Display apparatus having means for generating a test signal on the display to facilitate adjustment of a property of the displayed image

The display apparatus includes circuitry for generating video signals for the display of still or motion pictures on a CRT or other display device. The apparatus further includes an arrangement for generating a test signal to display a test image to facilitate adjustment of the brightness (black level) setting of the CRT. The test image includes adjoining regions (100,102) of black and below-black levels, to forming a first image feature which is invisible at the correct brightness setting. If the brightness setting is too high, the first image feature is visible and forms a symbolic instruction indicating the necessary corrective adjustment. The test signal may be stored with picture information on a storage device.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a video signal processing apparatus comprising 
means for generating video signals to enable the display of still or 
motion pictures on a connected display device, and means for generating a 
test signal to enable the display of a test image to facilitate user 
adjustment of a property of the display device to a correct setting which 
provides optimum representation of the pictures. 
Such apparatuses include television receivers, where the display device is 
included in the apparatus, but also VCR's and other video and interactive 
video reproduction apparatuses, including CDV, CD-I, Laservision, Photo-CD 
and computer workstations, where the display device usually comprises a 
separate monitor or TV receiver. 
The invention further relates to a method of storing pictures on a record 
carrier for subsequent reproduction via a display device having at least 
one user-adjustable display property, the method comprising: 
(a) storing picture information on the record carrier in a form suitable 
for reproduction by the display device; 
(b) defining a test signal suitable for causing the display of a test image 
including a first image feature imperceptible at a display property 
setting which is correct for the display of the stored pictures but 
visible when the display property deviates in a given direction from the 
correct setting; and 
(c) storing information defining the test signal on the record carrier 
together with the picture information, characterized in that the first 
image feature, when visible, forms at least part of a symbolic instruction 
to the user indicating the nature of the deviation and/or the necessary 
corrective adjustment. 
The accurate representation of pictures by the display device used with 
such apparatuses requires proper setting of the black level (brightness) 
and other properties of the display device (color, contrast etc.). This is 
particularly important when display devices such as cathode ray tubes 
(CRTs) and liquid crystal displays (LCDs) are used to represent natural 
photographic images, since CRTs and LCDs have very low dynamic range 
(contrast ratio) compared with photographic film. This makes it important 
to utilize fully the dynamic range that is available, by correct 
brightness setting. 
2. DESCRIPTION OF THE RELATED ART 
It is known that test images are useful tools in the setting of black 
levels, and DE-A-2 716 212 (PHD 77024) proposes a television receiver with 
a built-in test pattern generator. This test pattern, in common with many 
broadcast `testcard` patterns, includes adjoining regions of black and 
dark grey. If the brightness is set too low, the black and grey are 
indistinguishable, whereas, if the setting is correct, they are just 
visible as distinct features. The adjustment is necessary to maintain 
optimum dynamic range as viewing conditions (especially ambient lighting) 
change. 
A first problem with the known test images is that the person making the 
adjustment requires to know the significance of the pattern, and the 
correct procedure for its utilization. In practice, only an engineer, if 
anybody, uses the known test patterns. This may be satisfactory, for 
example, in a professional studio environment, where engineers are 
available and where the ambient lighting conditions are constant and 
carefully controlled. However, the problem addressed here and in DE-A-2 
716 212 is that, in the domestic and general business environment, 
engineers are not available, while the viewing conditions can vary widely 
and frequently. 
Another problem with the test pattern proposed in DE-A-2 716 212, and with 
the known broadcast test patterns, is that the unskilled user, even with 
reference to an instruction manual, is required to judge when the 
difference between the black and grey regions is "just perceptible". There 
is no visual confirmation to prevent the user adjusting the black level 
too low, since the two shades displayed remain discernible at all 
brightness settings above the correct one. 
In the professional studio engineering environment, test signal generators 
are known in which an area below black level is included adjoining a black 
area in addition to an above-black (grey) area. See for example Quinn and 
Siocos: "Pluge Method of Adjusting Picture Monitors in Television 
Studios--A Technical Note", Journal of the SMPTE Vol. 76 p 925 (September 
1967). In such a case, the setting is correct when the above-black level 
is discernible, but the black and below-black areas are indistinguishable. 
Such test patterns are also commonly recorded before program material on 
video tapes in professional environments. Such a test pattern is not known 
to have been broadcast or included in a domestic television set or video 
recording, however, and in any event its significance and the manner of 
its exploitation are not readily appreciated by the average professional 
or domestic user. 
SUMMARY OF THE INVENTION 
It is an object of the invention to facilitate an accurate and optimum 
setting of display device adjustments such as brightness in an intuitive 
manner. 
The invention provides a video signal processing apparatus comprising means 
for generating video signals to enable the display of still or motion 
pictures on a connected display device, and means for generating a test 
signal to enable the display of a test image to facilitate user adjustment 
of a property of the display device to a correct setting which provides 
optimum representation of the said pictures, characterized in that the 
test image includes a first image feature imperceptible at the correct 
setting, but visible when the display device deviates in a given direction 
from the correct setting, and in that the first image feature when visible 
forms at least part of a symbolic instruction to the user indicating the 
nature of the deviation and/or the necessary corrective adjustment. 
The invention enables, by simple means, the provision of dynamic on-screen 
instructions to the user, these instructions indicating the necessary 
adjustment and being apparently responsive to the user's adjustments by 
disappearing when the setting is correct. The instructions may be formed 
by shaping the first image feature to form words or pictograms, so that 
the necessary adjustment is immediately apparent even to a user unfamiliar 
with the apparatus, without reference to an instruction manual or other 
training. 
Various settings may be effected in this way. Where the video signals 
include luminance information ranging upward from a black level, the first 
image feature may comprise a first regions at black level adjoining a 
second region at a level below black level respectively, these regions 
being represented in the test signal but being indistinguishable in the 
test image when displayed at the correct setting of the black level in the 
display device. The instruction conveyed by the first image feature in 
that case should prompt the user to reduce the brightness setting of the 
television or other display device. 
The test image may further include a second image feature which is just 
visible at the correct setting, but becomes imperceptible in the event of 
excessive corrective adjustment. This second image feature may be at a 
similar level to the feature proposed in DE-A-2 716 212, and complements 
the functioning of the first image feature by preventing over-correction 
by the user in response to the first image feature. 
The test image may be generated automatically in response to a user 
commencing adjustment of the display device brightness or other property. 
Where the video signal generating means comprises means for reproducing 
still or motion picture sequences stored on a record carrier, the test 
signal generating means may operate automatically to facilitate adjustment 
of the display device prior to viewing, or it may operate at user 
selection only. 
Where the pictures to be displayed are stored pictures, as for example on a 
video cassette, interactive video disc or CD-ROM, then it may be 
advantageous for the test signal to be defined by information stored on 
the record carrier itself. In particular, this has the advantage that the 
invention can be implemented using for the most part conventional display 
apparatus hardware. 
Accordingly, the invention further provides a method of storing pictures on 
a record carrier for subsequent reproduction via a display device having 
at least one user-adjustable display property, the method comprising: 
(a) storing picture information on the record carrier in a form suitable 
for reproduction by the display device; 
(b) defining a test signal suitable for causing the display of a test image 
including a first image feature imperceptible at a display property 
setting which is correct for the display of the stored pictures but 
visible when the display property deviates in a given direction from 
correct setting; and 
(c) storing information defining the test signal on the record carrier 
together with the picture information, characterized in that the first 
image feature, when visible, forms at least part of a symbolic instruction 
to the user indicating the nature of the deviation and/or the necessary 
corrective adjustment. 
To facilitate a brightness setting adjustment, the step (b) may include: 
identifying a range of luminance values to be represented in the display of 
the recorded pictures, said range extending upwards from a black level; 
defining as the first image feature a first region at the black level 
adjoining a second region at a level below the black level respectively, 
these regions being represented in the definition of the test signal. 
The step (a) may comprise endcoding digitized photographs and storing the 
resulting code on the record carrier. While it would be possible to store 
the test image as a digitized photograph, processed as necessary to obtain 
levels outside the "legal" range, it may be simpler if the step (c) 
comprises storing code for configuring the display apparatus to generate 
the test signal synthetically. 
The invention yet further provides a record carrier whereon pictures have 
been stored by a method in accordance with the invention as set forth 
above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The invention can be applied in a wide range of display systems, from 
simple domestic television sets, through VCRs, video disc and interactive 
disc players to high-end graphics workstations. In all these devices there 
is a desire to ensure that the display device adjustments, such as 
brightness, color and contrast, are adjusted regularly to take account of 
various viewing (lighting) conditions. Only then is it certain that the 
limited dynamic range (for example) of the display device, be it a CRT, 
LCD or whatever, is exploited fully in the representation of photographic 
and other images. By way of example only, the Figures present an 
embodiment in the form of an interactive video application using the 
Compact Disc-Interactive (CD-I) standard. 
FIG. 1 is a block schematic diagram of the compact disc-interactive (CD-I) 
player. It comprises a compact disc player CDP to which is connected a 
compact disc digital audio controller decoder CDDA and a compact disc 
control unit CDCU. The CDDA is connected to an audio processing unit APU 
which feeds two loudspeakers LSL and LSR. The CD control unit CDCU is 
connected to a system bus SB along which various digital signals are 
passed. Also connected to the system bus SB are a microprocessor unit MPU, 
a DMA controller DMA, a non-volatile random access memory NVRAM, a clock 
calendar unit C/C, a read-only memory containing the real-time operating 
system CD RTOS, a keyboard KB, a pointing device INP, and an access 
controller AC. The access controller controls the reading from and writing 
to a random access memory RAM which is split into two banks zero and one. 
The access controller is also connected to a video decoder VD which in 
turn feeds a video generator VRGB, the output of which is connected to a 
video display unit VDU. Also connected to the system bus SB is an adaptive 
pulse code modulation decoder ADPCM which feeds the audio processing unit 
APU. A description of the CD-I base case decoder as shown in FIG. 1 is 
given in a text book entitled "Compact Disc-Interactive, A Designer's 
Overview" edited by Philips International and published by Kluwer 
Technical Books, ISBN 920121103. 
The video decoder VD in the CD-I player can read picture information which 
has been transferred from a compact disc (CD-ROM) to the random access 
memory RAM, which leads to the generation of appropriate video signals for 
the VDU by the video generator RGB. The Philips/Kluwer book describes how 
various picture coding formats are available. In particular, a mode called 
DYUV (`Delta-YUV`) provides compact DPCM coding of natural colour 
photographs. A further mode is proposed for use in the production versions 
of CD-I, using Discrete Cosine Transform (DCT) coding to achieve data 
compressions high enough for full-screen, full-motion video pictures. 
Other coding modes, using a color look-up table (CLUT) in the decoder VD, 
allow coding of synthetic graphics and text images containing a limited 
range of colors. For all these modes, a standard 8-bit range of levels 
(0-255) is adopted for each of red, green and blue. In accordance with 
CCIR recommendations, black level is defined as 16, not zero, and peak 
white is defined as 235, not 255, to allow for some overshoot in the 
processing of the video signals. 
The levels 0-16 should all appear uniformly black if the brightness of the 
VDU is correctly adjusted, but the codes 0-15 (below black level) are 
nonetheless represented by lower R,G,B signal levels in the video output 
signal. This allows the decoder VD and video generator VRGB to be used as 
a test signal generator in accordance with the invention, by the inclusion 
of suitable configuring information on a CD-I disc, or in the read-only 
memory CDRTOS. In other types of display apparatus, some specific hardware 
provision may be required to generate the test signal, but this need not 
be expensive, and is well within the capabilities of the person skilled in 
the art. 
FIG. 2 shows in its top and bottom halves two test images that may be 
generated to facilitate accurate brightness setting in accordance with the 
invention. In both images, a background area 100/100' is at black level 
and must therefore be imagined by the reader to be in fact black when 
displayed correctly. In conjunction with the black background 100/100', a 
first image feature is defined by a region or regions 102/102' which are 
at a level just below black. A second image feature is defined in each 
test image by the background 100/100' in conjunction with a region 
104/104' which is at a grey level slightly above black. 
A CD-I disc loaded into the player of FIG. 1 contains a large number of 
photographic images stored in DYUV form as described in the Philips/Kluwer 
book, to be retrieved, decoded and displayed by the CD-I player as part of 
an interactive audiovisual presentation. The test image of FIG. 2 (top 
half, or bottom half) is displayed by the player in a compulsory or 
user-selected start-up phase of the presentation, prior to display of the 
stored photographs. When the VDU brightness setting is correct, the second 
image feature 100/104 is just discernable by the user on the VDU screen, 
while the first image feature 100/102 is not. 
If the brightness is set too high, however, then the levels below black 
level in the video test signal which defines the test image will be 
represented on screen, so that the first image feature is visible to the 
user. 
The first image feature 100/102 in the FIG. 2, top half, forms the words 
"TOO BRIGHT", which inform the user that the brightness is set too high. 
The user is therefore instructed by the test image to decrease the 
brightness until the correct setting is reached, at which point the works 
"TOO BRIGHT" will disappear from view. If the user raises the brightness 
beyond the correct setting, the second image feature 100/104 will also 
disappear, informing the user accordingly. The user can then correct 
downwards until the second image feature 100/104 is again discernable. The 
user then knows that the brightness setting is at the correct level. The 
second image feature 100/104 corresponds to the black and grey areas in 
the test pattern proposed in DE-A-2 716 212, mentioned above. In that 
known pattern, the background is grey while the center is black. It will 
be appreciated that the test images described herein will work just as 
well in this inverted form. DE-A-2 716 212 offers guidance on the minimum 
size for these image features, relative to the screen size, which can be 
used to avoid dazzling by other, brighter parts of the image. 
In FIG. 2, lower half, the first image feature 100'/102' is a pictographic 
instruction to decrease the brightness setting, in the form of a downwards 
arrow. This may be a preferable form of instruction for a product in an 
international market, but it should be noted that a CD-I player for 
example, may be aware of the language being used for user interaction, and 
could store literal instructions such as "TOO BRIGHT" in a number of 
languages, reproducing the appropriate one at each occasion. 
The lower half of FIG. 2 also includes two further downward arrow-shaped 
regions 106' and 108', which are two and three levels below black level, 
respectively. Thus the number of down arrows visible given the user an 
indication of the extent of the just how far from the correct setting the 
brightness setting actually is. 
FIG. 3 illustrates how one representative line of pixels in the test image 
of FIG. 2, lower half, may be encoded to cause generation of the 
appropriate test signal. 7-bit run-length CLUT coding has been chosen from 
the range of techniques available in the CD-I video decoder VD. This is a 
compact format, but any of the other formats could be used. The first task 
is to load the color look-up table with the red, green and blue values 
defining each of the color used in the desired test image. An example is 
shown in Table 1. 
TABLE 1 
______________________________________ 
CLAD R G B 
______________________________________ 
0 16 16 16 
1 12 12 12 
2 8 8 8 
3 4 4 4 
4 20 20 20 
5 24 24 24 
6 28 28 28 
. . . . 
. . . . 
. . . . 
127 -- -- -- 
______________________________________ 
The first column CLAD in Table 1 is a 7-bit CLUT address in the range 
0-127. The CLUT address CLAD then acts as an index to the three 8-bit 
values R, G and B that define the color indexed by that address. In Table 
1, R=G=B for all table entries, since only neutral tinted greys are to be 
reproduced. In general use, the CLUT can address a color gamut of more 
than 10 million colors. 
For the first CLUT entry, CLAD=0, R,G,B=16, meaning that CLAD=0 represents 
the color black, used for the background region 100'. CLAD=1, 2 and 3 
represent the three levels below black used in the arrow regions 102', 
106' and 108', respectively. Although in the 8-bit coding scheme 
described, the three levels closest below black (16) are 15, 14 and 13, 
the CLUT locations 1, 2 and 3 have been loaded with values R,G,B=12, 8 and 
4, respectively, for two reasons. One reason is that, in the CD-I player 
specification (`base case decoder`), it is only necessary for the analog 
video output signals R, G and B to be generated to 6-bit accuracy (64 
levels). Thus, although 8-bit values are stored on the disc and within the 
player, the output D/A converters might convert only the six most 
significant bits of each color value. Thus two color values must be 
separated by at least four levels on the 8-bit scale to ensure that they 
are in fact distinguishable in the video output signal. The second reason 
for using steps of 4 levels is that, even if the video output is generated 
to 8-bit accuracy, the user's eye would have difficulty discerning the 
features of the test image if they were separated by only one level. 
Moreover, the brightness adjustment on the display device may be too 
coarse to allow adjustment with 8-bit precision. Similarly, for CLAD=4, 
the CLUT is loaded with R,G,B=20, to be used as the first grey level above 
black, in region 104'. 
The line L in FIG. 2 indicates a one representative scanline (pixel row) of 
the test image which is run-length coded as now described with reference 
to FIG. 3. The line L is at normal resolution 384 pixels long and it is 
assumed for the purposes of this example that the line L comprises, from 
left to right: first a run of 90 pixels at black level (background region 
100'); next a run of 10 pixels at 3 levels below black (region 108'); 30 
pixels at black level; 10 pixels at 2 levels below black (region 106'); 30 
pixels at the level below black (region 102'); 40 pixels at black level; 
18 pixels at the grey level above black (region 104'); 45 pixels at black 
level; 18 pixels at the grey level above black (region 104'); and finally 
83 pixels at black level. These eleven runs are represented by a sequence 
of number pairs at 300 in FIG. 3. The CD-I standard specifies that a pair 
of bytes can be used to represent a run of up to 255 pixels, and this 
format is used in FIG. 3 as follows. 
A representative byte pair 301,302 is shown in FIG. 3. The first byte 301 
comprises a first bit R, which is set at 1 to indicate that run length 
coding is being used (R=0 indicates coding of an individual pixel). The 
remaining 7 bits of the first byte contain the CLUT address CLAD where the 
desired color has been stored. In the example, CLAD is binary 0000011, or 
3 in decimal. The second byte 302 stores in binary RL, the run length. In 
the example, this is binary 00001010, or 10 in decimal. Thus the byte pair 
shown defines a run of ten pixels, with color CLAD=3, in other words, the 
part of region 108' lying on line L. 
Each run of pixels in a particular colors is represented by a similar byte 
pair, so that the sequence 300 of eleven number pairs can be encoded in 22 
bytes for decoding by the video decoder VD. The last run of black pixels 
is encoded with a run length byte RL=zero, which tells the decoder VD that 
this run is the last on the line and continues to the end of the line. 
Those skilled in the art will readily appreciate the wide variety of test 
images that are possible within the scope of the present invention. The 
second image feature 100/104 could be made to form a more explict 
`correct` symbol when seen alone. Background and foreground colors may be 
reversed, and flashing colors or other animation effects can be used to 
improve visibility of the various regions if desired. In the CD-I 
embodiment described, these effects can be achieved simply by modifying 
the CLUT entries, rather than storing multiple test images. In a CD-I 
application, the storage space occupied by the necessary program can be 
only a few kilobytes out of the total of 600 Mbytes available, while the 
improvement in ease of use and the picture quality can be substantial. 
The skilled reader will readily appreciate how the invention can be applied 
in other types of display apparatus than the CD-I player. In a television 
receiver, the test signal generator could be readily incorporated for 
example in the on-screen display hardware which is already incorporated in 
many modern televisions, or in a teletext decoder. The test image would 
preferably appear on the screen or a part of it automatically when the 
brightness control is activated. In a VCR, a test signal generating 
circuit could be included in a similar manner. Alternatively, a display 
apparatus according to the invention could be made from an existing VCR by 
if the test signal is recorded on a video cassette tape. The test signal 
might for example be recorded for a few seconds at the start of a 
commercial pre-recorded video cassette, enabling the viewer to ensure 
correct adjustment of his/her television brightness before the start of 
the recorded program. The skilled reader may also conceive similar test 
signals for the correct setting of other display device properties, for 
example contrast, color or picture sharpness. 
From reading the present disclosure, other variations will be apparent to 
persons skilled in the art. Such variations may involve other features 
which are already known in the design, manufacture and use of display 
systems and devices and component parts thereof and which may be used 
instead of or in addition to features already described herein. Although 
claims have been formulated in this application to particular combinations 
of features, it should be understood that the scope of the disclosure of 
the present application also includes any novel feature or any novel 
combination of features disclosed herein either explicitly or implicitly 
or any generalisation thereof, whether or not it relates to the same 
invention as presently claimed in any claim and whether or not it 
mitigates any or all of the same technical problems as does the present 
invention. The applicants hereby give notice that new claims may be 
formulated to such features and/or combinations of such features during 
the prosecution of the present application or of any further application 
derived therefrom.