specified rates [see e.g.
W.F. Schreiber et al., Reliable EDT~7/HDTV Transmission In Low
Quality Analog Channels, SMPTE Journal, July 1989, and the
abovereferenced patents of the present assignee], with
components selected according to degree of motion in order to
have higher spatial resolution in scenes with. little motion
and higher temporal resolution in scenes with a-great deal of
motion.
Fig. 1 illustrates a compatible high definition
television transmission, and receiving system of the general
type described in the above-referenced patents and
publication. A transmitter 200 includes NTSC processing
circuitry 210 which processes television signals from a
source such as a television camera system (not shown) or a
video recording system (not shown). The circuitry 210 is
coupled to transmitting circuitry.215, which typically
includes modulation circuitry and other suitable circuitry .
for producing a signal to be transmitted over.a'standard NTSC
channel. The television_signals from the television camera
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system-_or:_video:recorder (which is- assumed-to have a high
definition-_video_capabi_lity) are also processed by high
definition television (HDTV) processing circuitry 260 which
produces detail signals that can be utilized to enhance
conventional television signals to obtain HDTV signals, as
described in, the abovereferenced patents and publication.
(As further-described in the referenced U.S. Patent No.
4,652,909,. the-detail signal can be obtained from a separate
camera.] The detail-signals are coupled to further circuitry
275, which transmits the detail signal over a second
(auxiliary) channel that is typically not adjacent to the
(main) NTSC channel used for transmission of the standard
portion of the television information. The NTSC signal is
received by receivers such as receiver 310 which has only a
capability of producing a television picture at substantially
conventional resolution e.g. conventional display 315.
Receivers such as receiver 360, which have a capability for
receiving, processing, and displaying high definition
television signals, receive both the main channel carrying
the NTSC signal and the auxiliary channel carrying the detail
signals to be used for augmentation of the NTSC video signal
so as to produce a high definition television signal for
display on an HDTV display 365.
In the referenced patents and publication, the spatial
detail is transmitted at a relatively slow frame rate, such
as 15 or 7.5 frames per second. "]utter" (jerky edge motion)
was observed when the detail frame rate was reduced too far.
This artifact constrains the augmentation channel bandwidth
to be larger than would otherwise be indicated by
psychophysical studies. Camera lag, caused by the
integration of image energy on the face of the camera tube,
which attenuates detail in moving areas of the picture, can
be exploited to reduce jutter, but some reduction in image
detail can be observed in moving objects when they are
visually tracked. .It is among the objects of the present
invention to provide improvements in performance and in
bandwidth _ compression with respect to the techniques
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described above and-with respect-to~other prior artw -
techniques. It-is-alsoy~among--the--objects hereof to provide:
such improvements-in a. system_thatcan be made compatible
with existing or_future:.--television standards (for example, '
NTSC, or other standards such as PAL or SECAM).
As further background tovthe.invention, reference can be
made to the following U.S.-Patents which relate to~
compression, transmission and/or other processing of video
signals and/or still picture information: - U.S. Patent
4,196,448, 4,210,931, 4,224,678; 4;302;775, 4,394,774;
4,541,012, 4,605,952, 4,630,099; 4,661,862; 4,672,425,
4,675,733, 4,675,750, 4,729,012, 4,774,562, 4,780,761,
4,791,598, 4,807,029, 4,821,119,.4,845,562, 4,851,906,
4,870,489 and 4,873,573.
The FCC recently announced that it prefers planned
terrestrial HDTV transmission in the U.S. to be broadcast
using a simulcast format: i.e., with the same program content
sent simultaneously both a conventional television channel and
a separate HDTV channel. It has been anticipated that, in
time, television viewers will replace standard NTSC receivers
with high definition sets, thereby allowing the present NTSC
channels to eventually be reassigned for other application.
In order for this concept to work, however, viewers must be
motivated to purchase receivers designed to accept this new
format. Even when wide-screen HDTV becomes available, a
significant demand will always exist for smaller-screen
receivers. The image quality of small screen-size television
receivers is generally not limited by transmission
considerations, but by human visual acuity. The optimum
viewing distance for popular 19-20" conventional receiver, for
example, is between six and seven feet. A similar screen-size
HDTV receiver has an optimum viewing distance of about three
feet; clearly impractical in most viewing situations:- The
goal of abandoning the conventional NTSC channels in the
foreseeable future may be impractical because there will
always be a.consumer demand,for inexpensive smaller screen
television sets.
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It is also.among.the.objects of the present-invention-to -
provide improvements in encoding and decoding of video
information which addresses the described problems and
limitations of the prior: art, achieves substantial bandwidth
savings, increases the efficiency of video transmission and
storage, and provides a capability for higher definition
television transmission in the bandwidth of a single
conventional television channel. It is also among the
objects of the present invention to provide a technique
whereby two video signals, representative of different images
can be transmitted using only the bandwidth generally
allocated to a single video signal, with little or no
perceived degradation of image quality. It is also among the
objects of the present invention to provide a method for
broadcasting video signals with improved interference
immunity.
SUMMARY OF THE INVENTION
A method and an apparatus are set forth for encoding and
decoding video to-achieve bandwidth compression. In one form
of the invention, two video signals, representative of
different images, can be transmitted using only the bandwidth
generally allocated to a single video signal, with little or
no perceived degradation of image quality. In another form of
the invention, motion indicative signals are used in a
technique that dynamically modifies the frequency band
information to be stored and/or transmitted.
Further features and advantages of the invention will
become more readily apparent from the following detailed
description when taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a simplified block diagram of a prior
compatible high definition television system.
Fig. 2 is a polar plot illustrating data that measures
the oblique effect.
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Figs. 3A,.. 3B and_3C-.-respectively--illustrate- cardinal
sampling, quincunx sampling,.and quincunx sampling with -
reduced sampling rate. --. ~- -
Figs 4A, 4B and.4C respectively illustrate spectra for
the Fig. 3A, 3B and 3C situations. - -
Fig s 5 and 6 illustrate spectra referred-to in the
description. ~- _
Fig. 7 illustrates the four quadrant pass band of a
two-dimensional diagonal filter having its vertical and
horizontal cutoff frequencies at half the video sampling
rate.
Fig. 8 is a block diagram of an embodiment of an encoder
and encoding method in accordance with a form of the
invention.
Fig. 9 illustrates an example of the coefficients of a
9x7 filter kernel array.
Fig. 10 is a block diagram of circuit which can be
utilized to implement two-dimensional convolution with a
filter kernel.
Fig. 11 illustrates an example of two-dimensional
spectrum folding around a diagonal which occurs as a result
of a two-dimensional image modulating a two-dimensional
subcarrier.
Fig s 12A and 12B respectively show a pixel array before
and after two-dimensional modulation.
Fig. 13 illustrates a circuit for implementing two-
dimensional modulation.
Fig. 14 shows a block diagram of an embodiment of a
decoder and decoding method which can be utilized to recover
signals encoded in accordance with a form of the invention.
Fig s 15A, 15B, 15C 15D and 15E shown illustrative
spectra.
Fig. 16 is a block diagram of an embodiment of an
encoder and encoding method in accordance with another form
of the invention. ~ ~ _
Fig. l7 is:a diagram-of-a decimator which can be
utilized in an embodiment of the invention.
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Fig. l8,is.a block.:,diagram._of._an--embodiment of a decoder
and decoding method which can be_utilized to decode the
encoded signals of a form of the invention. --
Fig. 19 is a diagram of a zero padder which can be
utilized in embodiments of the invention.
Fig. 20.is a block diagram of an embodiment of an
encoder and encoding method in accordance with another form
of the invention. -
Fig. 21 is a block diagram of an embodiment of a decoder
and decoding method which can be utilized to decode signals
encoded in accordance with a further form of the invention.
Fig. 22 is a block diagram of an embodiment of a high-
definition television system and method in accordance with a
further form of the invention.
Fig. 23 illustrates a further form of the invention that
is used to minimize interference between transmitted video
signals.
Fig s 24 and 25 illustrate exemplary band divisions of
the Fig. 6 spectrum.
Fig. 26 is a block diagram of an encoder in accordance
with an embodiment of the invention, and which can be used to
practice an embodiment of method of the invention.
Fig. 27 is a block diagram of a system for encoder scan
conversion.
Fig. 28 is a block diagram of a portion of the encoder of
the Fig. 26 embodiment.
Fig. 29 is a flow diagram a routine for controlling the
tile control processor of Fig. 28.
Fig. 30 is a block diagram of an embodiment of the motion
detection circuit of Fig. 28.
Fig. 31 is a block diagram of a decoder in accordance
with an embodiment of the invention and which can be utilized
to practice an embodiment of the disclosed decoding method.
Fig. 32, which includes Fig s 32A and 32B placed one
below another, is a flow diagram of the routine for
controlling the augmentation input processor of.the Fig. 31
embodiment.
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Figs 33 and 34;.are-flow diagrams of the routine for--
implementing the spectral-to-detail converter control --
processor of the Fig. 31 embodiment.'- w
Fig. 35 is a block diagram of a fifo circuit utilized in
the Fig. 31 embodiment.
DETAILED DESCRIPTION
Subjective vision. studies have indicated that perceived
resolution is anisotropic (not equally precise in all
directions). The eye is more sensitive to detail along the
horizontal and vertical~axes than to that along diagonals:
[See, for example, W.E. Glenn et al., "Imaging System Design
Based On Psychophysical Data," Proc. of the SID, Vol 26/1, pp.
71-78, Jan. (1985); NYIT STRC "Visual Psychophysical Factors
as Applicable to the Design and Development of Video Systems
for Use in Space, Final Report," NASA Report, May (1989); G.C.
Higgins et al., "Variation of Visual Acuity with Various
Test-Object Orientations and Viewing Conditions," J. Opt.
Soc. Am. 40, pp. 135-137 (1950); F.W. Campbell et al.,
"Orientational Selectivity of the Human Visual System," J.
Physiol., 187, pp. 437-445, (1966); and S. Appelle,
"Perception and Discrimination as a Function of Stimulus '
Orientation: The "Oblique Effect" in Man and Animals,"
Psychological Bulletin, Vol. 78, No. 4, pp. 266-27B, (1972).)
Fig. 2 illustrates this oblique effect, plotted in polar form,
as characterized by various researchers. While results differ
somewhat due to the different types of testing employed, the
curves of subjective resolution have a similar shape and
diverge from the isotropic resolution shown by the outer
circle. It is known that bandwidth and display element
density can be reduced by taking advantage of the anisotropic
spatial response characteristics of the visual system. Fig s
3A, 3B and 3C respectively illustrate cardinal sampling,
quincunx (or diagonal) sampling, and quincunx sampling with
reduced sampling rate. Fig s 4A, 4B and 4C show the
respective discrete spectra for-the sampling of Fig s 3A, 3B
and 3c, where fs =.-1/D. The quincunx sampling shown in Fi g s
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3B and 3C results in the rotation of the spectral coordinate
axes by 45 degrees [see, for. example,.R.C.- Gonzales et al.,
Digital Image Processing, Reading Mass., Addison-Wesley
(1987); E. Dubois et al.,"Three-Dimensional spectrum and
Procession of Digital NTSC Color Signals," SMPTE Journal, pp.
372-378, April (1982); and B. Wendland et al. "On Picture
Quality of Some Television Signal Processing Techniques,"
SMPTE Journal, pp. 915-922, Oct., (1984)), thereby more
closely matching the characteristics of vision. This method
can be used to reduce the information content by a factor of
two without degradation in perceived image quality. Half tone
prints and, more recently, CCD cameras and LCD displays are
successfully utilizing this technique. Some of the systems
described in the patents referenced in the Background portion
hereof utilized quincunx sampling to reduce the sampling rate,
and therefore the augmentation bandwidth, by a factor of two.
In an embodiment described below, information content is
reduced by eliminating high diagonal frequency components
approximately to the upper right of the diagonal line 5 in the
discrete spectral domain illustrated in Fig. 5. The NTSC
luminance spectrum is illustrated approximately in the lower
lefthand box of Fig. 5. In a subsequently described
embodiment, for an augmentation system wherein the NTSC
spectral portion is available from a conventional channel,
the approximate remaining spectrum used for transmission on
the augmentation channel is shown in the shaded region of Fig.
6.
A low-pass filter can be used to restrict the frequency
components of a cardinally sampled image to the region within
the diamond-shaped perceptivity curve of Fig. 2. A television
viewer, positioned at the most favorable viewing distance
(roughly six screen heights for conventional NTSC 525 line
video), is not able to resolve the (vertical) video raster,
yet is still able to appreciate image detail. Figure 7 shows
the four quadrant pass-band of a two-dimensional diagonal
filter having both its vertical and horizontal cutoff
frequencies set to one.-half the video sample rate (for
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example, one-half the vertical sampling rate): One-half the
total spectral area is passed by this filters The effective
two-dimensional bandwidth for images matched to the
characteristics of the human visual system is only one-half of
that created by cardinal sampling. In accordance with a
feature of the present invention, useful video information is
two-dimensionally modulated so as to be positioned in the
shaded portion of Fig. 7; i.e.,- into a spectral region that
has been effectively unused and generally wasted in prior art
systems . In an embodiment hereof, two different television
images, for example, can be encoded on a single transmission
channel by effectively placing one in each of the two distinct
spectral regions. Applicant has discovered that each
television picture can maintain substantially the full
subjective resolution found in the original, and is completely
separable from the other television picture.
Referring to Fig. 8, there is shown a block diagram of an
apparatus in accordance with an embodiment of first form of
the invention, and which can be used to practice a form of
the method of the invention. Two electronic video signals
are produced, as represented by the blocks 810 and 850,
respectively. The electronic video signals may be generated
by any suitable means, for example by video cameras, video
storage, graphics or animation generators, or medical or
other imagers, etc. It will be understood that the blocks
810 and 850 may represent respectively different types of
sources of electronic video signals. As an illustrative
example, it can be assumed that the blocks 810 and 850
represent electronic video camera systems directed at
different scenes. As described hereinbelow, the signals can
also be representative of different components of the same
image. Also, it will become understood that the techniques
are applicable to various formats of electronic video signals
and to conventional as well as low or high definition video:
An example is initially set forth in terms of a monochrome
video, signal having conventional television resolution,
although the techniques hereof are also generally acceptable
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to color video_ signals::. -. .. ._ _.. _ _ _ .._ _ _ _ _ _ _... . .
The outputs of video signal sources 810 and 850 are- ----
respectively coupled to--low pass:filters 815 and-855 (see r
also two-dimensional spectra 815A and 855A), and then to
analog-to-digital converters 820 and 860. The analog-to-
digital converters can be operated at any suitable clock
rate, in known fashion, to obtain frames of digital pixels
which are stored-in digital buffers 821 and 861,
respectively. The buffers may be frame buffers. or portions
thereof. Each pixel-of each frame can have a luminance value
conventionally represented by an n-bit digital word.
The outputs of frame buffers 821 and 861 are
respectively coupled to two-dimensional diagonal low-pass
filters 825 and 865. Each of these filters is operative to
remove high frequency two-dimensional diagonal frequency
components from the frames of digitized video signal. For
example, for the approximately square spectrum of the first
quadrant Fig. 7, the filtering of the present embodiment will
preferably result in a spectrum having an approximately
triangular shape as in the unshaded region in Fig. 7 (see
also the sketches 825A and 865A). It will be understood,
however, that the line joining the highest passed vertical
and horizontal frequencies [(f~~z = constant] can generally be
considered as a boundary. As noted in conjunction with the
description of. Fig. 2, there are investigators who have
determined that even some frequencies within the indicated
triangular region will be substantially attenuated by the
human visual system. The precise shape of the filter can be
determined from present and/or future studies on the human
visual system, and/or can be adjusted empirically.
The two-dimensional diagonal low-pass filter (825 and
865) can be implemented by any suitable technique. For
example, a commercial programmable filter kernel can be
utilized.to obtain the desired filtering function. Fig. 9
illustrates an example of the coefficients of a 9x7 filter
kernel array that can be utilized to implement two-dimensional
diagonal.low-pass filtering. The filter kernel can be applied
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by convolving the array with the frame of pixels to be
filtered. Techniques-for--implementation-of the filtering
process, are known in the art. Fig. l0 shoias a block diagram
of a circuit which can be utilized to implement
two-dimensional convolution,-and which can be employed, with
appropriate weighting coefficients, in the present embodiment
to implement a two-dimensional diagonal low-pass filter. In
the circuit of Fig. 10,_.an array of coefficients kij, are
applied to an (m)x(n) moving group of pixels by using m line
delays 1020 and n pixel delays which are indicated in Fig. 10
by representative register rows 1025, each of which has
individual stages with respective one pixel delays. Shift
registers or FIFOs may be used for this purpose. Each pixel
and delayed pixel is multiplied by a coefficient, klj, with the
coefficient values being implemented by applying corresponding
signal levels to the multipliers 1050. The coefficients can
be in accordance with the selected array for a particular
filter kernel, for example the array illustrated in Fig. 9.
The outputs of multipliers 1050 are summed by a summing
circuit 1080 which produces each convolved output signal as
the array "moves" over the frame. It will be understood that
other filter implementations, including commercially available
chips, can be utilized, if desired, and that end conditions
can be handled by techniques known in the art.
Referring again to Fig. 8, the output of two-dimensional
diagonal low-pass filter 825 is coupled to one input of -
summing circuit 880. The output of two-dimensional diagonal
low-pass filter 870 is coupled to a two-dimensional modulator
870, which serves to fold the spectrum of the filtered signal
into the spectral space normally occupied by the high
frequency diagonal components. Fig. 11 illustrates an example
of the two-dimensional spectrum folding which occurs when a
two-dimensional image modulates a two-dimensional subcarrier
having (in this case) a horizontal frequency of half the
sampling rate and a vertical frequency of half the sampling
rate. In general, the image spectrum will be folded around
the diagonal demarcation line and reversed'so that high
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frequency horizontal components:-of the original image become
high frequency.vertical components and vice-versa as shown in
Fig. 11. A constant gray-level (dc) on the encoded image will
then appear as the highest possible frequency which can be
represented with the sampling. parameters, fs/2, fs/2. In other
words, the spectral location (0,0), after such two-dimensional
modulation, will be at (fs/2, fs/2) and constant intensity.
level will generally appear as a high frequency checkerboard
pattern. [For this modulation in the image brightness domain,
being modulated in this case as brightly above the average
gray level as below it,- the entire image content would be lost
and appear as a blank gray screen to a viewer more than six
screen heights from the display, since the spectral content
is outside the range of human perceptivity, i.e. the human
visual system would act as a diagonal low-pass filter.] The
spectral location (0, fx), after such two-dimensional
modulation, will be at (fH/2, fs/2-fX), and so on. The
two-dimensional modulation to achieve folding around the
diagonal can be implemented by reversing the polarity of every
other pixel on every line, with the polarity order reversed
every other line, as illustrated in Fig s 12A and 12B. Fig.
12A shows a pixel array before two-dimensional modulation on
the two-dimensional subcarrier, and Fig. 12B shows the pixel
array after such modulation. Fig. 13 illustrates a circuit
for implementing this modulation. A multiplexes 1350
receives, at one input, the pixel output of two-dimensional
filter 865 and, at another input, the pixel output inverted by
inverter 1310. The modulator receives pixel and line
indications and alternates its input line selection sequence
in accordance with the polarity sequence shown in Fig. 12B.
The encoded output of summing circuit 880 contains video
signals representative of both images (see two-dimensional
spectral sketch 880A which denotes the respective video signal
spectra as 1 and 2), can be stored and/or transmitted, as
represented by the block 890.
Referring to Fig. 14, there is shown a block diagram of a
decoder which can be utilized to recover and record and/or
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display the encoded video signals: The block 1410-represents
the receiving of the encoded signal or the reading thereof
from storage. The two-dimensional frequency spectrum is shown
in the sketch at 1410A. An optional pixel storage-buffer 1415
can be used to store frames of information or pprtions
thereof. The output of buffer 1415 is coupled to a
two-dimensional modulator which can operate in the same manner
as modulator 865 (Fig..8), as illustrated in conjunction with
Fig s 11-13. The previously described spectrum folding
reverses the spectral positions of the video signals. The
output of modulator 1450 is coupled to a two-dimensional
diagonal low-pass filter 1470, which may again be of the type
illustrated in conjunction with Fig s 9-10. The output of
buffer 1415 is also coupled to such a filter (1420). The
respective outputs of two-dimensional low-pass filters 1420
and 1470 are coupled to digital-to-analog converters 1425 and
1475, and then to analog (horizontal) low-pass filters 1430
and 1480. The output analog video signals can be recorded
and/or displayed, as represented by the blocks 1435 and 1490,
respectively. In operation, it is seen that the
two-dimensional modulator operates to "reverse" the spectral
locations of the signals identified as "1" and "2" (see sketch
1450A). The filters 1420 and 1470 can then be utilized to
filter undesired spectral components and obtain the
respective separated video signals (see also sketches 1420A
and 1470A). After conversion to analog form and suitable
low-pass filtering, the recovered signals can be recorded
and/or displayed, as desired.
In accordance with a further form of the invention, the
size of an image may be reduced, or squeezed, by sub-sampling
after first filtering to remove frequencies which would
otherwise cause aliasing. As will be described, an image can
be reduced to half its original size by throwing away, or
decimating, alternate pixels horizontally and vertically.
Spatial decimation can also be used to reduce the data content
and associated transmission bandwidth of non-squeezed images
without substantially degrading-the subjective resolution.
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Before considering two-dimensional decimation, it is helpful
to examine-the effects of one-dimensional decimation. If it
is assumed that a continuous analog signal is sampled using a
digitizer which has an infinitely small sampling aperture,
the digitized input can be considered as a continuous analog
signal multiplied by a series of impulses spaced T seconds
s
apart. The sampled spectrum consists of the original analog
spectrum convolved with spectral impulses located at of where
S
fs=1/TS. Repetitions of the analog spectrum will thus be
centered about integral multiples of the sampling frequency as
shown in Fig. 15A. No aliasing will occur if the analog
baseband spectrum is restricted to frequencies less than f /2
prior to sampling. Assume, now, that even and odd samples are
separated using the following even and odd decimating
functions:
DEC - (1/2)[I + cos2pi*(fs/2)(x/fs)J
even
- (1/2)[1 + cos(pi*x)J
DECoaa - (1/2)[1 - cos(pi*x)J
where x = integral sample number
Applying DECe~en to the data set will force the odd data
elements to zero while DECoaa will force the even elements to
0. The spectrum of an evenly decimated image is obtained by
convolving the sampled spectrum with the spectrum of DEC
even
Fig. 15B shows that decimation causes another repetition of
the analog spectrum to be created about fB/2. Aliasing will
occur for frequencies greater than fs/4. DEC oaa will create a
similar spectrum, but the aliased components will be inverted
with the respect to the aliased spectra from DEC When the
even
odd and even components are added, the unaliased original
components add, but aliased components cancel, leaving the
original spectrum. While this result is interesting, it is
of little practical value in one dimension: the same result
is obtained by sampling the analog input at f$/2.
Spatial decimation, however, does not lead to the
trivial result encountered in one dimension, provided a
diagonal decimating pattern is used. A diagonal decimator
masks an image with a checkerboard pattern of (e. g. black)
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dots. The even decimator can be represented as:
DECdiag = (1/2)[1 + cos(pi*x)cos(pi*y)]
The spectrum of the decimator is composed of two
frequencies, one-at DC:(0,0), the other at half the -
horizontal and vertical sampling rates (fh/2,f~/2). It is
analogous to the one-dimensional decimation spectrum except
that frequencies are two-dimensional. An image to be
decimated can be first passed through a two-dimensional
diagonal pre-filter of the type previously described. The
decimated spectrum is obtained by convolving the filtered-
image spectrum with the spectrum of the decimator. The
original filtered spectrum is repeated about multiples of the
decimating frequency, i.e.
(2m+1)f8/2,(2n+1)fs/2 for all m and n
a portion of which is shown in Fig. 15C. Passing the
decimated image through another diagonal filter regenerates
the undecimated image without degrading the image quality.
To summarize the foregoing discussion, when a diagonally
pre-filtered image is spatially decimated diagonally the
spectral components introduced by the decimation process do
not extend into the original spectral region, and hence may
be removed by filtering.
Diagonally decimated images contain half the number of
pixels per line of cardinally sampled images. The time
.Zecessary to send a line of video can be reduced by half if
the bandwidth is maintained constant, so that the image will
be squeezed horizontally: The second half of each video line
may then be used for other purposes, such as carrying a
second image or carrying high definition components of the
basic image. Squeezed images can be reconstructed at the
receiver by reinserting the zeros created by the decimator
and passing it through a two-dimensional low-pass filter.
Fig. 15D is a representation of a two-dimensional
frequency spectrum of a decimated image which is composed of
repetitions of the cardinally-sampled spectrum about
multiples of.the decimating frequency, i.e, at
( 2m+1 ) f~~zo~eal/2 ~ ( 2n+1 ) f"~rc~c~l/2 _ .
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for all integral values of m and- n: ---w
Frequency-aliasing will occur if the image is not
properly pre-filtered and likewise, if the zero-padded
reconstruction is;not adequately post-filtered. Fig. 15E
shows that a two-dimensional filter with a diamond-shaped
pass-band that can be used for both the pre- and post-
filter. It removes only those spectral components outside
the sensitivity range of the human visual system. Pictures
with the same subjective quality of the original image can,
therefore, be reconstructed from a diagonally-decimated
image.
Referring to Fig. 16, there is shown a block diagram of
an embodiment of a form of the invention which utilizes
principles just set forth. Two sources of video signal, 1610
and 1650 are provided, as previously described in conjunction
with the description of Fig. 8. The signals are horizontally
low-pass filtered and analog-to-digital converter as
represented by the blocks 1615, 1620 and 1655, 1660,
respectively (see also sketches 1615A and 1655A). The
outputs of the analog-to-digital converters are respectively
two-dimensionally low-pass filtered, such as in the manner
previously described, as represented by the blocks 1625 and
1665. The resultant respective two-dimensional spectra are
represented in sketches 1625A and 1665A. The filtered images
are then decimated, in the manner previously described, as
represented by the blocks 1630 and 1670, respectively. The
pattern of pixels selected by the decimators are illustrated
in the diagrams 1631 and 1671, respectively. In the present
embodiment, only the selected alternate pixels (as
illustrated) are passed by the decimators, and this can be
implemented, for example, by using voltage-controlled gates
as illustrated in Fig. 17. In particular, line and pixel
information provided to the controlled gate determines
whether the pixel is passed by the decimator. Alternatively,
a flip-flop, which is set to a different initial status each
line, could be utilized. The outputs of decimators 1630 and
1670 are respectively coupled to time base compressors 1635
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and 1675 which operate to compress each line of pixels into
respective halves of the-original line time. Time base
correction is very. well known in the art, and any suitable
time base compressor can be utilized for this purpose. The
compressed two- dimensional spectra of the resultant signals
are represented in sketches 1635A and 1675A, respectively.
It is seen that the horizontal component is doubled. A
multiplexes 1690 is then utilized to combine the signals
during successive time slots, as illustrated in the diagram
1690A. The resultant signal can be stored and/or
transmitted, as represented by the block 1695.
Referring to Fig. 18, there is shown a block diagram of
an embodiment of a decoder which can be: utilized to decode
the encoded video signals of the Fig. 16 circuit. The block
1810 represents the receiving or the reading from storage of
the encoded signal. A demultiplexer 1815 is utilized to
separate the signals in the two time slots of each line, and
the demultiplexer outputs are respectively coupled to time
base correction circuits 1820 and 1850, respectively, which
perform the converse of the operations that were performed by
corresponding time base correctors 1635 and 1675 in the
encoder. The outputs of the time base correctors are
respectively coupled to pixel storage buffers 1825 and 1855,
and these may comprise, for example, half-frame stores. The
outputs of the buffers are respectively coupled to zero
padders 1830 and 1860 which operate to insert zeros at
diagonally alternating pixel positions, as represented in the
diagrams 1830A and 1860A, respectively. A circuit which can
be utilized to implement the padders is illustrated in Fig.
19. In particular, a multiplexes can be utilized which
receives, as inputs, the pixels output from the buffers (1825
or 1855) and a signal representative of a zero level.
Selection of the value to be passed by the padder will depend
on the line and pixel information input to the multiplexes,
in accordance with the illustrated alternating pattern. The
outputs of padders 1830 and 1860 are respectively coupled to
two-dimensional diagonal low-pass filters 1835 and 1865,
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respectively, which, as previously described, operate to
remove the aliasing components. The outputs of the filters
are coupled to digital-to-analog converters 1840 and 1870,
respectively, and then can be analog low-pass filtered
(horizontally), if desired, and displayed and/or recorded, as
represented by the blocks 1845 and 1875, respectively.
Referring to Fig. 20,.there is shown an embodiment of a
form of the invention wherein two video signals can be
combined. on a single channel with reduced bandwidth
requirement, analog processing being utilized in this
embodiment. As before, two video input signals are received
from video signal sources (2010 and 2050). The present
invention (in both digital and analog processing
implementations) may sometimes be practiced without initial
two-dimensional diagonal low-pass filtering, since most
natural images have little spectral energy to begin with in
the high diagonal frequency region of the spectrum. The
embodiment of Fig. 20 is an example of processing without
such prefiltering. In the embodiment of Fig. 20 it is
assumed, also as an example, that the video comprises
interlaced video. Also in this embodiment, the two-
dimensional modulation is implemented by separate vertical
and horizontal modulation. In particular, the block 2020
represents the vertical modulation. For an interlaced
display, alternate lines occur in successive fields, so
vertical modulation can be obtained by inverting during every
other field. A multiplexes 2021, which is controlled on a
line 2021B by a signal derived from field synchronization,
selects either the video received via an amplifier 2022 or
the video received via inverting amplifier 2023. The
resultant "alternate line inverted" signal is used to drive a
double balanced modulator (which implements the horizontal
modulation component), the mixing frequency (fm) of which,
received on line 2030B, is selected as the maximum pass-band
frequency, for example 4.2 MHz. In order to maintain the
unipolar nature of the video, a bias equal to half the
maximum unipolar video level. is subtracted prior to encoding
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by difference-.circuit 2005; and is then reinserted after the
modulation process, by summing circuit '2050. The modulated
and unmodulated video_signals are added by summing circuit
2060, low-pass-filtered (block 2070) and recorded and/or
transmitted (block 2080).
Referring to Fig. 21, after storage and/or transmission,
the combined signal:is-received and/or read from storage
(block 2110), and can be decoded to recover the original
signals. The combined signal is coupled to a two-dimensional
diagonal filter 2120 to obtain the low two-dimensional
diagonal frequencies on a line 2020C, and the high
two-dimensional frequencies on a line 2020B. The diagonal
filtering may be implemented in analog fashion or by
converting to digital form, separating as above, and
reconverting. The signal 2120C can be recorded and/or
displayed, as represented by block 2180. The signal 2120B is
two-dimensionally modulated, in one-dimensional stages
analogous to the encoding process of Fig. 20. In particular,
a multiplexes 2140, which is controlled on a line 2140B by a
signal derived from field synchronization, selects either the
output of an amplifier 2130 or of inverting amplifier 2135.
The result is then passed through a double-balanced mixer 2150
which receives, as its other input, a signal at the same
frequency as that used at the transmitter; i.e., a 4.2 MHz
signal in this example. Bias can be suitably added by
summing circuit 2160 and the resultant signal stored and/or
displayed, as represented by block 2170.
The high frequency diagonal portion of the
two-dimensional spectrum can also be utilized to carry
components of the primary image (for example, high definition
components, color components, additional image area to modify
aspect ratio or for other purposes, etc.), or to carry other
information such as data, still pictures, audio, etc. Fig. 22
is a block diagram of a high definition television system
which two-dimensionally modulates the high definition
television system which two-dimensionally modulates the high
definition components into the high frequency two-dimensional
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22
diagonal region. A source of high definition (which can be
considered as. encompassing-a signal with substantially higher
definition than current conventional television video) 2205 is
provided. The output thereof, is coupled to the positive input
of a difference circuit 2207, and to a block 2210 which
represents two-dimensional low-pass diagonal filtering of the
high-definition video.signal. This filtering may be
implemented, for example,_as described above by converting to
digital form and implementing the filtering as described
above. The two-dimensional spectrum of the resultant signal
is represented at 2210A, and it is seen that the original
horizontal and vertical frequencies, at half the high
definition sampling rate, are reduced to within the diagonal
band at the lower frequency standard definition
two-dimensional frequency cutoffs. The output of the filter
2210 is received by decimator 2215, which operates, in this
embodiment to decimate every other vertical line and retain
every fourth horizontal pixel. The pattern of decimation is
illustrated in another part of the diagram at 2260, and it
will be understood that this decimation can be achieved by the
decimator previously illustrated, with the line and field
inputs causing selection of the pixels to be retained in
accordance with the desired pattern. The resultant relative
image density is illustrated in the diagram at 2200. After
time base correction in the manner previously described, the
output of the decimator is coupled to one input of multiplexes
2120. The output of the multiplexes is coupled to a zero
padder 2260 and to a storage buffer for storing detail
coefficients. The output of zero padder 2260 reconstructs the
pattern shown at 2260A, using a padder of the type previously
illustrated. This signal is coupled to a standard definition
two-dimensional diagonal low-pass filter 2265, which operates
in the same manner as filter 2210, and produces a spectrum as
illustrated at 2265A, without aliasing. The output of filter
2265 is one input to a summing circuit 2270. The other
multiplexes output is coupled to detail coefficient storage
buffer 2280, whose output is coupled. to an inverse cosine
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23
transform circuit 2285, which: may.be_a.chip of the type
described in the above referenced Canadian Patent Application
Serial No. 2,079,318. The output of circuit 2285 is the other
input to summing,circuit 2270. The output of summing circuit
2270 is, in turn, the negative input to difference circuit
2207 whose output.is coupled to cosine transform circuit 2135,
and the output of this circuit is coupled to a detail
component selection circuit 2237. The circuits 2135 and 2137
may, again, be of the type described in the above referenced
Canadian Patent Application Serial No. 2,079,318. The output of
circuit 2237 is time base corrected (block 2240), and is then
the other input to multiplexes 2120. In operation, this
circuit uses (as an example), selected transform components in
the time slot made available by decimation. The decoder,
after demultiplexing, can utilize circuitry in the dashed
enclosure 2250 to recover the components of the signal and add
them to obtain an HDTV output. It will be understood that the
same principles could be applied for non- transformed detail
components.
It will also be understood that the two-dimensional
modulation of video into the high frequency diagonal portion
of the spectrum (for subsequent recovery) can be utilized to
reduce interference between signals, for example in a
co-channel situation. Fig. 23 illustrates transmitters A and
B in separate broadcasting regions, and a receiver which can
receive interfering signals from the transmitters. If one of
the transmitters is utilizing a two-dimensionally modulated
video signal (for subsequent conversion, as described above),
perceived interference will be substantially reduced.
It is known that pictures can alternatively be
represented in terms of their spectral content. The discrete
Fourier transform of an entire image having N spatial pixels
will contain N unique. frequency components and therefore
generally requires the same transmission bandwidth needed to
send spatial image information. In the embodiment to de
described next, spectrally transforming the augmentation
detail can provide advantages,: for example~because the lower
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24
spectral components usually sent in the conventional channel
need not be-duplicated, and the transformed augmentation
components can be dynamically selected in a manner which can
better satisfy the needs of the human visual system. Fig s 24
and 25 illustrate exemplary band divisions of the Fig. 6
spectrum into two and four bands, respectively. In Fig. 25,
the bands have approximately equal spectral order, and are
numbered in descending order of visual priority. A four band
augmentation technique is set forth~in the embodiment to be
described, but other band selections (both as to the number of
bands and the spectral shapes and apportionments thereof) can
be employed.
Referring to Fig. 26, there is shown a block diagram of
an encoder in accordance with a further embodiment of the
invention, and which can be used to practice an embodiment of
the method of the invention. The encoder may be utilized, for
example, in the type of system illustrated in Fig. 1. The
use of codes or synchronizing signals, or of other means for
identifying or synchronizing channels, may be in accordance
with the teachings of U.S. Patent No. 4,800,426, or other
abovereferenced patents or publications.
The high definition video signal is coupled to a
complementary 2-dimensional spatial filter 910. The filter,
described further in conjunction with Fig. 27, operates, inter
alia, to separate the received HDTV signal into a conventional
resolution video signal and a detail signal. The encoder
spatial filter 910 can be in the form of two one dimensional
low pass finite impulse response (FIR) filters - one operating
in the vertical spatial direction cascaded with one operating
in the horizontal spatial direction. The cascading operation
acts to convolve the vertical and horizontal spatial images.
The two dimensional spectral response is obtained by
multiplying the responses of the two filters thereby providing
a rectangular spectral window in the two dimensional frequency
domain. Reference can also be made to the abovereferenced
U.S. Patent No. 4,628,344. [Of course, if separate high and
low resolution cameras or. other sources of video component
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signals are employed,. the-filtering:_may-not be necessary or
may be of a different form.J : The conventional-resolution
video signal is coupled-to-a scan converter 920 which is
utilized to produce video having conventional scanline and
element format, for example 483 visible lines as in NTSC. The
scan-converted video, is coupled to encoder 930, for example an
NTSC encoder. The_encoded conventional resolution video
signal can be stored, transmitted, or otherwise processed in
known fashion. A motion-indicative signal can also be
included in the conventional video channel in order to obtain
enhanced operation at receivers having certain processing
capabilities.
In the present embodiment, the high definition detail
component is processed using predetermined regions (or
"tiles") of the picture. In this embodiment, the tiles are
square and there are 8x8 pixels per tile, although other tile
sizes and configurations could be utilized.
The detail augmentation channel includes transformation
of the detail signal using an orthogonal transform into the
frequency domain, such as by cosine transform, as represented
by the block 950. The particular transform bands to be
utilized (transmitted, in this case) are dynamically selected
as a function of motion for each tile, as represented by the
blocks 960 and 970, and described further in conjunction with
Fig. 28. In accordance with a feature of this embodiment, the
particular bands selected are determined, for those tiles at
which there is currently no substantial motion, as a function
of the motion history of such tile. In particular, the longer
the picture information at the tile remains substantially the
same, the more detail information is provided (transmitted, in
this case) for the tile, until all available detail has been
provided. In the present embodiment, the motion indicative
signals are generated by detecting motion of the transformed
tiles (e. g. Figs 28 and 30), although it will be understood
that motion could be detected using the detail component or
other suitable video representation. The selected band
components (if any) for each tile, and motion status signals
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are coupled, in.the present:embodiment, via multiplexes 980, -
to the transmitter and/or storage medium.
Fig. 27 illustrates a preferred arrangement for the
encoder scan conversion. The low (or conventional) resolution
output of the 2D spatial filter 910 (e.g. at 1125 lines) can
be coupled to a first down scan converter 2720 that converts
to conventional 525 line (NTSC) format, for coupling to the
conventional transmitter (e. g. 210 in Fig. 1). An up scan
converter 2730, that is identical to one that will be employed
in the receiver's decoder (e. g, block 3115 of Fig. 31 below),
can then be used to up-convert back to 1125 lines. The result
can be subtracted from the high resolution component, using
difference circuit 2750, to obtain the desired high-pass
detail components. A compensating delay 2710 can be employed,
as shown, and throughout the description hereof it will be
understood that any necessary compensating delays can be
employed, as known in the art.
Referring to Fig. 28, there is shown, in further detail,
a block diagram of the portion of the encoder that processes
the detail signal for coupling to the augmentation channel and
which was represented in Fig. 26 by the blocks 950, 960, 970
and 980. A demultiplexer 1105, line fifos 1110 and
multiplexes 1115 serve, in known fashion, to put the detail
signal in appropriate format to be received by the transform
chip 1120 which, in the present embodiment may be an INMOS IMS
A121 Discrete Cosine Transform chip. The transform chip 1120
receives a pixel clock, which is also received by a
coefficient counter 1125. The transform chip also receives a
"next tile" indication, which can be derived as the pixel
count modulo 64, and this indication is also coupled to the
coefficient counter 1125 and to a tile position counter 1130.
The tile position counter 1130 also receives a "next frame"
indication. The coefficient counter 1125 keeps track of
which of the transform coefficients (64 of them, for this
example) is being output from the transform chip 1120, and the .
tile position counter 1130 keeps track of the position (x, y)
of the tile being processed, the tiles typically being
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processed sequentially, a row at a time.--.-A-look-up table
1135, which may be a.read-only memory ("ROM"),translates the
coefficient identification information from counter 1125 to
part of an address at which coefficients from transform chip
1120 are to be stored in two band storage RAMS 1150 and 1155,
respectively. The band storage RAM 1150 is dual ported; that
is, it can be. accessed at either an input port, using and
input address or, independently, at an output port using an
output address (which, in this case, is obtained from a tile
control processor 1175). The band storage RAM 1150 is used to
store the band components; that is, the groups of transform
coefficients that comprise individual bands of the frequency
. spectrum, such as the four bands labeled 1, 2, 3 and 4 in Fig.
25. In the present example it is assumed that each of the
four bands, 1-4, has five coefficients, which that means that
twenty of the possible sixty-four coefficients are actually
utilized to represent the shaded spectrum shown in Fig. 6, the
other forty-four coefficients approximately representing the
remaining regions shown in Fig. 5, and not beingwecessary, as
first explained above. As will be explained, the appropriate
band component will be read out of the band storage RAM 1150
to a multiplexer 1165 which also receives indications of
motion flag storage status from the flag storage RAM 1170.
These signals are applied to a fifo 1185 and eventually to a
transmitter (or storage, as the case may be), such as
transmitter 275 of Fig. 1.
The other band storage RAM 1155 may be single ported, and
is used in this embodiment for the purpose of motion
detection. The RAM 1155 receives the same coefficient
information as the RAM 1150, but each time it receives a new
coefficient, it reads out the corresponding coefficient from
the previous frame (that is, the coefficient stored at the
address to be occupied by the corresponding coefficient of the
current frame), so that motion detection can be implemented by
the circuit,1160, which is.shown.:in further detail in Fig. 30:
Referring momentarily: to Fig. 30, the current band component
(from transform chip 1120 - Fig. 28), and-the corresponding
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previous frame;band_cornponent (from band storage-RAM 1155 -
Fig. 28) are.received.by_a_difference_circuit 1310 whose
output is coupled to an absolute value circuit 1320. An
accumulator 1330 accumulates the total of the absolute values
of the differences for each tile (the resetting and read-out
of the accumulator being enabled by a next tile indication),
and its output is compared against a predetermined threshold
level. If the threshold is exceeded, a motion indication
signal is output from comparator 1340. As seen in Fig. 28,
this signal is received by flag storage RAM 1170, which is
also a dual.ported RAM.-. In the present embodiment there are
five motion.flag statuses,,as follows: motion flag status 1
indicates motion, and that the first of the four bands should
be sent; motion flag status 2 indicates that there has been no
motion for one frame, and that band 2 should be sent; motion
flag status 3 indicates that there has been no motion for two
frames, and that band 3 should be sent; motion flag 4
indicates that there has been no motion at the tile for three
frames, and that band 4 should be sent; and motion flag status
0 indicates that there has been no motion at the tile for four
or more frames, and that no spectral information should be
sent (all four bands having already been sent). The tile
control processor 1175, which may be any suitable
microprocessor or part thereof, dedicated logic, or integrated
circuit, controls the flag storage RAM 1170, as will be
described. Fig. 29 is a flow diagram of a routine for
controlling the tile control processor 1175. The block 1205
represents the initializing of indices i and j which represent
the position of the tile in the two dimensional tile array. A
sync code is then sent (block 1210), as indicated in Fig. 28
by an output of tile control processor to a sync code
generator 1180 which outputs a sync signal to one input of an
analog multiplexes 1195. The motion flag status for tile
(i,j) is then sent to the fifo 1185 from the flag storage RAM
1170 via the multiplexes 1165, as represented by the block
1215. This is implemented by sending the'address (i,j) to the
output port of the flag storage R.AM 1170, and enabling the
a
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multiplexes 1165 to pass_the flag status information-to the
fifo 1185. Inquiry is then made (diamond 1220) as to whether w
the motion flag status is zero. If so, there has been no
motion at this tile for at least the last four frames, and all
of the band information has already been sent, so no spectral
information will be sent for this tile. In such case, the
diamond 1250 is entered directly. If the motion flag status
is not zero, band information will be sent from the band
storage RAM 1150 to,the fifo 1185, and this is implemented by
the loop 1243. An index k is initialized at zero, as
represented by the block 1225. The index k is used to
identify the five components of each band. Each time k is
incremented (block 1240) the band component at the address
[i,j,flag(i,j),kJ is loaded from the band storage RAM 1150
into the fifo 1185 via the multiplexes 1165, the multiplexes
being controlled to load information during this phase from
the band storage RAM 1150 by the line in Fig. 28 labeled
"select flag or band component". The address is seen to
include the tile position [(i,j)J, the motion flag status
[flag (i,j) - which determines the band to be used, in
accordance with the above-listed rules), and the component of
the band [kJ. When the loop 1243 is complete, the inquiry of
diamond 1235 will be in the affirmative, and block 1245 will
be entered, this block representing the updating of the motion
flag status in accordance with the above-listed rules. Stated
another way, the motion flag status at the address (i,j) is
accessed in the flag storage RAM 1170 and is incremented
modulo 5. Inquiry is then made (diamond 1250) as to whether
the last tile of the row has been reached. If not, i is
incremented (block 1260), block 1215 is re-entered, and the
loop 1263 is continued until the row is complete. Index i is
then initialized for the next row, and inquiry is then made
(diamond 1255) as to whether the last row of tiles has been
considered. If not, j is incremented (1270), block 1215 is
re-entered, and the loop 1273 is continued until all tiles
have been considered, whereupon the block 1205 is re-entered
for processing of the tiles of the next frame.
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The.information in_fifo 1185 is clocked out preferably at
a fixed. clock rate for a given_portion of the transmitter
frames, to digital-to-analog converter 1190, and-then-to
transmitter via analog multiplexes 1195. The multiplexes 1195
is controlled to pass the output of digital-to-analog
converter 1190, except when a sync code is being applied, as
previously described.
Referring to Fig. 31, there is shown a block diagram of
an embodiment of the decoder. In general, the decoder
receives a conventional channel (e.g. 525 line input) and
converts it to a relatively low resolution image at the same
number of lines as the HDTV to be ultimately displayed or
recorded. Information from the augmentation channel is
received over a separate path, and is processed and stored in
a spectral memory (block 1445 in Fig. 31). The output of the
spectral memory is processed by an inverse transform chip
(block 3160 in Fig. 31), for example an inverse cosine
transform for the present embodiment, to obtain image detail
which is added to the relatively low resolution scan-converted
image obtained from the conventional resolution channel.
This is implemented by the summer 3170 in the Fig. 31
embodiment. This signal is converted to analog form and can
then be coupled to a suitable HDTV display and/or recording
means.
It can be initially noted that the timing relationship
between the conventional channel and the augmentation channel
is non-critical, and can be treated independently. (This is
because small delays between the low resolution components and
the detail components will generally not be noticeable to the
viewer.]
In the Fig. 31 decoder embodiment, an augmentation input
processor 3140 and a spectral-to-detail converter control
processor are employed. These functions can be implemented,
for example, by sharing a single microprocessor or with
separate microprocessors, or by dedicated logic or integrated
circuit means. The routine for controlling the augmentation
input processor is described in conjunction with the flow
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31
diagram of Fig.:.32, and_the routine for implementing the
spectral-to-detail converter control processor is described in
conjunction with the flow diagrams of Figs 33 and 34. The
pixel stream.output;from the inverse transform chip 3160 is
coupled to a fifo circuit 3165 which is described further in
conjunction with Fig. 35.
Turning now to the.detailed operation of the Fig. 31
embodiment, the video from the conventional receiver portion
is coupled to an.analog-to-digital converter 3105 and then to
a scan converter 3115, the scan converter also receiving the
necessary synchronizing information which is extracted by sync
detector 3110 and is to be used by the scan converter 3115 and
the spectral-to-detail converter control processor 3155.
The augmentation signal from the augmentation channel
receiver portion is digitized using analog-to-digital
converter 3120, and the augmentation sync is extracted (block
3125) and coupled to the augmentation input processor 3140
which, if in the middle of an operation, will asynchronously
terminate the process in progress and-return to the start of
the frame sequence in order to re-synchronize. The digital
data output from analog-to-digital 3120 is coupled, via a
demultiplexer 3130, to the processor 3140 or to one input of a
multiplexes 3135, the other input of which is a logical "0".
As will be recalled, the data has a flag status indication
followed, where appropriate, by spectral components, and the
augmentation input processor 3140 operates to control the
demultiplexer 3130 to couple motion flag status indications to
the processor 3140 and spectral component data; via
multiplexes 3135, to the dual ported spectral data RAM 3145.
Reference can be made at this point to the flow diagram
of Fig. 32 which illustrates a routine for controlling the
augmentation input processor 3140. The diamond 1502, and the
associated loop, represent the waiting for detection of sync,
whereupon the tile position indices, i,j, are initialized
(block 1504). Inquiry is then made (diamond 1506) as to
whether the motion flag status is 0.- If so, no spectral data
will follow the motion status flag, the next portion of the
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routine is bypassed, and the diamond 1575 is entered directly:
If the flag status is not,_0,_inquiryis made (diamond 1508)
as to whether the flag status is 1. If not, the block 1560
is entered directly. If so, however, motion at the current
tile is indicated, and the high- resolution bands in spectral
data RAM 3145 therefore contain obsolete values. In such
case, the next portion of the routine is utilized to remove
these obsolete values from RAM 3145 and to insert a "0" via
multiplexes 3135. In particular, the band index is
initialized at 2 (block 1510), it being understood that it is
not necessary to remove existing data from band 1 of storage,
since the subsequent operation will cause insertion of new
spectral data into band 1 (the motion flag status being 1 for
this branch of the routine). The band component index k is
then initialized (block 1512), and the block 1514 is entered,
this block representing the setting of the component in
spectral data RAM 3145, at address [i,j,b,k), to 0. Inquiry
is then made (diamond 1517) as to whether the last k has been
reached. If not, k is incremented (block 1520), block 1514
is re-entered, and the loop 1519 continues until all band
components have been considered. Then, inquiry is made
(diamond 1525) as to whether the last band has been reached.
If not, the band index is incremented (block 1529), block
1512 is re-entered and the loop 1530 is continued until all
bands have been considered. The block 1560 is then entered,
and k is initialized. The received spectral component will
then be stored in the spectral data RAM at address
[i,j,flag(i,j),k], as represented by the block 1565. Inquiry
is then made (diamond 1567) as to whether the last k has been
reached. If not, k is incremented (block 1569), and the loop
1570 is continued until all components of the received
spectral band have been read into their appropriate addresses
in spectral data RAM 3145. The diamond 1575 is then entered
(and is also entered directly from the "yes" output branch of
diamond 1506), and inquiry is made as to whether last i [that
is, the last tile of the row) has been reached. If not, i is
incremented (block 1578), diamond 1506 is re-entered, and the
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loop 1580_is continued until ~he last~i is-reached. When this
occurs, i.is initialized.to begin a new row (block 1582), and
inquiry is made as to whether the last row has been reached
(diamond 1585). If not, j is incremented (block 1587),
diamond 1506 is re-entered, and the loop 1590 is continued
until all tiles have been processed, whereupon the diamond
1502 is re-entered.
Referring again to Fig. 31, the spectral-to-detail
converter control processor is synchronized to the output of
scan converter 3115. When an indication of a start of frame
is received by processor 3155, it begins the routine of
controlling inputting of spectral data information from RAM
3145 to inverse transform chip 3160 via the multiplexer 3150.
Referring, in this regard, to the flow diagram of Fig. 33,
the sync is awaited (diamond 3302 and associated loop), and
the tile indices are then initialized (block 3305). A
coefficient index, c, is then initialized (block 3308), to
consider all coefficients (for example, 64 coefficients for
an 8x8 pixel tile) to be coupled, for each tile, to the
inverse transform chip 3160. Inquiry is made (diamond 3310)
as to whether c is used (it being recalled that only some of
the coefficients are utilized). If not, a "0" is sent to the
inverse transform chip 3160 by sending a command to the
control line of multiplexer 3150. [Alternatively, if it is
viable to permanently disable the not-used coefficients of
inverse transform chip 3160, this operation would not be
necessary.) If the coefficient is used, the block 3320 is
entered, this block representing the sending to the inverse
transform chip of the component in the spectral data RAM at
address [i,j,c). Inquiry is then made (diamond 3330) as to
whether the last coefficient has been reached. If not, c is
incremented (block 3332), diamond 3310 is re-entered, and the
loop 3335 is continued until all coefficients have been read
into the inverse transform chip 3160. When this has been
done for the current tile, the inverse transform operation is
initialized (block 3340, and the "start" line in Fig. 31).
Inquiry is then made (diamond 3360) as to whether the last
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tile of the row has been reached. If not, i is incremented
(block 3345), block 3308 is re-entered, and the loop 3350 is
continued until the row is completed: The index i is then
initialized for the next row (block 3365), and inquiry is
made (diamond 3368) as to whether the last row has been
processed. If not, j is incremented (block 3380), block 3308
is re-entered, and the loop 3385 is continued until all rows
of tiles have been processed. The diamond 3302 is then
re-entered to again await the sync.
The routine illustrated by the flow diagram of Fig. 34
is used to control the loading of tiles of output pixel data
into, and then out of, the fifo circuit 3165 of Fig. 31, the
fifo circuit being shown in Fig. 35. In the present
embodiment there are eight fifos, 3521-3528, and they each
receive the inputs from the inverse transform chip 3160.
However, only one fifo is enabled to load at a time, under
control of demultiplexer 3510. The demultiplexer 3510
receives the inverse transform clock and a fifo select
control from processor 3155. In particular, referring to the
routine of Fig. 34, the diamond 1710, and the associated
loop, represents the waiting for sync of the output video to
be generated. The completion of the inverse transform
computation for the current tile is then awaited (diamond 1715
and the associated loop), and a pixel index is initialized
(block 1720). The demultiplexer 3510 is then controlled to
select the fifo for the current pixel count (block 1725).
Inquiry is then made (diamond 1730) as to whether the last
pixel has been reached. If not, the pixel index is
incremented (block 1735), the block 1725 is re-entered, and
the loop 1740 continues until all pixels for the current tile
have been read into the fifos. Inquiry is then made (diamond
1750) as to whether all tiles have been processed. If not,
the tile index is incremented (block 1755), diamond 1715 is
re-entered, and the loop 1751 continues until all tiles have
been processed, whereupon the diamond 1710 is re-entered.
The pixel information in the fifos is clocked out under
control of demultiplexer 3540 which receives the video out
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clock and the lire out enable, as seen in Fig. 35. The
demultiplexer is controlled by the output of line counter
3550 which receives the line out enable, and, in the present
embodiment, is a modulo 8 counter. The counter 3550 output
also controls the multiplexer 3530 to select which fifo
output is coupled to summer 3170 (Fig. 31), so that the
information is read out a line at a time, after the 8x8 pixel
data is read into the fifos 3521-3528.
It will-be understood that the techniques hereof are
applicable regardless of the original resolution, and could be
used to advantage for bandwidth compressing moving picture
video information at any original bandwidth. It will also be
understood that when a substantial portion of the scene is
still (not in motion) for a substantial number of frame
periods (e.g. more than five frame periods or 1/6 of a
second), very little picture information will be transmitted
[since, as noted above, most tiles will be status "0"J. In
such case, the additional bandwidth could be used to
periodically send update information. Also, statistical
multiplexing among a number of channels of the type described
could take particular advantage of the dynamic bandwidth
characteristics of each channel.
