FR2619461A1 - METHOD AND VIDEO COMPRESSION CIRCUIT FOR BIT CARD DISPLAY - Google Patents

Abstract

The method of the invention reduces the number of bits that must be physically stored to store a video image. The main steps of the algorithm consist in enriching 4 with zeros a bit map of the video image and in encoding 5 the enriched image in sequences of zeros and bytes of data. The zeros enrichment of the video image is carried out by performing an autocorrelation (shift then execution of one or exclusive) for the horizontal and vertical lines. The number of zeros resulting from each correlation is counted until one can determine which of the combinations produces the richest zeros. The zeros-enriched row bitmap is then encoded in sequences of zeros and data bytes. We recognize 1 special cases, such as for example a row consisting only of zeros or a row consisting only of ones, or a coincidence with the row which is just above or with the one which is two rows above, or again the fact that a code is repeated a certain number of times.

Description

The present invention relates to the field of compression algorithms

  video, and more precisely the field of compression algorithms for graphical displays under

Bitmap shape.

  Numerous data compression methods for computer systems, and data compression for video displays or graphic displays in the form of a bitmap are known. However, all these processes suffer from one or more disadvantages. It would be desirable to have a method for storing data in compressed form after it has been received from a graphics display in the form of a bitmap or other similar device. The data should be stored in a manner that allows them to be decoded using a minimum of resources of the decoding process. In addition, data should be stored in a form that is also

as compact as possible.

  The present invention provides a method and circuit for compressing video information from a graphics display in the form of a bitmap or similar apparatus. The method reduces the number of bits that must be physically stored to store a video image. The main steps of the algorithm are to zero-enrich a bitmap of the video image and to encode the enriched image into sequences of zeros and bytes of data. The zeros enhancement of the video image is performed by performing an autocorrelation (shifting and then executing an EXCLUSIVE OR) for the horizontal and vertical lines. The number of zeros resulting from each correlation is counted until we can determine the number of combinations

  which produces the richest zeros.

  The zeros-enriched bit map is then encoded into zeros and bytes of data sequences. We recognize special cases, such as a row consisting only of zeros or a row consisting of only one, and we assign them a special code. In addition, special codes are assigned in the case of zero coincidence with the row which is just above or with that which is two rows above. Special codes are also assigned to indicate that a code is repeated a number of times. We will see others

  Uses of special codes in the detailed description

  which will follow from the present invention.

  The present invention also provides a method for reconstructing compressed data. This method reads encoded data and recreates uncompressed data. Various methods are provided to optimize the speed of this process, including the use of a table

  to decode certain coded data.

  The present invention also relates to a computer system circuit for implementing this method, comprising: first storage means for storing a video image in the form of a bitmap; first comparing means for determining whether one of the conditions of a predetermined set of conditions is verified by a first row of that video image as a bit map; shifter means for shifting said first row of the video image as a bit map; second comparator means, for comparing this first row of the video image as a bit map to a second row of the same bit map video image, said first comparing means, staggering means and second comparator means for obtaining information for encoding said video image as a bit map; and second means of

  storage, for storing encoded video information.

  Other features and benefits of this

  invention will appear on reading the description

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a flowchart describing the steps involved in coding the video data that may be used for the implementation of the present invention. FIG. a display device with a black square in its center which can be compressed by the method of the present invention; - Figure 2B illustrates the display of the black square after a first compression step which can be executed by the method of the FIG. 2C illustrates the display of the black square after a second compression step that can be performed by the method of the present invention; FIG. 3 illustrates an addressable space of operating codes that can be used for the implementation of the present invention; 4A illustrates rows of data which can be compressed by the method of the pre-processing method. FIG. 4B illustrates a step of executing an EXCLUSIVE OR on rows of data that may be executed by the method of the present invention during data compression; FIG. 4C illustrates data rows and their associated compression code which may be used for the implementation of the present invention; FIG. 5 is a flowchart illustrating the preliminary tests to be performed on rows of data during coding which may be executed by the method of the present invention; FIG. 6 is a flowchart illustrating a method for determining the optimal method of zero enrichment that can be implemented by the present invention; FIG. 7 is a flowchart illustrating a method for reconstructing video data from compressed data that can be implemented by the present invention, - Figure 8 is a flowchart illus a method of processing a row start operation code which may be implemented by the present invention; - Fig. 9 is a flowchart illustrating a decoded row decoding process and execution of an EXCLUSIVE OR which may be implemented by the present invention. We will describe a method of compression and

  recontruction of video data. In the description that will

  follow, we have given many special details such as operating codes, special steps, etc. to allow a complete understanding of the present invention. It is obvious, however, that for those skilled in the art the present invention can be implemented without these particular details. Conversely, well-known structures and techniques have not been described in detail to

  not to unnecessarily burden the description of the

present invention.

  The present invention includes a method of compressing video information, information typically from a bit map display or similar device, and a method for reconstructing the compressed video information to allow redisplaying Datas. The present invention is based on the recognition that a typical video image in bit map form mainly comprises either "white areas" or data patterns. A purely random pattern of white and black areas on a video display

  in the form of bitmap is rare.

  Therefore, the present invention takes advantage of these observations by further zeroing a bitmap of a video image by performing autocorrelation of the vertical and horizontal lines. Enrichment in zeros is due to the large amount of "white surfaces" on the screen before the enrichment process, and the patterns that existed in the video image. The present invention attempts several different correlations by counting the number of zeros produced by each correlation, and uses the

  correlation that produces the richest zeros.

  The display enriched with zeros is then coded, and coded repetitive combinations are recognized and then assigned special codes in order to be able to compress again.

plus the data.

  Referring now to FIG. 1, there is shown the method for compressing data used by the preferred embodiment of the present invention. The method first performs several preliminary tests (block 1) on each input row. These tests will be described in more detail in relation to FIG. 5. These tests are used in particular to examine whether a row consists entirely of zeros or whether the row consists of only one, and so on. If any of several preliminary conditions are satisfied (branch 2),

  memorizes a code and receives the following row as input.

  If none of the preliminary conditions are verified (branch 3), several methods are tried in order to enrich the data (block 4) with zeros. This will be described in more detail with reference to FIG. 6. Then, the block enriched in zeros is coded (block). A test is then run to determine if the compressed data uses less space than the uncompressed information. In the negative (branch 7), the uncompressed information (block 9) is stored. In the affirmative (branch 8), the compressed information is memorized (block 10). The following row of data is then submitted to the same process

  the graphic display in the form of a bitmap.

  Figure 2A illustrates an example of data that can be stored using the method of the present invention. It will be apparent to those skilled in the art that the method of the present invention makes it possible to process, with a variable level of efficiency, any data displayed on a graphic display in the form of a bitmap. Figure 2A illustrates a black rectangle 21 displayed on a video display. One of the data compression methods in Fig. 2A is to execute an EXCLUSIVE OR of each row with the row just above it. The result is shown in Figure 2B. Implementing a process that executes an EXCLUSIVE OR on each row of data in the display produces two lines: line 23 and line 24. Line 23 is on the same row as the top row rectangle 21 of Figure 2 A. Line 24 is one row below the side

lower rectangle 21.

  Figure 2C illustrates the result of using a similar process where an EXCLUSIVE OR is performed on both lines 23 and 24 of Figure 2B. In this case, EXCLUSIVE ORs were executed on the vertical lines of the display, with an EXCLUSIVE OR executed between each

  vertical line and the line immediately to the left.

  The result consists of four pixels 26, 27, 28 and 29 which remain black. Two of the pixels, 26 and 29, are the leftmost pixels of rows 23 and 24. The other two pixels, 27 and 28, are located on the vertical line

  adjacent to the far right pixels of lines 23 and 24.

  These FIGS. 2A, 2B and 2C illustrate the method used by the present invention to enrich bit map data in zeros. However, it will be seen that the preferred embodiment uses several variations of this method to optimize both storage and

data recovery.

  The mode. In order to compress the data, a preferred embodiment of the present invention uses a one-byte (eight-bit) code set. These codes are illustrated in more detail in connection with FIG. 3. The codes can be divided into five main types: normal sequences 31, miscellaneous codes 32, repetition codes 33, large data 34 and zeros of FIG. 35. The normal sequence codes 31 use the hexadecimal values 00 to 7F. The format of a normal sequence code, in the preferred embodiment of the present invention, is Odddzzzz, where ddd is a data byte count value that follows this code byte and zzzz is a zero count value. between 0 and 15. For example, a data string consisting of eight zeros followed by two bytes of data, one represented by the hexadecimal value FF, which corresponds to a completely black portion, and the second byte being represented by the value AA or consisting of a gray, can be encoded by the hexadecimal value 28 FF AA. Thus, four bytes of

  data in three bytes of data.

  With the present invention, a number of different codes are used for storing the information about the rows which have fulfilled the preliminary conditions described with reference to FIG. 1 and FIG. 5, and for storing information concerning that of the processes which

  provided the best row of data enriched with zeros.

  The preferred embodiment of the present invention uses for various codes the hexadecimal values 80 to

9F shown below.

Various codes

Code Description

  $ 80 Compression impossible $ 81 Row made entirely of zeros $ 82 Row formed entirely of ones $ 83 Filling data $ 84 Identical filling data $ 85 Plotting a line above $ 86 Plotting two lines above $ 87 Unused $ 88 (dh, dv) = (16, 0) $ 89 (dh, dv) = (0, 0) $ 8A (dh, dv) = (0,1) $ 8B (dh, dv) = (0,2) $ 8C (dh, dv) = (1 , 0) $ 8D (dh, dv) = (1,1) $ 8E (dh, dv) = (2,2) $ 8F (dh, dv) = (8,0) $ 90 to 9F Not used The hex code 80 indicates that the data can not be compressed without using more space than the original data; Uncompressed data follows the code. Hex code 81 indicates that the row was entirely made up of zeros. Hex code 82 indicates that the row was entirely formed of ones. Hex code 83 indicates that the row consisted of bytes of data that were repeated; in this case, the code is followed by a single byte of data indicating the data byte which is repeated. Hex code 84 indicates that this row reproduces the same byte of data as was repeated in the previous row. Hex code 85 indicates that this row is identical to the row just above it. Hex code 86 indicates that this row is identical to the row that is two rows above it. Hex code 87 is not currently used in the preferred embodiment. Hex codes 88 to 8F indicate which of the various horizontal (dh) and vertical (dv) intervals were used to obtain the best zero-enriched row. In the preferred embodiment, hexadecimal codes 90 to 9F do not

are not currently used.

  Each of these various codes 80 to 9F are used only when analyzing a row at the beginning of this row. In this way, these codes are not used when storing data within a row, and they can be used within a row for

further refinements.

  The codes A0 to BF indicate that the preceding operating code of a byte is repeated between zero and thirty-one times. The format of these codes is lOnnnnn2, where nnnnn is a value between 010 and 3110. For example, if the previous operation code was 81 and a repetition code A6 is detected, the result will be the display of six lines

white.

  The codes CO to DF indicate that a chain of bytes of data follows. The format of these codes, in binary value, is lllddddd, where ddddd is an account value, divided by eight, of the data bytes that follow. For example, if a string of sixteen bytes of data is to be represented, a hexadecimal code C2 (16 - 8 = 2) is stored, followed by

sixteen bytes of data.

  The codes EO to FF indicate that there is a string of zeros in the data. the format of this code is lllzzzzz, zzzzz being an account value, divided by 16, zeros. For example, if a string of 160 zeros has been found in a row of data, a hexadecimal value code CA (160 - 16 = 10, or A16) is stored. Figures 4A to 4C illustrate this method of encoding the data. In FIG. 4A, there is shown a set of rows of data that can be compressed by the method of the present invention. The data consists of a row 41 containing only zeros, followed by four rows 42 which correspond to the display of a black rectangle, then another row 43 consisting only of zeros. The first row 41 may be represented by the code 81, corresponding to a row consisting solely of zeros. The row n 2 can be shifted one bit to the right and can be subjected to an EXCLUSIVE OR with itself. This is shown in Figure 4B. Row No. 44 undergoes an EXCLUSIVE OR with a copy of itself shifted one bit to the right (row 45), giving row 46 as a result. This row is optimized for zeros. An operating code 8C is stored, with the preferred embodiment of the present invention, to indicate a horizontal shift interval to the right of a bit and a vertical zero bit interval when executing the EXCLUSIVE OR. Rows 3, 4, and 5 may be represented by the code 85, which indicates that they are replicas of the lines just above them. Row No. 6 may be represented by the code 81 indicating that it consists only of zeros. FIG. 4C illustrates the rows 1 to 6 and the codes

resulting 50.

  Referring to FIG. 5, there is shown a flowchart illustrating the preliminary tests performed, in the preferred embodiment of the present invention, during data compression. We start by testing a row to determine if it consists entirely of blanks or zeros and, if so, we take branch 55 and record the code indicating that it

is entirely white.

  A test is then run to determine whether the row is entirely black or made up of ones, and if so, take branch 56 and record a code indicating that it is entirely black. A test is then run to determine if the row is repeating the same byte of data over the entire length of the row. If this is the case, take branch 57. If we take branch 57, we run a test to see if the row repeats the same byte as the one that was repeated by the previous row and, if this is the case, take the branch 54 and memorize a code indicating that it repeats the same code. If this is not the case, we memorize a code indicating that it repeats a byte, and we

memorize this byte.

  A check is then made to determine if the row coincides with the row just above it and, if so, take the branch 58 and memorize a code indicating that the row is a replica.

  from the row just above her.

  A test is then run to determine if the row coincides with the row which is two rows above it and, if so, take the branch 59 and memorize a code indicating that the row coincides with the

  row that lies two rows above her.

  As described above with respect to FIG. 1, if none of these preliminary conditions are satisfied, a determination is made of which one of several methods of shifting and executing an EXCLUSIVE OR on rows of data will produce a row that is optimized for zeros. Referring now to Figure 6, there is shown a flowchart of a process for determining the optimal method for zero enrichment as used.

  in the preferred embodiment of the present invention.

  This method first of all initializes several variables, in particular the positioning of a variable, called 'best account', to the value of the number of non-zero words in the current row (block 60). Then we determine which of the words are not the same in the current row and the row just above it (block 61). If this count of non-equal words is less than the value 'best count', take branch 62 and store the value '0' as the best horizontal interval, store the value '1' as the best interval vertical and we memorize the value of the account as being 'better account'. In other words, if it is the optimal process the execution of an EXCLUSIVE OR will be done with as input the row immediately preceding the current row and the current row, without shifting the current row to the right. A check is then made to see if the 'best count' value is less than a threshold value, the threshold value being calculated as two, plus the count value divided by eight of the row buffer words. If 'best count' is less than the threshold value, it is assumed that this is the optimal method to zerosize this row of data. If this is not

  the case, we take the branch 75.

  If we take either branch 63 or branch 75, the next step is to determine the value of the count of words that are not the same in the current row and the row that is two rows apart. above her (block 64). If this count is less than the 'best count' value, take branch 65 and store '0' as the best horizontal interval value and '2' as the best vertical interval value. The account value is then stored as 'best account' (block 76). If 'best count' is less than the threshold value, take branch 77 and assume that the optimal process of zero enrichment is that using as input of an EXCLUSIVE OR the current row and the row which is two rows above the current row. If this is not the case, take branch 78. If we take either branch 68 or branch 78, we execute a loop to determine, among several, that of vertical interval combinations. and horizontal interval that will give the best method of enriching zeros. In the preferred embodiment of the present invention, these combinations comprise a horizontal interval equal to 1 with a vertical interval equal to 0, that is, a shift of one bit to the right of the current row and the use of the shifted row and the current row as input values of an EXCLUSIVE OR, a horizontal interval equal to 1 with a vertical interval equal to 1, a horizontal interval equal to 2 with a vertical interval equal to 2, a horizontal interval equal to 8 with a vertical interval equal to 0, and an interval

  horizontal equal to 16 with a vertical interval equal to 0.

  For each of these combinations, a count value of the non-zero words (block 67) is determined. If this count value is less than the 'best count' value (branch 69), this combination is stored as the one corresponding to the best horizontal interval and the best vertical interval. If the account value is not less than the value 'best account' (branching), the next combination (dh, dv) is tried (branch 71). If there is no other combination (dh, dv), it is assumed that the best values of dh and dv that have been stored are the optimal values to enrich this row with zeros. Fig. 7 is a flowchart showing a process used for decoding the compressed video information, which may be used with the method of the present invention. First, we initialize several variables (block 81). This includes initialization to zero of a variable named 'repetition count value'. Then one enters a loop that is executed for each stored code of the video image. The first step is to determine if 'repetition count value' is greater than zero and, if so, take branch 82 and set the operating code to the previous operating code value, that is, that is, the operating code is repeated and the 'repetition count value' (block 84) is decremented. If 'repetition count value' equals zero (branch 83), the following operating code (block 85) is read. A check is then made to determine if this operating code indicates the beginning of a row of data. If this is not the case (branch 86), the row information is decompressed

(block 88).

  If the code indicates that it is the beginning of a row, we take branch 87. We run a test to determine

  if the operative code is a repetition procedure code.

  If this is the case (branch 89), the 'repetition count value' is set to the repetition count value of the repetition operation code, and the following operation code is stored as the code

operative to repeat (block 91).

  If the operating code is not equal to the repetition procedure code, take branch 90 and execute

  processing a row start operation code (block 92).

  The processing of a row start operation code will be explained in more detail with reference to FIGS. 8 and 9. The data is then put into a buffer (block 93). A test is run to determine if there are other operating codes to be processed. If this is the case, take branch 94. In

  if not, take branch 95.

  The processing of a row start operation code, as performed in the preferred embodiment of the present invention, is shown in FIG. 8. The first step of processing a row start operation code is to look for a code that indicates that the data is not compressed. If the data is not compressed (branch 101), the uncompressed data

  are copied into a buffer (block 110).

  If the data is compressed, a test is run to determine if the operation code indicates that the row should be padded with zeros (i.e., a white row). If the row is filled with zeros (branch 102), an operation is performed to fill the row of zeros (block 111). If not, perform a test to determine if the row is to be filled with one (ie if it is a black row). If this is the case, take the branch 103 and fill the row of ones (block 112). If not, a check is made to determine if the code indicates that one byte of data is repeated throughout the row. If this is the case, we take the branch 104, we read the data byte considered and leduuplicate over the entire row (block 113). Then, a test is run to determine if the opcode indicates that the byte repeated along the preceding row should be repeated along that row. If this is the case, take branch 105 and duplicate the byte of data on

the entire row (block 114).

  In the opposite case, a test is made to determine if the current row is a copy of the row which is just above it and, if this is the case, take the branch 106. This is followed by a copy of the row just above (block 115). Finally, a test is made to determine if the code indicates that the row is an exact replica of the row that is two rows above it and, if so, take the branch 107. In this case, In this case, we copy the row that is two rows above the current row (block 116). If all previous tests were negative, a series of tests are performed to determine which horizontal and vertical intervals should be used for this row in the offset process and

  executing the EXCLUSIVE OR (block 117).

  After setting the current values of horizontal interval and vertical interval, the EXCLUSIVE OR shifting and execution process is performed. The first step may consist in determining for the data row the appropriate horizontal interval and shifting to the left, by a number of bytes equal to the value of the interval, a copy of the row. An EXCLUSIVE OR is then executed with the input of the original current data row and the offset copy of this row. Then, tests are made to determine if the resulting row is to be EXCLUSIVE-OR with the row directly above it or with the row

two rows above.

  Referring now to Fig. 9, first, in the preferred embodiment of the present invention, a check is made to see if the horizontal interval of the current row is '1'. If so, take branch 121. In the preferred embodiment of the present invention, a table is used to transform the stored data row into the data row to be displayed. Using the table increases the processing speed of data. The table is constituted

  by the transformed values of each possible coded value.

  For example, in this table, there is a value 110 located at a relative offset of 141. This is because the value 1110 (10112) shifted to the right of a position (01012), used as an input for the executing an EXCLUSIVE OR with the other input which is 1110, gives as result 1410 (10112 E 10102 = 11102). In this way, the coded row will present a value 1410 retransformed in 1110, thanks to this table. The table contains similar transformation values for the other values, located at

  appropriate offset addresses.

  If the horizontal interval is '2', take branch 124 and use a similar table to obtain the transformed codes (block 123). If the horizontal interval is '8', take branch 125, shift the row by eight bytes and submit it to an EXCLUSIVE OR to obtain the original data. Finally, if the horizontal interval is '16', take branch 127, move the row by 16 bytes and submit it to an EXCLUSIVE OR (block 128). After having processed the horizontal intervals, a check is made to determine if the vertical interval is '1'. If this is the case, branch 130 is used. The current row and the string just above it are used as input to execute an EXCLUSIVE OR to obtain the original value. of the current row (block 131). In the opposite case, a check is made to determine if the vertical interval is '2'. If this is the case, we take branch 132 and subject the current row to an EXCLUSIVE OR with the row that is two rows above it, the result being the original value of this row.

row (block 133).

17 2619461

Claims (23)

  A method for compressing information, characterized in that it comprises the following steps: - enriching a bit map of this information in a first-bit state, and - encoding this enriched bitmap,   to compress said information.   The method of claim 1, wherein the step of encoding the enriched bitmap comprises the steps of: determining whether or not a first row of the bitmap fulfills one of the conditions of a set of predetermined conditions, and - if one of these conditions of the predetermined set of conditions is fulfilled, storing a code belonging to   a first predetermined code set.   The method of claim 2, wherein said predetermined set of conditions includes: - whether or not the first row is wholly in said first bit state, - whether or not said first row is entirely in a second state binary state, - the fact that a first group of bits repeats itself or not in said first row, and - the fact that said first row is identical or not   to a second row of the bitmap.   The method of claim 1, wherein the bit map enhancement comprises the steps of: (a) copying a first row of the bit map, (b) shifting that copy of the first row of a predetermined number of bits in a first direction, (c) execution of an EXCLUSIVE OR using as input values said first row of data and said copy of said first row of data, the result thus obtained being a second data row, (d) determining the number of data words of this second row of data that are in said first bit state, (e) if said number of words in said bit state is greater than a first value, storing of this number of words as the first value and storing said predetermined number as a second value, and (f) repeating steps (b) to (e) for each of the   numbers of a first set of predetermined numbers.   The method of claim 4, wherein the bitmap enrichment further comprises the steps of: (a) executing an EXCLUSIVE OR using as input values said first row of data and a third row of data, this third row of data being shifted by a predetermined number of rows from said first row of data, the result so obtained being a fourth row of data, (b) determining the number of data words of that row of data. fourth row of data in said first bit state, (c) if said number of words in said bit state is greater than a third value, storing said number of words as third value and storing said predetermined number as fourth value , and (d) repetition of steps (a) through (c) for each of   numbers of a second set of predetermined numbers.   The method of claim 5, wherein said first set of predetermined numbers comprises the values one, two, eight and sixteen.   The method of claim 6, wherein said second set of predetermined numbers comprises the values zero, one and two.   The process of claim 1, further comprising   a step of decoding said coded information.   9. The method of claim 8, wherein the decoding of said coded information comprises the steps of: (a) reading an operating code, (b) determining, from this operating code, that the operating code whether or not to indicate the beginning of a first row of data, and (c) if this operating code indicates such a beginning of first row of data, execution of this operating code, (d) otherwise, decompression of said first row of data.   The method of claim 9, wherein the processing of the row start operation code comprises the following steps: (a) if the operation code indicates that the data is not compressed, copying uncompressed data, (b) if the operating code indicates that said first row is composed of bits which are all at a first bit state, filling of that first row with bits at that first bit state, (c) if the operating code indicates that said first row is composed bits that are all at a second bit state, filling that first row with bits at that second bit state, (d) if the operating code indicates that the data is repeating a data block, filling said first row with replicas data block, and (e) if the operating code indicates that said first row is the same as a second row offset by a predetermined number of rows per report t in this first row, copy of this second row.   The method of claim 10, wherein the decompression of said data includes the step of using a table having predetermined values permitting to decompress these data.   The method of claim 1, wherein the encoding of the enriched bitmap includes the step of representing said enriched bitmap with codes representing bit sequences at said first bit state and bit sequences. being at a second binary state.   The process of claim 1 wherein said   first binary state is a low state.   14. A method for compressing and redisplaying video information from a bitmap display device, characterized in that it comprises the following steps: - determining that one of the conditions of a first set of predetermined conditions is or not verified by a first row of data, - if one of the conditions of this first set of predetermined conditions is satisfied, storing one of the codes of a first set of codes, - enriching the bit map of said information in a first binary state by shifting and executing an EXCLUSIVE OR, - encoding this bitmap enriched by representing this bit map in the form of sequences of this first bit state and of sequences of a second binary state, and decoding this information by reading a plurality of operating codes and rebuilding the bit map from these operating codes,   so as to compress and redisplay said information.   The method of claim 14, wherein the first set of predetermined conditions includes: - whether all bits of said first row of said information are at said first bit state or not, - all bits of said first row of said information is or is not in said second bit state, - whether or not a first group of bits repeats in that first row, and - whether said first row is identical or not   to a second row of the bitmap.   The method of claim 14, wherein decompressing said data includes the step of using a transformation table having values   predetermined ways to decompress these data.   17. The method of claim 15, wherein the   first binary state is a low state.   18. The method of claim 17, wherein the   second binary state is a high state.   19. A computer system circuit for compressing video information in the form of a bitmap, characterized by: - first storage means, for storing a video image in the form of a bit map, - first comparison means, for determining if one of the conditions of a set of predetermined conditions is verified by a first row of this video image in the form of a bitmap, - shifting means, to shift this first row of the video image as a bitmap. bits, second comparing means, for comparing this first row of the video image in the form of a bitmap to a second row of this same video image in the form of a bitmap, these first comparator means, staggering means and second means. comparators to obtain a 22 2619461   information making it possible to code said video image in the form of a bit map, and - second storage means, for storing a encoded video information.   The circuit of claim 19, wherein said set of predetermined conditions comprises: - whether all the bits of said first row of said video frame are at a first bit state, - the fact that all the bits of said first row of said video information is or is not in a second bit state, - whether or not a first group of bits repeats in said first row of said video information, and - said first row is identical or not to said second row of said video image in the form of bitmap.   21. The circuit of claim 20, wherein the   first binary state is a low state.   22. The circuit of claim 21, wherein the   second binary state is a high state.   23. The circuit of claim 19, wherein said second comparator means allows execution an EXCLUSIVE OR.