JPS6258194B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to display systems. 2
Level display systems employ a display panel consisting of a matrix of closely spaced display cells that can assume either of two light emitting states.
That is, each display cell is either fully excited (on) or not excited at all (off). Images and other graphical data can be displayed on the two-level display panel by selectively exciting the cells. Because each cell in a two-level display panel is either fully on or completely off, the panel inherently has the ability to display a gray level (intermediate brightness) of the image to be reproduced. do not have. However, it is known that the impression of gray levels can be reproduced using a technique known as "dithering". In so-called "dizard display systems", by appropriately arranging on and off cells, the viewer perceives different gray levels, ie different brightnesses. Dithering is accomplished in two-level display systems by dividing the image to be reproduced into a matrix of pixels, each pixel being associated with a cell in the display panel. Each display cell is assigned a predetermined dither threshold. The intensity (brightness) of a certain pixel is
A cell is turned on if it is greater than the dither threshold assigned to the corresponding cell. Otherwise the cell is kept off. A dithered display system capable of displaying moving images could theoretically be implemented by dithering image frames in sequence at a speed sufficient to avoid flickering to the eye. A “write” or “excitation” signal is applied to each cell to be turned on in a frame;
An "erasure" or de-excitation" signal is applied to the cells that are to be turned off in that frame. However, in such video techniques, it is difficult to determine whether the state of a cell in one frame is different from the state in the previous frame. Unfortunately, the write or erase signals must be sent very frequently as the cells are accessed regardless of the speed of some two-level display panels, particularly plasma display panels, which are the most readily available on the market. is not fast enough to accommodate the large number of accesses per second required to display good moving images; two-level display panels that can do this are extremely expensive. a plurality of two-level display regions, each of which is excited and de-excited, each corresponding to a pixel of the image to be displayed; and a region which is in a non-excited state, and the intensity of the corresponding image pixel is related to that region. only each of the display regions is in a first predetermined relationship with the threshold level associated with the region and the intensity of the region in the excited state and the corresponding pixel is in a first predetermined relationship with the threshold level associated with that region. and means for accessing only each of the related display areas. The display areas are configured as a matrix including a plurality of submatrices in the form of n areas by n areas. , and regions in each of the submatrices are assigned different threshold levels, derived from a threshold matrix D _o common to the submatrices, where n is an integer power of 2; D _o is a matrix k [4D _o/2 ], k [4D _o/2 + U _o/2 ], k [4D _o/ 2 ] in 2×2 format.
+2U _o/2 ] and k[4D _o/2 +3U _o/2 ], D ₂ is a 2×2 matrix consisting of the numbers “0”, “1”, “2” and “3”, and U _o/2 is an n/2×n/2 matrix with all elements being “1”,
k is a predetermined scalar constant. The access means is configured to access only those areas of the display which are in an unexcited state and for which the intensity of the image pixel corresponding to that area exceeds an upper threshold level greater than the threshold level associated with the area, and which are in an excited state. The display is configured to access only those display areas that are located in a region where the intensity of the image pixel corresponding to the area is below a lower threshold level that is less than the threshold level associated with the area. The access means includes a memory for storing a plurality of bits, each of which corresponds to a display area and indicates whether or not this area is excited; generating a first signal in response to being in a first predetermined relationship with an associated threshold level, and wherein the intensity of each image pixel is in a first predetermined relationship with an associated threshold level; In response to the fact that the level has a second predetermined relationship, the second
a first signal is present and indicates that the bit in the memory is in the non-excited region; and a second signal is present and the bit in the memory is in the excited region; and means for generating a signal for accessing the area. The access means includes another memory for storing a signal indicative of the threshold level, and the means for generating the first and second signals corresponds to the stored threshold level for each image pixel intensity. and a comparator for generating first and second signals in response to whether the intensity of the pixel is greater or less than the threshold level. The access means stores a signal representative of the threshold level if only the display areas in the unexcited and excited states are accessed when the intensity of the corresponding image pixel is greater or less than the upper or lower threshold, respectively. and adding or subtracting values to the signal stored in the separate memory depending on whether the corresponding bit stored in the memory indicates whether it is in the non-excited or excited region. and means for generating the first and second signals for comparing the intensity of the image pixel with the associated upper or lower threshold level. includes a comparator,
Is the pixel intensity greater than the upper threshold level?
Alternatively, the first or second signal is generated depending on whether the lower threshold level is lower than the lower threshold level. It is advantageous if the difference between the upper and lower threshold levels is variable. Means may also be provided for increasing the value added to or subtracted from the signal stored in another memory in response to the frequency of access to the display area exceeding a predetermined level. The invention will become more clearly understood by an example with reference to the accompanying figures. FIG. 1 shows a video dither display system, which includes a camera 10, a signal processor 4
0 and 2 level display panels 70 are included. Panel 70 may be a plasma display panel, such as that shown in US Pat. No. 3,671,938. However, the invention can be implemented with any type of two-level display panel. Panel 70 includes 4096 display areas or display cells arranged in a matrix of 64 rows and 64 columns. It goes without saying that the number of display cells is merely an example.
Each cell of the two-level display panel 70 has two
It can be in one of two states: fully excited and on, or completely unexcited and off. The lower right portion of panel 70 is shown enlarged in FIG. Each cell is assigned a dither threshold value taken from a predetermined 16-element "dither matrix" as follows: As shown in FIG. 2, panel 70 can be viewed as being divided into a plurality of submatrices, each containing 16 cells. Each cell within any submatrix is given a different threshold value taken from the dither matrix above. This dither matrix can be used depending on the purpose of use.
larger ones containing more than 16 elements,
Alternatively, a smaller one can also be used.
Increasing the number of cells per dither matrix allows increasing the number of gray levels without reducing image resolution. Conversely, reducing the number of cells per dither matrix limits the gray levels. For best results, numerically consecutive thresholds within a dither matrix, regardless of their size, should be spatially separated from each other within the matrix. When n is an integer that is a power of 2, the dither matrices D _o of n cells x n cells that satisfy the above conditions are generally four matrices k [4D _o/2 ], k [4D _o/2 + U _o/2 ],k
It is known that it can be constructed by arranging [4D _o/2 + 2U _o/2 ] and k [4D _o/2 + 3U _o/2 ] in a 2x2 manner as follows. This is obviously a recursive definition, and when n = 2, D ₂ is the number “0”, “1”, “2” and “3”.
2x2 matrix containing

[Formula], U ₂ is a 2×2 matrix in which all elements are “1”, and k above is a predetermined scalar constant. The 16-element dithering matrix _D4 used in the display system shown in Figure 1 has k
16 by applying the above definition. 64-element dither matrix if needed
D ₈ is also obtained by applying the above definition to the dither matrix D ₄ . Although not necessarily required, matrices k[4D _o/2 ] and k[4D _o/2 +U
_o/2 ] is preferably on the diagonal of the dither matrix D _o , and it is also desirable that the numbers "0" and "1" of the matrix _D2 are also on the diagonal within _D2 . The image to be displayed on the panel 70 is scanned in a fixed format and decomposed into 4096 pixels arranged in 64 rows and 64 columns. Thus, each scanned pixel corresponds to one of the cells of panel 70.
In this example, the light intensity of each pixel is quantized into 256 intensity levels. The quantized intensity level of each pixel is compared to the dither threshold assigned to the corresponding display cell. At this time, if the intensity level is greater than the dither threshold assigned to the cell, the cell is turned on. Conversely, if the pixel's intensity level is less than or equal to the dither threshold assigned to the cell, the cell will remain off. FIG. 3 shows an example of the intensity of some pixels of an image to be displayed on the panel 70. These pixels correspond to cells in the lower right portion of panel 70 in FIG. FIG. 4 is an enlarged view of panel 70 showing the dithered image with selected cells excited. The white areas in FIG. 4 represent cells that are turned on. Similarly, black portions correspond to cells that are off. The pattern of on and off cells in the lower right portion of FIG. 4 is obtained by comparing the pixel intensity value pattern of FIG. 3 with the dither threshold shown in FIG. When looking at the image of panel 70 in FIG. 4 at a distance, it is apparent that the image exhibits various gray levels, which are the result of the dithering described above. The circuit of FIG. 1 for displaying a dithered image on a panel 70 by the method described above includes a camera 10 and a signal processor 40, which includes a clock 11 and an analog-to-digital converter 12. ,
It includes an address register 15, a 16-word read-only memory ROM 16, a comparator 21, and an address register 45. The image to be displayed is scanned by camera 10, and the image is decomposed into a matrix of 4096 pixels arranged in 64 rows and 64 columns. Scanning starts from the top row and goes from left to right in each row. Camera 10 generates an analog signal representing the intensity of the pixel being scanned. A signal representing the intensity of the pixel is sent to the camera 10 by periodic pulses from the clock 11.
The signal is then sent to the analog-to-digital converter 12, where it is quantized into a 256-level signal. A multi-bit binary signal representing this level is sent via lead 13 and cable 14 to comparator 21. Pulses from clock 11 are also sent to address register 15. Register 15 includes an 8-stage binary counter, which is clocked by clock 11.
It is advanced by one count by the clock from . Two lower address read 16 of ROM16
A is connected to the outputs of the lower two stages of the register 15. The two upper address leads 16B of the ROM 16 are connected to the outputs of the two upper stages of the register 15. The 16 dither thresholds assigned to each cell within each submatrix of panel 70 shown in FIG.
8, 32, 160, 192, 64, 224, 9
6,48,176,16,144,240,11
They are stored in the order of 2,208,80. As is clear from this, from clock 11
Each time a group of 256 consecutive pulses is applied, the output from ROM 16 is first 0, 128,
The column of 32,160 is repeated 16 times, then 192,64,
224, 96 repeated 16 times, followed by 48, 176, 16, 144
is repeated 16 times, and then 240, 112, 208, 80 are repeated 16 times. This threshold value column is the output lead 1 of ROM16.
7 in decimal format and applied to the comparator 21 via the cable 18, cable switch 22, and cable 24. As described above, the quantized intensity value of each pixel and the panel 7
The dither threshold assigned to the 0 cell is applied to comparator 21 at the same time. The output of comparator 21 is a 1-bit binary signal and is applied via lead 26 to data input terminal DT of panel 70. If the intensity value on cable 14 is greater than the dither threshold on cable 24, the signal on lead 26 will be a "1". This "1" indicates that the cell corresponding to the pixel currently being scanned should be turned on. Circuitry within panel 70 applies a "write" or "excite" signal to this cell. On the other hand, when the intensity signal on cable 14 is less than or equal to the dither threshold on cable 24, the signal on lead 26 will be a "0" indicating that the cell should be turned off. In this case, an "erasure" or "de-excitation" signal is applied to that cell. A multi-bit binary code indicating the location of the cell corresponding to the pixel currently being scanned is applied from address register 45 via lead 61 and cable 46 to address input AD of panel 70. The register 45 is, for example, a 12-stage binary counter, and each time a pulse is applied from the clock 11,
You can only proceed. The top 6 bits of lead 61 and
The lower 6 bits specify the row and column of the cell in question. Animated dithered images are created in a dithered display system such as that shown in FIG. 1 by simply scanning successive frames of the image and accessing the display panel by a "write" or "erase" signal as described above. It can be displayed by However, as mentioned above, it is impractical to use such video techniques in display systems using cells with slow access speeds. This is because each cell must be accessed every frame. panel 70
For example, it is assumed that the cell contains such a cell. However, the dither display system of FIG. 1 is capable of displaying such moving images through conditional access circuitry. In other words, “excitation” or “deexcitation” in any given frame
The only cells that are accessed to receive the signal are those whose state in that frame is different from the state in the previous frame. Other cells are not accessed at all, but their previous on or off state remains intact. When displaying various types of animated dithered images, such as faces, only a small number of cells change their state in successive frames. Therefore, when implementing conditional access techniques such as those described above in plasma display systems or other display systems with low access speed cells, successive frames of a video dithered image appear smooth and continuous. can be displayed at a sufficient frame rate. A circuit that realizes a moving image using the conditional access technique as described above includes an exclusive OR circuit 41, a delay device 42, and a frame memory 50.
Frame memory 50 can store 4096 bits, each corresponding to each display cell of panel 70. The value of each bit in memory 50 represents the current state of the corresponding cell. That is, "1" indicates on and "0" indicates off. Memory 50 operates in response to signals on output enable lead 52 and generates signal bits on data output lead 51 indicating the state of the cell indicated by the address on cable 46. The signal on output energization lead 52 is obtained by passing pulses from clock 11 through delay device 42. This is to allow the state of address register 45 to "settle" before retrieving the data output from memory 50. Assume now that the first frame of a moving image has been displayed on panel 70 in the manner described above, and that camera 10 has begun scanning the next frame. As before, the signal on lead 26 indicates the state of the cell corresponding to the pixel currently being scanned. The signal on cable 46 also indicates to panel 70 the location of that cell. However, this cell will not be accessed, nor will a "write" or "erase" signal be applied, unless a binary signal of value "1" is applied to the state change terminal CS of panel 70. A signal to the state change terminal CS is generated by the exclusive OR circuit 41 and sent to the panel 70 via the lead 43.
is applied to Exclusive OR circuit 41 is lead 2
6 and 51. Therefore, exclusive OR circuit 41 generates a binary "1" on lead 43 only if the state of the cell corresponding to the currently scanned pixel is different between the first and second frames. If the state is different, the cell indicated by the address on cable 46 is accessed in panel 70 and its state is changed to that indicated by lead 26. The signals on leads 26 and 43 are also connected to data input lead 47 and input enable lead 48 of memory 50, respectively. When the signal on lead 48 is a "1", the signal on lead 47 indicating the new state of the cell is written to the appropriate memory location in memory 50. Although the memory system of FIG. 1 operates in the manner described above to display the scanned image for each frame of the motion picture, it is not necessary that all cells of the display panel be accessed for each frame. Although this conditional access technique is effective in slow dither display systems, it also generally exhibits undesirable effects in dither display systems. The effect is a random flicker or scintillation across the cells of the display. Scintillation in a motion picture dither display occurs, for example, when a relatively constant pixel intensity value is very close to the dither threshold assigned to the corresponding cell. That is, in such a case, when the noise signal in the display is superimposed on the intensity signal, it will randomly become larger or smaller than the threshold for each frame, resulting in random scintillation of the cells. The nature of this scintillation effect is the fifth
This is clear from the figure. Figure 5 shows a single pixel.
The signal IS is shown representing the intensity in successive frames. As shown in FIG. 5, a small amplitude noise component is superimposed on the signal IS. Also, the conventional or “nominal” dither threshold assigned to the cell corresponding to the above pixel is “160”.
It's getting old. The signal IS is scanned or sampled once per frame at fixed positions in the frame. In FIG. 5, this scan position is indicated by the position of the frame number shown on the horizontal axis. The exact value of the signal IS at this scan position is indicated by the black circle. At the scan positions of frame numbers 1, 2, and 5-9, the value of the intensity signal IS is smaller than the dither threshold "160". Therefore, line 1 at the bottom of Figure 5
As indicated by 01, the cell is off in these frames. In frames 3 and 4 the strength signal IS is greater than "160" and the cell is on in these frames. In frames 10-15, the average value of signal IS is only slightly less than the dither threshold. However, since noise is superimposed on this, the threshold is crossed several times in frames 10-15, causing scintillation at random intervals. Various methods can be taken to reduce this scintillation. One is that the cell does not change state unless the pixel's intensity remains on one side of the threshold for a certain number of frames, say two frames. Furthermore, in response to changes that would not change the average intensity in a region near the cell in question in other methods, a method is used in which the state of the cell is not changed. However, a scintillation reduction technique that is simpler than any of the above and has at least the same effect is the so-called "hysteresis dither threshold method." In this method, a width with hysteresis is set for each dither threshold. This width is limited by upper and lower thresholds on either side of the nominal value. Cells that are turned off are turned on only when the intensity of the corresponding pixel exceeds the upper threshold. A cell that is on will only turn off when the intensity of the corresponding pixel becomes less than the lower threshold. As shown in FIG. 5, the upper and lower thresholds are set at positions "164" and "156" above and below the nominal dither threshold "160", respectively. The cell in question is turned off in frames 1 and 2, as indicated by 102 at the bottom of FIG. In frame 3, even though the signal IS is above the nominal threshold, the cell remains off because the signal IS is less than the upper threshold. However, in frame 4, the cell is turned on. 1
Once the cell is turned on, it will not turn off until the signal IS is less than the lower threshold. Thus, in frame 5, the cell is on even though the signal IS is less than the nominal threshold. However, in frame 6 the signal IS becomes less than the lower threshold and the cell is turned off. Frames 7 to 1
5, the signal IS never exceeds the upper threshold, so the cell remains off. frame 10
The random scintillation mentioned above in -15 is thus removed. Direct implementation of such a hysteresis dither threshold method requires two bits per pixel (ie, one cell). That is, one bit stores the current state of the cell to determine whether the state of the cell in the current frame is the same as the state in the previous frame. Other bits store whether the pixel's intensity signal is to be compared to the upper or lower threshold. However, in the video day display, 1
A hysteresis dither threshold method can be implemented with only one bit of memory per pixel. Circuitry for this purpose is included in the embodiment of the dither display system of FIG. 1 and includes cable switch 22, adder/subtractor 31, hysteresis register 32, and inverter 34.
This circuit operates when the switch 22 is in the position of the output lead 35 of the adder/subtractor 31 rather than the output of the ROM 16. Hysteresis register 32 includes, for example, a binary counter and generates a multi-bit binary signal on lead 33 and cable 38. This signal provides a predetermined number that is added to or subtracted from the nominal threshold to provide the upper and lower thresholds. In this example, this number is binary "100", or decimal "4". Cable 38 is connected to one data terminal of adder/subtractor 31. A cable 18 is connected to the other data terminals. Adder/subtractor 31 adds the numbers on cables 18 and 38 when "1" and "0" are applied to the "10" and "1" control terminals, respectively. These numbers are subtracted if the inputs to the control terminals are reversed. The decision whether to compare the intensity of a given pixel to the upper or lower dither threshold depends on the current state of the corresponding cell. As mentioned above, the first
The current state of each cell in the illustrated display system is stored in frame memory 50 and appears on lead 51 when the pixel corresponding to that cell is scanned. As shown in FIG. 1, the "+" and "-" control terminals of the adder/subtractor 31 are
The bit above 1 is applied. In other words “-”
The terminals are connected directly to the lead 51, and the "+" terminal is connected to the lead 51 via the inverter 34. When the cell corresponding to the pixel currently being scanned is on, a "1" appears on the lead 51 and is applied to the "-" terminal of the adder/subtractor 31. At the same time, "0" is applied to its "+" terminal. The resulting number on cable 38 is subtracted from the nominal threshold on cable 18. The comparator 21 thus compares the quantized intensity value of the pixel being scanned with the lower threshold assigned to the corresponding cell. Conversely, when the cell corresponding to the pixel being scanned is off, "1" and "0" are added to the adder/subtractor 31.
is applied to the "+" and "-" terminals of the "+" and "-" terminals, respectively.
This results in the numbers on cables 18 and 38 being added. Comparator 21 compares the quantized intensity value of the pixel being scanned with the upper threshold value assigned to the corresponding cell. The conditional access technique in the display system of FIG. 1 reduces the number of cells accessed per frame as described above, but the cells accessed in a given frame are randomly distributed on the panel. They may be clustered in a relatively small part of the frame period instead of all over the place. This is because the movement of the displayed image is limited to one part, such as the mouth of a person speaking. In such a case, even if there are few cells, it may not be possible to access them quickly enough. Thus, the circuitry within panel 70 includes a conventional first-come, first-serve buffer (not shown) to store data and address information until the cell is accessed. In addition to such buffers, the display system of FIG. 1 may include circuitry to vary the width of the dither threshold hysteresis to accommodate an unusually large number of cell state changes per frame. Although this method degrades the image quality to some extent, it has the advantage of reducing the number of cells that must change state in each frame. Overflow leads 71 from panel 70 are for this purpose. A first signal is applied to overflow lead 71 when the cell state change rate has reached a predetermined level, as indicated by, for example, the amount of data in the buffer in panel 70. This signal increases the count value of hysteresis register 32, thereby expanding the hysteresis width. When the overflow in the buffer in panel 70 is eliminated, a second signal appears on lead 71, and the count value in register 32 is restored to its original value. In the display system of FIG. 1, the state change signal on lead 43 is connected to panel 70, but this signal is used only within processing unit 40 and is used to gate data and address information to the display panel. It is clear that it is possible. In such an arrangement, a data bit and corresponding address sent to the display panel indicates that the state of the specified cell is to be changed. It is clear that conditional access techniques reduce the amount of information bits that must be applied per unit of time to display an animated dithered image on a display panel. The bandwidth for transmitting such image information to the panel is also decreasing. Additionally, the hysteresis dither threshold method described above reduces the number of information bits that must be transferred to the panel. Furthermore, although the above description has been made regarding the display of monochromatic images and moving images thereof, it is clear that dithering can be used to display only a single frame or to display moving images in color.
In such a case, each cell of the display panel would consist of a plurality of display elements, each of which would emit a different color (for example, three elements would emit red, green, and blue). Similar to monochromatic dither display systems, these dither display elements can be either fully on or
There are only two states: completely off. When the image to be reconstructed is being scanned, three intensity signals are produced for each pixel. Each of these intensities represents the intensity of one of the three colors at the pixel. Each intensity value corresponding to a cell is compared to a dither threshold assigned to the cell. For intensity signals that exceed the dither threshold, the corresponding display elements in the corresponding cells are excited. Conversely, display elements corresponding to intensity signals that do not exceed the dither threshold are turned off. The color image obtained as a result is good and can also be made into a moving image. The display element within each cell is
It can only be in either the on or off state, but
The strength and color of the image will be good.

[Brief explanation of the drawing]

FIG. 1 shows a dithered
2 is a block diagram of a display system, FIG. 2 is an enlarged view of a portion of a display panel used in the display system of FIG. 1, and FIG. 3 is a block diagram of a display system shown in FIG. FIG. 4 is an example of a map of the pixel intensity of a part of an example of an image to be displayed. FIG. 4 is an example of a display panel used in the display system of FIG. The display system shown in Figure 1 shows the temporal change in intensity of one pixel of a moving image. Explanation of the main parts of the drawing, display area...
Cells in panel 70 in FIG. 1, access means...
Signal processor 40 in FIG. 1, threshold matrix D
_o ...Matrix within the submatrix of Figure 2,
Memories...memory 50 in FIG. 1, means for generating the first and second signals...comparator 21 in FIG. 1, means for generating signals...gate 41 stage in FIG. 1, another memory... ...ROM 16 in FIG. 1, comparator...Comparator 21 in FIG. 1, means for setting a threshold level...Adder/subtractor 31, hysteresis register 32 and inverter 34 in FIG. 1, means for increasing a value... ...Panel 70 and feedback path 71 of FIG.

Claims (1)

[Scope of Claims] 1. A plurality of two-level display regions each corresponding to a pixel of an image to be displayed and selectively excited and de-excited; means 40 for accessing the display system, each of the display areas having a high threshold level, a low threshold level and a nominal threshold level associated with the area; the threshold level of is intermediate between the high threshold level and the low threshold level, and the access means is arranged such that the intensity of the corresponding image pixel is below the high threshold level associated with the region. only each non-excited region that should be excited because it is at a high level and each excited region that should be non-excited because the intensity of its corresponding image pixel is at a level below said low threshold level associated with that region. 1. A display system configured to access only an image pixel and to reduce the likelihood that noise will superimpose the intensity of its corresponding image pixel to excite or de-excite said display area. 2. In the display system according to claim 1, the display area is configured in a matrix shape consisting of a conceptual plurality of sub-matrices of n area x n area, and the display area in each sub-matrix is A display system characterized in that the regions are associated with different nominal threshold levels derived from a nominal threshold matrix D _o common to the sub-matrices. 3. In the display system according to claim 2, n is a number that is an integer power of 2, and the matrix D _o is a 2×2 array, and the matrix k [4D _o/2 ], k [4D _o/2 +U _o/2 〕k
Consists of [4D _o/2 +2U _o/2 ] and k [4D _o/2 +3U _o/2 ], where D ₂ is the number “0”, “1”, “2” and “3”
It is a 2 × 2 matrix consisting of U _o/2 is an _o/2 × _o/2 matrix in which all elements are “1”,
and k are predetermined scalar constants. 4. A display system according to any one of claims 1 to 3, wherein each of the access means 40 corresponds to one of the display areas and whether the area is excited or not. a first memory 50 for storing a plurality of bits indicative of whether the image pixel is being displayed, and responsive to the intensity of each image pixel being at a level above the high threshold level associated with the corresponding display area; means 21 for generating a first signal and generating a second signal in response to the intensity of each image pixel being at a level below said low threshold level associated with the corresponding display area; signal is present and indicates that the bit in the first memory 50 is in the non-excited region, or the second signal is present and the bit in the first memory is in the excited region. means 41 for generating a signal for accessing its corresponding display area only in response to an indication that the display system 5. In the display system according to claim 4, the access means 40
a second memory 16 for storing a signal representative of said nominal threshold level and depending on whether the corresponding bits stored in said first memory indicate a non-excited region or an excited region, respectively. means 31,3 for obtaining said high threshold level or low threshold level from the signal stored in said second memory;
2, 34, wherein the means for generating the first and second signals compares the intensity of each image pixel to a high threshold level or a low threshold level associated with the pixel to determine the pixel intensity, respectively. is at a level higher than or lower than the high threshold level or the low threshold level.
A display system characterized in that it has a comparator 21 which generates a signal. 6. The display system according to claim 1, wherein the difference between the high threshold level and the low threshold level is variable. 7. In the display system according to claim 6, the high threshold level and the low threshold level are adjusted in response to a percentage of accesses to the display area exceeding a predetermined level. Means 7 for increasing the difference between
A display system characterized by producing 0.71.