Note: Descriptions are shown in the official language in which they were submitted.
~ 092/2~61 2 ~ ~ ~ 3 8 5 PCT/~92/~87
!
Synchronizing and image positioning methods- for a
video display
Field of the Invention
The invention relates to a method of adjusting
the position and/or size of an image displayed on a
screen of a video display device, and to a method of
synchronizing a video display device with a video
signal.
8ackground of the Invention
In most modern personal computers (such as IBM
PC compatible) a VGA (Video Graphics Array) display
adapter has replaced the former EGA, CGA, MDA and HGC
adapters. All these display adapters typically
control a video display terminal with one or two
deflection frequencies. In addition, all of the dis-
play adapters support both character and graphics
display modes. Display adapters for higher-resolution
displays are almost exclusively graphics based, sup-
porting primarily MS-Windows, OS/2 Presentation
Manager or X-Windows user interfaces or CAD software.
It is characteristic of all these systems that
the display device is controlled by means of syn-
chronizing signals. Vertical deflection signals align
the image vertically on the screen of the display
device so as to utilize the entire screen as
efficiently as possible. Correspondingly, a hori-
zontal deflection signal aligns the image in the
horizontal direction. The timings of the deflection
signals depend on the employed display device and
display adapter. For example, a cathode-ray tube
3~ (CRT) display device requires a predetermined time ~o
~W092/2~6l ~ 8`3 PCT/~92/
retrace the electron beam to the start of the
scanning of the next line or field. The retrace time
is controlled by horizontal and vertical blanking
signals which indicate the position of the active
image area on the screen. The resolution of the dis-
play device is determined by the applied technology
and the technical solution, being typically e.g.
640x480, 800x600, 1024x768 and 1280x1024. The
blanking period or passive display period (e.g. the
retrace time of the beam) can be subdivided into a
front porch and a back porch and a synchronizing
pulse.
Display devices typically have horizontal de-
flection frequencies and display refreshing fre-
quencies which are determined by the frequencies ofthe horizontal and vertical synchronizing signals. To
achieve an advantageous technical structure for the
display device, a usual inexpensive solution is to
use a display device with one deflection frequency.
This means that the display device is capable of syn-
chronization with video signals only within a
relatively narrow frequency band of the horizontal
deflection signal. The display device is not usually
very sensitive to the vertical deflection, but it is
synchronized fairly well with very different vertical
deflection frequencies. Especially in CAD
applications, which require very high resolution,
both the vertical and horizontal deflection signals
of the display adapter have to be very accurately
defined, and they must not deviate from the values
specified for the display device. In this way, a very
high image quality is achieved at the expense of low
price and versatility.
The most recent display devices are usually so-
called multi-frequency displav devices, and so they
WO92/20061 ~ } ~ `31~ PCI`/~192/00087
~.'.
~.
are able to synchronize and operate within a very
wide range of horizontal deflection frequencies as
well within a wide range of vertical deflection
frequencies. These display devices offer various
adjusting possibilities for the user. When the dis-
play device is synchronized with the video signals of
the display adapter, the image is usually positioned
aside, and so the user has to align the image by
using the above-mentioned adjustments. The display
devices may comprise preselected and preset timing
modes, which the display identifies automatically and
adjusts the position of the image in accordance with
the manufacturer's adjustments.
The position of the image on the screen is
usually determined by programming the position of a
synchronizing pulse (HSYNC or VSYNC) in relation to
the active dlsplay period. The position of the image
can also be changed by varying the length of the
synchronizing pulses. The size of the image can be
adjusted by software by varying the duration of the
passive display period or by changing the polarity of
the synchronizing pulses (polarity adjustment is used
e.g. in a VGA environment). This technique is used
mainly to adjust the size of the image in the
vertical direction, whereas it is hardly ever used
for image adjustment in the horizontal direction,
because the horizontal deflection frequency would
also be affected, and this would also greatly affect
the vertical deflection frequency, which should be
kept as high as possible and which one is not ready
to sacrifice. In addition, the most common display
device applications are based on one horizontal de-
flection frequency, and therefore it is desirable to
maintain compatibility to these applications, too. A
change in the horizontal deflection frequency also
W0 92/2~K~ 5 PCT/~92/~ ~
easily affects the position of the image.
The vertical deflection control is formed of
the horizontal deflection signal, and it is usually
very easy to program as multiples of the horizontal
deflection pulses (correspondingly also the active
display period and the front (VFP) and back (VBP)
porch). The horizontal deflection signal, instead, is
formed of the multiples of a character clock, and
these are considerably more difficult to change by
software on account of the technical restrictions
imposed by the used technical applications. A charac-
ter clock signal is formed of the multiples of the
video dot frequency, and both of these are dependent
on the hardware of the equipment and it has not been
possible to program them. In graphics based applica-
tions, one character clock period commonly comprises
8 or 16, in text modes also 7, 9 and 18, video dot
clock periods. The position or size of the image can
thus be adjusted by software only by steps of at
least eight pixels, and so the adjustment appears as
rough jumps on the screen, and a smooth and accurate
adjustment cannot be achieved.
Computer application programs are drafted to
comply with specific resolutions used as standards,
which determines the available active image area on
the screen very accurately. The programmatically
selectable parameters affecting the adjustment of the
image are also generally preselected and bound to the
technical application. For example, video dot fre-
quencies are often generated by the oscillator orcrystal circuits of the display adapter, which gener-
ate only one video frequency per one circuit, and so
the display adapter supports only few display
standards and resolutions. The most recent circuits
based on frequency syn~hesis (phase-locked loops) are
W092/20~l 2 ~ PCT/~92/~87
.
able to generate several frequencies, and so one and
the same display adapter is able to support several
different resolutions and different horizontal and
vertical deflection frequencies for different display
devices. When the display mode is to be changed, the
display adapter selects the video frequency proper
for the new display mode and the other parameters
required by the selected display mode. The final ad-
justment of the position and size of the image on the
screen is then performed by utilizing the adjustments
of the display device.
Disclosure of the Invention
An object of the invention is to provide a more
versatile and more accurate adjustment of the posi-
tion and size of an image on the screen of a display
device than what has been possible previously.
Another object of the invention is to simplify
the synchronization of a video display device with a
video signal.
The first object is achieved by means of a
method according to the invention for adjusting the
position and/or size of an image displayed on a video
display device, which method comprises the steps of
claim 1.
The basic idea of the invention is that,
instead of adjusting the position and size of the
image on the screen by utilizing the adjustments of
the display device itself, the properties of the
video signal itself are adjusted by the software of
the microcomputer by varying the video dot frequency
of the video source, such as a display adapter, while
simultaneously varying the conventional programmable
video control parameters in accordance with various
algorithms in such a way that the best possible image
WO92t2~Kl ~ PCT/~92/~ ~
is obtained with the display device used in each par-
ticular case. Increase or decrease in the video dot
frequency, while. the line frequency is maintained
substantially constant, causes a corresponding
decrease or increase in the width of an individual
image element, i.e. pixel, on the screen and thus in
the size of the entire image. As all video signal
timing components are multiples of the video dot
clock cycle, it is essential that when the video dot
clock cycle is changed, at least the parameters
determining the number of the video dot clock cycles
in the horizontal deflection period should be changed
s$multaneously so that the horizontal deflection fre-
quency is maintained substantially unchanged. As the
video dot frequency can be changed by very small
steps, the accuracy which can be achieved in the
adjustment of the position and size of the image is
only a fraction of the size of an individual pixel,
- while previously the accuracy has been several
pixels. The adjustment of the position and size of
the image can be performed "smoothly" and accurately
as desired by the user without any compromises. The
video dot frequency can be selected by software from
a great number of predetermined frequencies or by
means of a fully programmable synthesis video dot
frequency generator. Accordingly, the only essential
modification required e.g. in the present-day display
adapters is a video dot frequency generator of a new
type or, at best, only a new mode of operation of the
previous generator is required, so the invention can
be realized very advantageously.
The present invention, however, also offers new
possibilities to realize the display device at a low-
er cost, because the adjustments of the position and
size of the image can be omitted from the display
092/2~Kl ~ PCT/~92/~87
device and performed by software, and the user can
control the adjustment e.g. from the keyboard of the
computer or by means of a mouse. Moreover, the inven-
tion provides the best possible quality of the image
even with less expensive (lower quality) display
devices, as deviations can be corrected easily and
accurately. Similarly, displacements in the position
and size of the image due to ageing of the components
can be compensated for by the user easily and
accurately, which increases the service life of the
display device and facilitates maintenance.
Furthermore, many other properties are achieved, such
as dynamic stepless zooming.
Further, as the video dot frequency can be
altered by sufficiently small steps, a video fre-
quency with which the horizontal deflection of the
display device under examination is synchronized can
be found by varying the video frequency. Thereafter
the vertical deflection can be synchronized and the
adjustments of the position and size of the image can
be carried out in accordance with the invention. The
invention provides compatibility with nearly all dis-
play devices irrespective of their horizontal and
vertical deflection frequencies and resolutions. On
the other hand, the display devices may be less
expensive single-frequency displays and still have
better display properties than the conventional
multi-frequency displays.
The invention is also concerned with a method
of synchronizing a video display device with a video
signal when at least the vertical and horizontal de-
flection frequencies and resolution are known amongst
the electrical properties of the video display
device. The method is characterized in that display
adapter control parameters are calculated from said
WO92/2~K1 PCT/~92/~87
~ 3
known properties of the video display device, the
control parameters being utilized to adjust the video
dot frequency of a video signal to be applied to the
video display device and the numbers of the video
clock cycles contained in the horizontal deflection
period, the blanking period, the display period, the
front porch period and/or the back porch period to
such values that the display device is synchronized.
As the small-step ad~ustment of the video fre-
quency enables a suitable video signal to begenerated for any display device, the required video
dot frequency and other parameters can be calculated
easily when the deflection frequencies and resolution
of the display device are known. In this way, the
user is able to make a desired display device
synchronize with a video signal by inputting the
electrical specifications of his display device to
the calculation program. Alternatively, the elec-
trical specifications may be obtained e.g. from a
program disk supplied with the display device. De-
fault values for the position and size of the image
can be obtained from the same disk e.g. by giving the
length of the front and back porch and the display
period and the position of the synchronizing pulses,
so that the display is immediately ready for oper-
ation. In this way, the invention makes it con-
siderably easier to set up a new display device. As
the specifications of the display devices can be
given as frequency and time units and resolutions,
the memory space occupied by them is only a fraction
of that reguired for storing the parameter tables
used previously for display adapters.
W092/2~61 2 ~ O ~ 3 ~ ~ PCT/~92/~87
` !
Brief Description of the Drawings
In the following the invention will be
described in greater detail by means of embodiments
with reference to the attached drawings, in which
Figure 1 is a block diagram of a computer
display system in which the method according to the
invention can be applied;
Figures 2 and 3 show a timing diagram illus-
trating the horizontal and vertical synchronizing
signals of a video signal; and
Figures 4 and 5 illustrate the screen of a
video display device and how the image is positioned
on the screen by the synchronizing signals.
Preferred Embodiments of the Invention
The invention may be employed for adjusting any
display device controlled by a video signal. Such a
video display may be a cathode-ray tube display,
liq~id crystal display, plasma display, electro-
luminance display, etc. Even though the primary range
of applications of the invention is within the com-
puter display systems, the invention can also be
applied to image adjustment in digital television
sets, for instance.
Figure 1 shows a computer system with a display
system in which the invention can be applied. The
computer system comprises a central unit (CPU) 7, to
which a keyboard 3, a mouse 8 and a display system
with a display device 2 can be connected. The display
system comprises a video display adapter l, which is
connected through a bus interface 6 to the central
unit ( CPU ) or the like 7 of the computer. The display
adapter or graphics controller 1 incorporates a
raster display memory 5 having a storage location for
each pixel o~ a displayed image. The display adapter
W092t2~Kl ~ PCT/~92/~
generates a video signal VIDEO (which may comprise
several different physical signals), which is applied
through a video interface 9 to control the display
device 2.
The display adapter 1 further comprises an
adjustable video frequency generator 4 the output
frequency fDcLK of which is controlled by a frequency
control signal FCONTR. The generator 4 may be e.g.
the frequency synthesizer circuit SC11410 or SC11411
of Sierra Semiconductor Corporation, or the frequency
synthesizer circuit ICS1594 of Integrated Circuit
Systems Inc. In practice, in all the above-mentioned
circuits, the control signal FCONTR of Figure 1 is a
serial interface through which the display adapter 1
can write control data into the control registers of
the synthesizer circuit 4, By means of the control
data of the registers practically any frequency can
be selected as the output frequency FDCLK~
Figure 2 is a timing diagram, which illustrates
deflection or synchronizing signals controlling the
horizontal deflection or scanning of the video
signal. A horizontal line or horizontal deflection
period HP~R means a period during which one hori-
zontal line is scanned from the left to the right
across the screen and back to the start of the next
horizontal line. The HPER comprises an active display
period HACTIvE~ which determines the active image
area on the screen and during which the image data
read from the raster memory 5 is displayed; and a
blanking period HBLANK, which comprises at least a
front porch HFP, a synchronizing pulse HSYNC and a
back porch HBP. For example, the returning or retrace
of the electron beam of the cathode-ray tube to the
start of the next line takes place during the blank-
ing period HBLANK. All the above-mentioned periods
092/2~K1 21 a ~ 3 ~ ~ PCT/~92/~87
11
consist of the multiples of a character clock period
CCLK, the number of which is determined in each
specific case by control parameters Mi (integers) in
the following way:
HSYNC = M2 * CCLK
HFP = M3 * CCLK
HBP = M4 * CCLK
HACTIVE = M5 * CCLK
HBLANK = HFP + HSYNC +HBP
HPER = HBLANK + HACTIVE = M6 CCLK
M6 = M2 + M3 + M4 +M5
The character clock cycle, in turn, comprises
the multiples of a video dot clock cycle DCLK =
l/fDCLK, whereby CCLK = Ml * DCLK. The character
clock CCLK may also be equal to the video clock DCLK.
In most cases, Ml = 8 so that one character on the
display contains eight pixels in the horizontal
direction. With the most common resolutions, the
values of the control parameters will thereby be:
640x480 (M5 = 80)
800x600 (M5 = 100)
1024x768 (M5 = 128)
1280x1024 (M5 = 160)
The image adjustment parameters may also be
selected in some other way. One special case is over-
scanning which adds a coloured peripheral area around
the active image area. This area can be incorporated
in the HFP/HBP area or the HACTIvE area, depending on
the case.
Figure 3 shows a corresponding timing diagram
for the control or synchronizing signals of the
vertical deflection. A field or vertical deflection
period VPER comprises a display period VACTIvE and a
blanking period VBLANK which contains at least a
front porch Vr P, a vertical synchronizing pulse VSYNC
W092/2~Kl ~ ~0 ~ 12 PCT/~92/~ ~
and a back porch VBP. All the above-mentioned control t
periods of the vertical deflection are formed of the
multiples of the horizontal deflection period HPER,
the number of the multiples being determined in each
5 particular case by programmable control parameters Ni
(integers).
Figure 3 illustrates how the video image is
positioned on the screen of the video display device
2 by the above-mentioned control signals. The
lO durations of the active display periods HACTlvE and
VACTIvE in relation to those of the periods HPER and
VPER determine the width and height, that is, the
size of the displayed image. The positions of the
synchronizing pulses HSYNC and VSYNC in relation to
l5 the respective active display periods HACTIvE and
VACTIvE determine the position of the image in the
horizontal and vertical direction. Conventionally,
only a coarse adjustment of the position and size of
the image has been possible by varying the control
20 parameters Mi with the accuracy of the character
clock CCLK (eight pixels).
According to the invention the above-described
control signals of the horizontal and vertical
deflection and thus the position and size of the
image on the screen can be affected more accurately
and more smoothly by adjusting the video dot fre-
quency fDcLK generated by the generator 4 shown in
Figure l. This can be effected by software by alter-
ing the control data in the control registers of the
generator 4. In order that a desired accuracy and
smoothness would be achieved by the image adjustment
of the invention, the video dot frequency of the
generator has to be variable by sufficiently small
steps. In principle, an improvement over the prior
art is already achieved when the adjustment
092/2~61 ~ 3 ~ ~ PCT/~92/~87
13
resolution of the video frequency fDcLK is
DCLK < l/(Ml * DCLK) = fDcLK/Ml, that is, the
adjusting accuracy produced on the screen is greater
than the adjusting accuracy of Ml pixels. However,
the adjustment begins to be really agreeable and
accurate only when fDcLK can be selected freely and
the accuracy of the adjustment on the screen is one
pixel or higher. When the adjusting accuracy is a
fraction of a pixel, an individual pixel displayed on
the screen can be extended or narrowed very accurate-
ly by means of the invention.
The length of the cycle of the video dot clock
DCLK changes with the video dot frequency fDcLK. A
change in the cycle of the video dot clock DCLX auto-
matically changes the duration of the character clockCCLK and thereby the duration of the horizontal de-
flection period HPER, which may result in that the
synchronization is lost. Therefore, according to the
invention, the hori~ontal deflection frequency is
maintained substantially constant within the fre-
quency tolerance allowed by the display device; if
required, the value of the control parameter M6 and
thus the number of the DCLK clock cycles in the
horizontal deflection period HPER may be altered by
software in such a direction that the duration of
HPER remains substantially constant. In the preferred
embodiment of the invention, the value of the
parameter M6 is changed to the nearest smaller value
(M6 = M6 - 1) if the frequenCY fDCLK is to
creased and the dimensions of the image on the screen
increase, and correspondingly to the nearest greater
value (M6 = M6 1 lj (the dimensions of the image on
the screen decrease as the video dot frequency in-
creases), when the following condition is fulfilled
35 1 ~H - T I > TCCLK / 2, where T-~ is the desired
W092/2~K~ 3~5 PCT/~92/~
14
duration of the period HPER of the display device 2,
T is the programmed duration of the period HPER of
the display adapter 1 and TCcLK is the character
clock cycle.
Adjustment of the position and size of the image
According to the invention, the size of the
image on the screen is adjusted by varying the video
q cy fDcLK~ while maintaining the horizontal
deflection frequency substantially constant by means
of the parameters Mi. Figures 4 and 5 illustrate the
adjustment of the size of the image by the video fre-
guency. Assume that, in Figure 4, a video dot fre-
quency is increased while maintaining HPER and HSYNC
substantially constant by means of the parameters Mi
is fDcLKl. The DCLK clock cycle thereby decreases
with increasing video dot frequency, as a result of
which the duration of the display period HACTIvE also
decreases (the duration of HBLANK increases) and an
individual pixel narrows, thus causing the image area
on the screen to be narrowed in the horizontal
direction, as shown in Figure 5. Correspondingly, the
image area on the screen can be widened by decreasing
the video dot frequency. In the vertical direction
the adjustment of the image is carried out separate-
ly, which will be described later on.
According to the invention, the position of the
image on the screen is adjusted by programming the
position of the horizontal synchronizing pulse HSYNC
in relation to the display period HACTIvE by the
parameters Mi. The position of the image can also be
adjusted accurately (smoothly) by software by varying
the video dot frequency while aiming at keeping the
position of the pulse HSYNC constant in relation to
either edge of the active display period ~ACTIV~ by
~..W092/2~K1 2 ~ ~ ~ 3 ~ ~ PCT/~92/~87
means of the parameters Mi. Thus a change in the
video dot frequency causes a change in the size of
the active displaY period HACTIvE~ as a
which the "unfixed" edge of the image area is "dis-
placed" on the screen in the horizontal direction
with respect to the synchronizing pulse. The number
of the clock cycles DCLK contained in the front porch
HFP or the back porch HBP can be altered by means of
the parameters Mi in such a direction that the com-
bined duration of the display period HACTIvE and thefront or back porch period remains substantially
constant with varying video dot frequency.
As the horizontal deflection period HPER is
maintained substantially constant in the invention, a
change in the video dot frequency does not, in prin-
ciple, affect the vertical deflection. If the
vertical deflection is not adjusted, an increase in
the video dot freq~ency, for example, causes the
image on the screen to be flattened at the sides, as
shown in Figure 5, and the ratio between the width
and height of an individual pixel is not correct.
This dot aspect ratio is typically 1:1. Therefore, in
the invention, the number of horizontal lines blanked
during one VPER period, i.e. the height of the image,
is also altered by means of the parameters Ni when
the video dot freguency is changed in such a
direction that the ratio between the width and height
of the pixels remains substantially constant. The
height of the image on the screen may also be adjust-
ed e.g. by varying the polarity or length of thepulse VSYNC.
The computer system comprises a control soft-
ware effecting the adjustments according to the in-
vention. On the basis of instructions given by the
user and by utilizing predetermined algorithms, the
PCT/~92/~
16
control software determines control data determining
the required video dot frequency for the generator 4
and the respective Mi and Ni parameters for the
display adapter. T~e user controls the adjustment
e.g. by the keyboard 3, the mouse driver 8 or some
other peripheral device.
Storage of the positional and synchronizing data of
the image
When using the method of adjustment according
to the invention, it is possible to determine the
position and size of the image on the screen so that
it matches with the display device used by utilizing
the physical (electrical) properties of the display
device instead of the integer parameters of the dis-
play adapter circuit. It thereby suffices that the
following lnitial data are known for each resolution
to be used: the horizontal deflection frequency, the
vertical deflection frequency, the position of the
image in the horizontal direction (HSYNC, HFP, HBP)
and the position of the image in the vertical
direction (VSYNC, VFP, VBP). The final integer
parameters Ni and Mi required by the display adapter
1 and the control data of the generator 4 can be
calculated mathematically for each mode of the dis-
play device and the display adapter whenever the mode
is changed. This method of storing image adjustment
information e.g. enables more user-friendly proper-
ties to be achieved more easily and requires less
memory capacity for storing the control information.
In addition, the same initial data are directly
applicable to all display adapters irrespective of
their structure, as it is the calculation software
that determines the control parameters for each
particular display adapter. The image of a new
~092/2~61 ~ ~ PCT/~92/~87
2 1 ~
17
display device can be adjusted to the manufacturer's
set values simply by inputting the specifications of
the display device into the calculation software. The
specifications may be loaded into the calculation
software e.g. from a program disk supplied with the
display device.
Automatic search for the deflection frequencies of
the display device
If the above-mentioned electrical properties of
the display device are not known, the search for the
deflection frequencies can be effected by selecting a
suitable resolution and by maintaining HACTIvE and
HPER constant and by varying the video dot frequency
from a starting frequency to a first frequency at
which the synchronization of the horizontal de-
flection of the display device is observed. When the
display device is synchronized, the user can signal
the program about the synchronization by means of the
keyboard (or this may be performed by the display
device when it detects the synchronization). There-
after the video dot frequency is further increased to
a second frequency at which the synchronization of
the horizontal deflection is again lost. The user or
the display device gives another signal indicating
the loss of the synchronization. From these two
signals, the program can determine the synchronizing
range and the synchronizing center of the horizontal
deflection, such as the mean value of the first and
second frequencies, which is selected as a video dot
frequency. After the synchronization of the hori-
zontal deflection, the vertical deflection is syn-
chronized by maintaining the horizontal deflection
frequency and the video frequency substantially
cons~ant and by varying the length of the vertical
WO92/2~61 ~ 3 PCT/FI92/~
18
deflection period of a video signal applied to the
display device by means of the parameters Ni until it
is observed that the vertical deflection is synchron-
ized. Thereafter the synchronizing range and center
of the vertical deflection can be searched similarly
as above and then adjust the size and position of the
image on the screen as described above.
Dvnamic zooming of the image
The invention also enables the achievement of a
dynamic zooming effect of the image on the screen.
Referring to Figure 6, a partial image area 62 is
selected from a normal-size image area 61 to be dis-
played with normal resolution on the screen, the
partial image area being smaller than the normal
image area 61 and corresponding to an mxn memory area
having an origin (M1, N1) in an MxN-size raster
memory 5. The zoom effect of the partial image area
62 is achieved by allowing the video dot frequency to
decrease. The origin of the active image area to be
zoomed can be moved by programming the (M2, N2) co-
ordinate as the initial address of the image area
along a line (Mo~ No) -> (M1, Nl) when the zooming is
in progress. The resolution of the image area 62 de-
creases correspondingly with decreasing video dotfrequency. The physical size of the entire image area
(area 61) on the screen during the zooming of the
image area 62 remains sufficiently accurately un-
changed when the control parameter M5 of the display
period HACTIvE as well as the parameter M6 of the
horizontal period HPER and the position of the pulse
HSYNC pulse are altered in accordance with a suitable
algorithm depending on the requirements in each
particular case.
The invention has been described above with
2 1 ~
~092/2~61 PCT/~92/~87
19
reference to certain synchronizing and timing signals
HS, HBLANK, VS, VBLANK of the horizontal and vertical
deflection and their periods, such as HFP, HSYNC,
HBP HAcTIvE, VFP, VSYNC, VBP, VACTIVE which ca
found in one form or another in every video signal.
The format of the video signal and, in practice, the
number of discrete signal components to be trans-
ferred may, however, vary to a very great extent. For
instance, the horizontal and vertical deflection
signals can be transferred separately or in combina-
tion, the video signal may a composite video signal
(television), or an RGB video signal, an analogous or
. TTL level signal, etc. The invention is intended for
use in connection with all such various video signal
formats.
The drawings and the description related to
them are only intended to illustrate the present
invention. In its details, the invention can be
modified within the scope of the attached claims.
