Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
SYSTEM FOR TRANSMITTING AND RECEIVING VIDEO SIGNALS USING
INTERPOLATION OF ADAPTIVE FACTOR
BACKGROUND OF THE INVENTION
The present invention relates to a system for transmitting and
receiving video signals, and more particularly an apparatus for
selectively modulating and demodulating the video signals by
obtaining block and picture element adaptive factors of the video
signal blocks.
Conventionally, the adaptive modulation is employed to suppress
noise added to a video signal during transmission, wherein a
transmitted video signal of low Level is enhanced in the transmitter,
and then reduced in the receiver by the amount enhanced at the
transmitter. A typical system using such a conventional adaptive
modulation for transmitting and receiving a video signal is shown in
Fig. 1, and the signal converting characteristics are shown in Figs.
2A and 2F3.
Referring to Fig. 1, a system for transmitting and receiving a
video signal by employing the conventional adaptive modulation
comprises an encoder at the transmission side and a decoder at the
receiving side.
The encoder comprises a first adaptive modulator 110, first
delay circuit 120, first multiplier 130, first non-linear converter
140, second adaptive modulator 150, second delay circuit 160, second
multiplier 170, and second non-linear converter 180. The first
adaptive modulator divides a video signal of low frequency band
received via a low band input terminal 101 into given adaptive
intervals, and finds out the maximum value of the signal in the
respective intervals, so as to produce a first adaptive factor f1 and
first index signal ID1. The first delay circuit 120 delays the video
signal of low frequency band for the period during which the first
adaptive factor f1 is obtained. The first multiplier 130 multiplies
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the delayed video signal of low frequency band by the first adaptive
factor f1, The output of the first multiplier 130 is non-linearly
converted by the first non-linear converter 140. Likewise, the second
adaptive modulator 150 divides a video signal of high frequency band
received via a high band input terminal 102 into given adaptive
intervals, and finds out the maximum value of the signal in the
respective intervals, so as to produce a second adaptive factor f2
and second index signal ID2. The second delay circuit 160 delays the
video signal of high frequency band for the period during which the
second adaptive factor f2 is obtained. The second multiplier 170
multiplies the delayed video signal of high frequency band by the
second adaptive factor f2~ The output of the second multiplier 170
is non-linearly converted by the second non-linear converter 180.
Meanwhile, the decoder comprises a first reverse non-linear
converter 210, first adaptive factor generator 220, first divider
230, second reverse non-linear converter 240, second adaptive factor
generator 250, and second divider 260. The first reverse non-linear
converter 210 clips the portions of the received signal below a given
level and non-linearly converts the adaptive modulated video signal
of low frequency band, which is received via a low band receiving
input terminal 201, into a signal to have the reverse characteristics
compared to the received signal. The first adaptive factor generator
2 2 0 generates the f first adaptive f actor f 1 corresponding to the f first
index signal ID1 received via a first index receiving terminal 202.
The first divider 230 divides the video signal of low frequency band
of the first reverse non-linear converter 210 by the first adaptive
factor f1 so as to recover the original video signal. The second
reverse non-linear converter 240 non-linearly clips the portions of
the received signal below a given level, and converts the adaptive
modulated video signal of high frequency band received via a high
band receiving input terminal 203 into a signal to have the reverse
characteristics compared to the received signal. The second adaptive
factor generator 250 generates the second adaptive factor f2
corresponding to the second index signal ID2 received via a second
index receiving terminal 204. The second divider 260 divides the
video signal of high frequency band from the second reverse non-
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linear converter 240 by the second adaptive factor f2 so as to
recover the original video signal.
Figs. 2A and 2B show the conversion characteristics of the low
and high frequency band video signals of the first and second non-
linear converter 140 and 180, respectively.
In such conventional transmitting/receiving system for a video
signal, the encoder divides the video signal into small blocks of
1U sub-bands, and multiplies each of the blocks by respective adaptive
factor to transmit. Meanwhile, the decoder divides the picture
element of each of the received blocks by the adaptive factor. This
method is specifically disclosed in Korean Patent Serial No. 91-1023
granted to the applicant of the present invention.
However, using this system, as shown in Fig. 3B, results in the
block effect, which causes the boundary of a picture to show blocks
due to additive noises when recovering the original video signal,
because if the difference between the adaptive factors increases in
the boundary portions of the picture considering the video signal in
one dimension, there considerably differs the degree of suppressing
the additive noises.
SUMMARY OF THB IIdVEIdTIOI~T
It is an object of the present invention to provide a means for
decreasing the block effect, whereby a block adaptive factor is
obtained according to the maximum value of the video signal blocks
and is interpolated to produce a picture element adaptive factor so
as to selectively subject the video signal to the adaptive modulation
considering the peripheral blocks.
It is another object of the present invention to provide a means
for decreasing the block effect, whereby the received adaptive factor
is interpolated so as to provide a picture element adaptive factor,
thus selectively subjecting the received video signal to adaptive
demodulation.
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According to the present invention, transmitting/receiving
system for video signals compressed into frequency band blocks,
comprises:
(a) an adaptive modulation circuit for receiving the video
signals of the respective blocks to obtain a block adaptive factor
and an index signal corresponding to the block adaptive factor,
transmitting said index signal to a channel, interpolating the block
adaptive factor so as to obtain a picture element adaptive factor,
and selecting a final adaptive factor among the block and picture
element adaptive factors according to the video signals of the
peripheral blocks;
(b) a delay circuit for delaying the video signals during the
final adaptive factor being produced;
(c) a multiplier for multiplying the video signal of the delay
circuit by the final adaptive factor;
(d) a non-linear converter for non-linearly converting the video
signals of the multiplier, and for transmitting converted signal to
the channel;
(e) a reverse non-linear converter for clipping the portions of
the adaptive modulated video signals below a given level, and for
converting the adaptive modulated video signals non-linearly but
reversely with the non-linear converter;
(f) an adaptive demodulation circuit for converting the index
signal into the corresponding block adaptive factor, and
interpolating said block adaptive factor to produce the respective
picture element adaptive factor being equal to that of the adaptive
modulation circuit, so as to selectively provide the block or picture
element factor according to the video signals of the peripheral
blocks; and
(g) a divider for dividing the video signals of the reverse non-
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linear converter by the adaptive factor of the adaptive demodulation
circuit so as to recover the original block video signals.
BRIEF DESCRIPfiION OF fiHE AfifiACHED DRAWINGS
The invention itself, as well as other features and advantages
thereof, will best be understood by reference to the following
detailed description of a particular embodiment, read in connection
with the accompanying drawings, wherein:
Fig. 1 is a block diagram for illustrating a conventional system
for modulating and demodulating a video signal;
Fig. 2 shows graphs for illustrating the characteristics of the
non-linear conversion of a video signal by Fig. 1;
Fig. 3 illustrates the relationship between the video signal
blocks and the adaptive factor;
Fig. 4 is a block diagram for illustrating a system for
modulating and demodulating a video signal according to the present
invention;
Fig. 5 is a block diagram for more specifically illustrating the
adaptive modulation circuit of Fig. 4; and
Fig. 6 shows the table of the block adaptive factors.
DEfiAILED DESCRIPTION OF A PREFERRED EMBODTMENfi
Referring to Fig. 4, a first adaptive modulation circuit 410
receives video signals of low frequency compressed into band blocks
to obtain a first block adaptive factor and a first index signal ID1
corresponding to the first block adaptive factor, and thereafter to
transmit the first index signal ID1 to channel. Then the first
adaptive modulation circuit 410 interpolates the first block adaptive
factor so as to obtain a picture element adaptive factor, and selects
as a first adaptive factor f1 either the block adaptive or picture
element adaptive factors according to the video signals of the
peripheral blocks. A first delay circuit 420 is to delay the video
signals of low frequency band during the first adaptive factor f1
being produced. A first multiplier 430 is to multiply the video
signal of the first delay circuit 420 by the first adaptive factor
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fl. A first non-linear converter 440 non-linearly converts the video
signals from the multiplier 430 to transmit to the channel.
A second adaptive modulation circuit 450 receives video signals
of high frequency compressed into band blocks to obtain a second
block adaptive factor and a second index signal ID2 corresponding to
the second block adaptive factor, and thereafter to transmit the
second index signal ID2 to the channel. Then the second adaptive
modulation circuit 450 interpolates the second block adaptive factor
so as to obtain a picture element adaptive factor, and selects either
the block adaptive or picture element adaptive factors according to
the video signals of the peripheral blocks, to thereby produce a
second adaptive factor f2. A second delay circuit 460 is to delay the
video signals of high frequency band during the second adaptive
factor f2 being produced. A second multiplier 470 is to multiply the
video signal from the second delay circuit 460 by the second adaptive
factor f2. A second non-linear converter 480 non-linearly converts
the video signals of the second multiplier 470 to transmit to the
channel. All these component circuits constitute the encoder.
Meanwhile, the component circuits of the decoder are as follows:
A first reverse non-linear converter 510 is to clip the portions of
the transmitted video signals below a given level, and to convert the
adaptive modulated video signals of low frequency band non-linearly
in a reverse mode with respect to the first non-linear converter 440.
A first adaptive demodulation circuit 520 converts the first index
signal ID1 into the corresponding block adaptive factor, thereby
interpolating the block adaptive factor to produce the respective
picture element adaptive factor being equal to in the adaptive
interpolator 413 of the encoder (following described). Thereafter
either the block or picture element factor is selectively produced
as the first adaptive factor f1 according to the video signals of the
peripheral blocks. A first divider 530 divides the video signals of
the first reverse non-linear converter 510 by the first adaptive
factor f1 from the first adaptive demodulation circuit 520 so as to
recover the original block video signals.
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A second reverse non-linear converter 540 is to clip the
portions of the video signals below a given level, and to convert the
adaptive modulated video signals of high frequency band non-linearly
in reverse mode with respect to the second non-linear converter 480.
A second adaptive demodulation circuit 550 converts the second index
signal ID2 into the corresponding block adaptive factor, and
interpolates the block adaptive factor to produce the respective
picture element adaptive factor being equal to in the adaptive
interpolator 413 of the encoder, so as to selectively provide the
block adaptive or picture element factor as the second adaptive
factor f2, according to the video signals of the peripheral blocks.
A second divider 560 divides the video signals of the second reverse
non-linear converter 540 by the second adaptive factor f2 of the
second adaptive demodulation circuit 550 so as to recover the
original block video signals.
The respective first and second adaptive modulation circuit 410
and 450 is more specifically described with reference to Fig. 5. A
maximum value detector 411 detects the maximum value of the received
video signal block. A block adaptive factor calculator 412 produces
the block adaptive factor corresponding to the maximum value from the
maximum value detector 411 and the index signal corresponding to the
block adaptive factor. An interpolator 413 interpolates the block
adaptive factor so as to produce the respective picture element
adaptive factor. A subtractor 414 produces the difference signal
between the block adaptive and picture element adaptive factors. An
absolute value converter 415 converts the output of the subtractor
414 into its absolute value. A comparator 416 compares the output of
the absolute value converter 415 with a given reference signal so as
to provide a first selection signal for selecting the output of the
interpolator 413 or second selection signal for selecting the block
adaptive factor according to whether the output of the absolute value
converter is greater or less than the reference signal. A selection
circuit 417 selects either the picture element or block adaptive
factor according to whether the output of the comparator 416 is a
first or second select signal.
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The adaptive factor for a low frequency band video signal is
shown in the table of Fig. 6A. The address levels extend from 0 to
127, index from 0 to 7, and the values of the first adaptive factors
f1 corresponding to each number of the index are 1,2,3,4,8,16,32,64.
The logic of the table of Fig. 6A is stored into the block adaptive
factor calculator 412 of the first adaptive modulation circuit 410
shown in Fig. 4.
The adaptive factor of a high frequency band video signal is
shown in the table of Fig. GB. The address levels extend from 0 to
127 , index from 0 to 7 , and the values of the second adaptive factors
f2 corresponding to each number of the index are
1/4,1/2,1,2,4,6,10,31. The logic of the table of Fig. 6B is stored
into the block adaptive factor calculator 412 of the second adaptive
modulation circuit 450 shown in Fig. 4.
In operation, an adaptive factor of each block is obtained and
interpolated so as to produce a respective picture element adaptive
factor for each of the picture elements of the block. If the present
position of the block is assumed as (i, j) as shown in Fig. 3A, the
signal of the block position (i, j) and the adaptive factors of the
peripheral blocks (left, right, up and down side blocks) are employed
to obtain the adaptive factor of each of the picture elements. In
this case, the final adaptive factor becomes relatively greater or
less by the interpolation, according to whether the adaptive factor
of the present block is less or greater thah the adaptive factor of
the peripheral blocks. Hence, if the difference between the current
block adaptive factor and the peripheral block adaptive factor
becomes great, the picture element adaptive factor is selected as the
final adaptive factor. However, if the final adaptive factor appears
to have a value too greater or smaller than the original block
adaptive factor and therefore causes degradation of the picture
quality in the flat portions of the video signal in adaptive
demodulation, the original block adaptive factor is used as the final
adaptive factor.
Hereinafter, the adaptive modulation and demodulation are more
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specifically described.
The video signal is coded into sub-bands to provide the block
video signals of high and low band. The block video signal of lola
band is applied simultaneously to the first adaptive modulation
circuit 410 and first delay circuit 420. The first adaptive
modulation circuit 410 finds out the maximum value of the low band
video signal within a given adaptive block interval, and compares the
maximum value with the transmittable maximum allowable value in the
interval, so as to produce the block adaptive factor for subjecting
the low band video signal to the adaptive modulation. The block
factor should meet the following Equation.
Block Adaptive Factor= K
hmax
Where K is the transmittable maximum allowable value for the low
band video signal, and ~hmax~ the absolute maximum value of the
signal within the adaptive interval. Here, the quantization of the
video signal usually takes 8 bits, and therefore K is 128.
In the present embodiment, the block adaptive factors is
obtained using not the above equation but the look-up table of Fig.
6. In order to obtain the adaptive factor, the first adaptive
modulation circuit 410 is constructed as shown in Fig. 5. The maximum
value detector 411 detects the maximum value of the low band video
signal within the adaptive interval, and the maximum value is used
as an address of the block adaptive factor calculator 412 storing the
look-up table of the adaptive factors as shown in Fig. 6A.
Thereafter, the block adaptive factor calculator 412 outputs a 8 bit
block adaptive factor corresponding to the input address and a first
3 bit index signal ID1 corresponding to the block adaptive factor
from the look-up table as shown in Fig. 6A.
The block adaptive factor is applied simultaneously to one input
of the selection circuit 417 and the adaptive factor interpolator
413. The interpolator 413 interpolates the input block adaptive
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factor to provide the respective picture element adaptive factor. The
subtractor 414 produces the difference signal between the block
adaptive factor and the picture element adaptive factor, and
difference signal is converted by the absolute value converter 415
into the absolute value that is applied to the comparator 416, at
which the absolute value is compared with the reference signal TH.
The reference signal LH is for selecting the picture element adaptive
factor as the first adaptive factor f1 when the difference between
the present block adaptive factor and the peripheral block adaptive
factor is relatively greater or smaller. Thus, the comparator 416
generates the first selection signal for selecting 'the output of the
interpolator 413 or second selection signal for selecting the block
adaptive factor according to whether the output of the absolute value
converter 415 is greater or smaller than the reference signal TH,
respectively. The selection circuit 417 selects as the first adaptive
factor f1 the picture element adaptive factor or the block adaptive
factor according to whether the comparator 416 generates the first
or second selection signal, respectively.
While the first adaptive modulation circuit 410 produces the
first adaptive factor fl, the first delay circuit 420 delays the
input low band video signal. Accordingly the first multiplier 430
multiplies the delayed low band video signal by the first adaptive
factor fl with amplification. Then the first non-linear converter 440
non-linearly converts the adaptively amplified low band video signal
by using a non-linear function with the characteristics as shown in
Fig. 2A, so as to amplify the picture elements of low level which are
not previously amplified at the first adaptive converter 410.
Meanwhile, the high band video signal is applied simultaneously
to the second adaptive modulation circuit 450 and the second delay
circuit 460. Likewise the second adaptive modulation circuit 450
produces the second adaptive factor f2 to subject the high band video
signal to the adaptive modulation, and produces the second index
signal ID2 corresponding to the second adaptive factor f2. In this
case, the maximum allowable value Ii is 32, and the high band video
signal is processed with 6 bits considering the components of the
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high band video signal are generally within the range of 0 to 63 [if
there are given 32 off-sets, the range is -32 to 31]. The look-up
table of Fig. 6B is used to find out the second adaptive factor f2.
If the maximum value (hmax~ exceeds 6 bits within the adaptive
interval of the high band video signal component input as an address,
the adaptive factor is made to have 1/2 and 1/4 so as to suppress the
amplitude.
Thus, in the second adaptive modulation circuit 450, the maximum
value detector 411 detects the maximum value of the signal within the
adaptive interval. The maximum value is applied as an address to the
block adaptive factor calculator 412 to produce the block adaptive
factor of the high band video signal and the second index signal ID2
of 3 bits corresponding thereto, thus transmitting to the channel.
As stated above, the picture element adaptive factor is obtained from
the high band block adaptive factor, and thereafter according to the
states of adaptive factor of the peripheral block is selected the
block adaptive factor or the picture element adaptive factor as the
second adaptive factor f2.
Meanwhile, the second delay circuit 460 delays the input high
band video signal during the second adaptive factor f2 being produced
by the second adaptive modulation circuit 450. The second multiplier
470 multiplies the delayed high band video signal by the second
adaptive factor f2 with amplification. The second non-linear
converter 480 non-linearly converts the adaptively amplified high
band video signal in conformity with 6 bits transmission by using the
non-linear function of the characteristics as shown in Fig. 2B, thus
amplifying the picture elements of low level which are not previously
amplified in the second adaptive modulation circuit 450. The
amplified picture elements are transferred to the channel.
There may be various methods whereby the adaptive factor
interpolator 413 of the first and second adaptive modulation circuits
410 and 450 interpolates the block adaptive factor. If the block
video signal has the picture element size of 4 X 3 as shown in the
follovring Table 1, the picture element adaptive factors are obtained
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from the present block adaptive factor and the upper, lower, right
and left block adaptive factors with respect to the present block
adaptive factor with imposing weight according to the positional
relationship of each picture element.
TABLE 1
all a12 a13 a14
a21 a22 a23 a24
a31 a32 a33 a34
all = + 1/4F + 1/4F
1/2F
a1 2 + 3/8F + 1/8F
=
1/2F
a13 = + 3/8F + 1/8F
1/2F
a14 = + 1/4F + 1/4F
1/2F
a21 = 1/2F + 1/2F
a22 = a23 1/2F 1/8F + F + F
= + + F
a24 = 1/2F + 1/2F
a31 = 1/2F + 1/4F + 1/4F
a32 = 1/2F + 3/8F + 1/8F
a33 = 1/2F + 3/8F + 1/8F
a34 = 1/2F + 1/4F + 1/4F
The adaptive modulated high and low band video signals together
with the first and second index signals ID1 and ID2 are transmitted
to the receiver, and processed in reverse mode of the transmitter so
as to recover the original high and low band video signals.
The adaptive modulated low band video signal is applied via the
channel to the first reverse non-linear converter 510, and the first
index signal TD1 is applied to the first adaptive demodulation
circuit 520. The first reverse non-linear converter 510 clips the
portions of the low band video signal below a given level through
coring process whereby the clipped portions of the low band video
signal are taken as zero (0), and performs the non-linear reverse
conversion of the video signal by using the conversion function of
the characteristics reverse to that of the non-linear function as
shown in Fig. 2A so as to chiefly eliminate the additive noises
contained in the signal portion of low amplitude.
The block adaptive factor converter 521 of the first adaptive
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demodulation circuit 520 receives the first index signal ID1 to
produce the block adaptive factor. In this case, the block adaptive
factor converter 521 has the black adaptive factor table of the low
band video signal as shown in Fig. 6A, and produces the block
adaptive factor corresponding to the first index signal ID1. The
block adaptive factor is applied simultaneously to the selection
circuit 526 and the adaptive factor interpolator 522 to produce the
respective picture element adaptive factor. Thus, the first adaptive
demodulation circuit 520 selects as the first adaptive factor fl the
picture element adaptive factor or the block adaptive factor
according to whether the difference between the present block
adaptive factor and the peripheral block adaptive factor. The first
divider 530 divides the low band video signal of the first reverse
non-linear converter 510 by the first adaptive factor fl of the first
adaptive demodulation circuit 520 so as to recover the original low
band video signal.
The second reverse non--linear converter 540 clips the portions
of the high band video signal below a given level through coring
process whereby the portions of the low band video signal below a
given level are taken as zero (0), and performs the non-linear
reverse conversion of the video signal by using the conversion
function of the characteristics reverse to that of the non-linear
function as shown in Fig. 2B so as to chiefly eliminate the additive
noises contained in the signal portion of low amplitude.
The second adaptive demodulation circuit 550 receives the second
index signal ID2 to produce the corresponding second adaptive factor
f2 in the same way that the first adaptive demodulation circuit 520
produces the first adaptive factor fl. In this case, the second
adaptive factor f2 may be obtained by using 'the adaptive factor table
as shown in Fig. 6B.
The second divider 560 divides the high band video signal of the
second reverse non-linear converter 540 by the second adaptive factor
f2 of the second adaptive demodulation circuit 550 so as to recover
the original high band video signal.
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Thus, the transmitter analyzes the adaptive factors of the
present block and the peripheral blocks of the high and low band
video signals so as to select as the final adaptive factor the block
factor or the picture element factor, multiplies the original video
signal by the final adaptive factor, and subjects it to non-linear
conversion. On the other hand, the receiver divides the adaptive
modulated high and low band video signals by the block adaptive
factor or picture element factor reversely with the transmitter, thus
reducing the additive noises as well as eliminating the block effect.
Although the invention has been described with reference to the
specific embodiment, this description is not meant to be construed
in a limiting sense, as other embodiments of the invention will
become apparent to person skilled in the art upon reference to the
foregoing description of the invention. It is therefore contemplated
that the appended claims will cover any such modifications or
embodiments as fall within the true scope of the invention.
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