FR2846837A1 - Data e.g. fixed images, video, sound sample coding process, involves determining basic list of samples that are to be coded and modifying samples in order to arrange them in decreasing amplitude - Google Patents

Abstract

The process involves determining a basic list of samples that are to be coded. The cost of coding the basic list of samples is provided. The list of the samples is modified in order to arrange them in decreasing amplitude. The above steps are reiterated to find a minimal cost of coding. An Independent claim is also included for a processor of a digital image for coding samples for a whole set of data representing physical sizes.

Description

The present invention relates generally to signal coding

  digital and offers for this purpose a device and a method of

coding of a digital signal.

  The purpose of coding is to compress the signal, which makes it possible to transmit, respectively memorize, the digital signal by reducing the transmission time, or the transmission rate, respectively by

  reducing the memory space used.

  The invention relates to the field of compression with loss of digital signals. The digital signals considered here are of any kind, for example still images, video, sound, data

2 0 IT.

  In the following, we consider more particularly the coding and the

decoding of a still image.

  In this context, certain coding modes use an established route among a set of digital samples. For example, the 25 French patent applications Nos 01 06933, 01 12064 and 01 13922 concern

such coding modes.

  In order for the coding to be effective, that is to say that it has a good bit-distortion ratio, it is necessary to determine the path in an appropriate manner. There are techniques for determining a route among a set of samples. These techniques are known as traveling salesperson problem solving techniques. A review of these techniques is for example exposed in the work of Gerhard Reinelt entitled "The traveling salesman, computational solutions for TSP

  applications ", Springer-Verlag, 1994.

  These techniques use evolutionary computation, which provides an optimal solution to the problem but requires a high computation time. The present invention aims to remedy the drawbacks of the prior art, by providing a method and a device for coding digital data according to which a path is determined more quickly.

than according to the prior art.

  To this end, the invention proposes a method of coding digital samples of a set of data representative of physical quantities, the coding including the determination of an amplitude model and of a path among the samples of the set, characterized in that it comprises the steps of: - determination of a number of samples to be coded, - construction of a list comprising the determined number

  of samples, classified by decreasing amplitude.

  The invention makes it possible to more quickly determine the route among the samples than according to the prior art. The degradation of compression performance (throughput and distortion) is low and generally negligible. According to a first preferred embodiment, the method comprises the steps of: - determining an initial list of samples, - calculating a coding cost as a function of the list of samples, - modifying the list of samples, the calculation and modification steps being repeated to find a

minimum coding cost.

  Thus, according to this embodiment, a list of samples is determined. According to a preferred characteristic, the method further comprises the step of coding the data set from the list of samples

  which provides the minimum coding cost.

  The list determined according to the invention is thus used to code the data. According to a preferred characteristic, the initial list of samples

  contains all the samples in the data set.

  According to a preferred characteristic, the modification of the list

  of samples involves removal of the lower amplitude sample.

  Thus, the lists envisaged will have a number of samples

  decreasing as iterations progress.

  According to preferred characteristics which can be combined, the coding cost comprises the bit rate of the coded data and the coding cost comprises the distortion of the coded data. Bit rate and distortion are commonly taken into account when compressing data. Among the lists envisaged, the one with the lowest coding cost is used to code the data. Determining this list is quick, and by

  construction its coding cost is low.

  According to a second embodiment, the invention relates to a method as previously presented, comprising an initialization of an evolutionary algorithm according to which a population of lists of samples is determined, the population comprising a predetermined number of lists, characterized in what the determination of the population comprises the steps of: - determining a first list of samples classified by decreasing amplitude, - modification of the first list by removing a predetermined number of samples of lower amplitude, for forming a second list, the determination and modification steps being repeated by taking the second list of an iteration as the first list for the next iteration, as long as the predetermined number of lists is not reached and the

  second list has a non-zero number of samples.

  According to this embodiment, it is the initialization of the evolutionary calculation which is simplified and made faster to execute. In addition, the 5 lists created according to the invention are generally better than randomly drawn lists, which means that the convergence of evolutionary calculus

is favored.

  According to a preferred characteristic, the population is supplemented by

  lists drawn at random, if the second list formed has a number of samples zero before the predetermined number of lists is reached.

  According to a preferred characteristic, the data set is a

  block of samples formed in a larger data set.

  According to a preferred characteristic, the data is a digital image. Correlatively, the invention relates to a device for coding digital samples of a set of data representative of physical quantities, comprising means for determining an amplitude model and a path among the samples of the set, characterized in that it comprises: - means for determining a number of samples to be coded, - means for constructing a list comprising the number

  determined samples, classified by decreasing amplitude.

  The device according to the invention comprises means for implementing the characteristics previously presented and has

  2 5 advantages similar to those previously presented.

  The invention also relates to a digital device including the device according to the invention or means for implementing the method according to the invention. This digital camera is for example a digital camera, a digital camcorder, a scanner, a printer, a photocopier, a fax machine. The advantages of the device and the device

  digital are identical to those previously exposed.

  A means of storing information, readable by a computer or by a microprocessor, integrated or not in the device, possibly removable,

  stores a program implementing the method according to the invention.

  A computer program readable by a microprocessor and comprising one or more sequence of instructions is capable of implementing the methods according to the invention.

  The characteristics and advantages of the present invention will appear more clearly on reading a preferred embodiment 10 illustrated by the attached drawings, in which: - Figure 1 is an embodiment of a device implementing the invention, - figure 2 represents a coding device according to the invention and a corresponding decoding device, - figure 3 represents a first embodiment of coding method according to the invention, - figure 4 represents a model d amplitude used according to the present invention,

  FIG. 5 represents a second embodiment of the coding method according to the invention.

  According to the embodiment chosen and represented in FIG. 1, a device implementing the invention is for example a microcomputer 10 connected to different peripherals, for example a digital camera 107 (or a scanner, or any means of acquisition or image storage) connected to

  a graphics card and providing information to be processed according to the invention.

  The device 10 includes a communication interface 112 connected to a network 113 capable of transmitting digital data to be processed or, conversely, of transmitting data processed by the device. The device 10 also includes a storage means 108 such as for example a hard disk. It also includes a disc drive 109. This disc 110 can be a floppy disk, a CD-ROM or a DVD-ROM, for example. The disk 110 like the disk 108 can contain data processed according to the invention as well as the program or programs implementing the invention which, once read by the device 10, will be stored in the hard disk 108. According to a variant, the program allowing the device to implement the invention may be stored in read-only memory 102 (called ROM in the drawing). In a second variant, the program can be received to be stored in an identical manner to that described previously via the communication network 113.

  The device 10 is connected to a microphone 111. The data to be processed 10 according to the invention will in this case be an audio signal.

  This same device has a screen 104 making it possible to view the data to be processed or to serve as an interface with the user who can thus configure certain processing modes, using the keyboard 114 or any

other means (mouse for example).

  The central unit 100 (called CPU in the drawing) executes the instructions relating to the implementation of the invention, instructions stored in the read-only memory 102 or in the other storage elements. During power-up, the processing programs stored in a non-volatile memory, for example the ROM 102, are transferred to the random access memory RAM 103 which will then contain the executable code of the invention as well as registers for memorizing the variables necessary for the implementation of the invention. More generally, a means of storing information, readable by a computer or by a microprocessor, integrated or not in the device, possibly removable, memorizes a program putting in

  the process according to the invention.

  Communication bus 101 allows communication between the

  various elements included in the microcomputer 10 or connected to it. The representation of the bus 101 is not limiting and in particular the central unit 100 30 is capable of communicating instructions to any element of the microcomputer 10 directly or through another element of the microcomputer 10.

  Referring to Figure 2, an embodiment of coding device 3 according to the invention is intended to code a digital signal in order to compress it. The coding device is integrated into an apparatus, which is for example a digital camera, a digital camcorder, a scanner, a printer, a photocopier, a fax machine, a

  database management system or even a computer.

  A digital camera 1 acquires a

  digital image IM. The image is transmitted to an encoding device 2, the operation of which will be detailed below using algorithms.

  The coding device comprises a transformation module 21.

  According to the invention, it comprises: - means 22 for determining a number of samples to be coded, - means 23 for constructing a list comprising the number

  determined samples, classified by decreasing amplitude.

  Finally, it includes a coding module 24 proper.

  The coded image can be transmitted by a transmission module 3, the operation of which is conventional, to a decoding device 4. As a variant, the coded image is simply stored to be decoded later. The decoded image IM 'is for example transmitted to a device

display 5.

  FIG. 3 represents a first embodiment of an image coding method according to the invention. This process is implemented in the

  coding device and comprises steps E1 to E1.

  The method generally comprises a transformation of the signal to be coded, then the determination of an amplitude model of the coefficients resulting from the transformation. The locations of these coefficients are then coded

  according to a method which uses a path established among the coefficients.

  Such a coding method is described for example in the application

French Patent No. 01 06933.

  The method is carried out in the form of an algorithm which can be stored in whole or in part in any information storage means 5 capable of cooperating with the microprocessor. This storage means can be read by a computer or by a microprocessor. This storage means is integrated or not to the device, and can be removable. For example, it may include a magnetic tape, a floppy disk or a CD-ROM (disk

compact with frozen memory).

  Step E1 is a linear or non-linear transformation of a

  digital image IM to be processed according to the invention.

  In the preferred embodiment of the invention, the transformation is a discrete cosine transformation (DCT) by blocks, such as that

applied in the JPEG standard.

  Alternatively, another transformation is used, for example a

  transformation into discrete wavelets, as in the JPEG2000 standard.

  The following processing is carried out block by block, since the DCT transformation generates blocks. If the transformation does not generate

  block, the processing is applied globally to the entire image.

  The next step E2 is an initialization to which a

first block.

  The next step E3 is a classification of the coefficients of the block

  current in decreasing amplitude. The result is a list P of coefficients.

  The next step E4 is the determination of an amplitude model. 25 For this, an approximation function of the sequence of classified coefficients is determined. This function is for example a decreasing exponential defined by a set of parameters which are determined by regression. The

  French patent application No. 01 06933 describes this step in detail.

  FIG. 4 represents an example of an amplitude model A. To each integer value k on the abscissa corresponds a value A (k) supplied by the amplitude model. The value A (k) is an approximation of the amplitude of the

  kth coefficient classified in descending order.

  The next step E5 is the determination of the coding cost associated with the list P. The coding cost of a block is the function C = R + XD, in which R represents the transmission rate of the coded form of the block , D represents the distortion generated in the reconstructed block after coding and decoding, compared to the original block and X is an adjustment parameter between

  image compression and distortion generated by coding.

  It should be noted that the distortion is calculated by performing the sum of the quadratic errors between the amplitude of each coefficient of the block and

  the amplitude it will have after decoding.

  The next step E6 is the storage of the list P as the optimal list Pcpt, if the coding cost C calculated in the previous step is less than the coding cost of the optimal list P0pt previously stored. During the first passage through this step, the current list is memorized as

optimal list.

  The next step E7 is a test to determine whether the current list P

has zero length.

  If the answer is negative, this step is followed by step E8 to which the current list P is modified. The last sample is removed from the list, which results in a new list. Step E8 is followed by step

E5 previously described.

  If the response is positive in step E7, this step is followed by step E9 which is the coding of the current block with the list Popt, that is to say with the list which provides the lowest coding cost. This step is also

  detailed in patent application No. 01 06933.

  This step involves coding the locations of the coefficients from the list P0, pt. For this, a path is determined by an initial coefficient 3 o and the list of vectors joining the other coefficients. Each coefficient of the course different from the initial coefficient is represented by a vector describing its location with respect to the previous coefficient in the course. It should be noted that the course does not necessarily go through all the coefficients of the current block. In fact, it is possible to code only part of the coefficients and to set the other coefficients to zero when

subsequent decoding.

  Once the route has been determined, the coordinates of the initial coefficient are coded by binary coding and the vectors are coded by entropy coding. The coded form of a block of the image includes a model

  of amplitude which provides an approximation of the amplitude of the coefficients and a path which provides an ordered sequence of the locations of the coefficients.

  The location of the keme coefficient of this sequence is determined by the path and its amplitude is determined by the ordinate corresponding to the abscissa k

according to the amplitude model.

  The next step E10 is a test to determine whether the current block 15 is the last block of the image to be coded.

  If the answer is negative, this step is followed by step El 1 in which a next block is considered. Step E11 is followed by step E3

previously described.

  If the response is positive in step E10, then the coding of the image 20 is finished.

  FIG. 5 represents a second embodiment of an image coding method according to the invention. This process is implemented in the

  coding device and comprises steps E20 to E28.

  Again, the method generally comprises a transformation of the signal to be coded, then the determination of an amplitude model of the coefficients resulting from the transformation. The locations of these coefficients are then

  coded according to a method which uses an established path among the coefficients.

  Such a coding method is described for example in French patent application No. 01 06933.

  The invention here relates to the initialization of evolutionary calculus, and more particularly to the determination of an initial population of lists of

  coefficients. This population includes a predetermined number of individuals.

  The method is carried out in the form of an algorithm which can be stored in whole or in part in any information storage means capable of cooperating with the microprocessor. This storage means can be read by a computer or by a microprocessor. This storage means is integrated or not to the device, and can be removable. For example, it may include a magnetic tape, a floppy disk or a CD-ROM (compact disk 10 with frozen memory).

  We consider here the coding of a block of the image. The block considered

has L coefficients.

  Step E20 is an initialization to which the number N of coefficients of the list to be constructed is initialized to the value L. The next step E21 is the construction of a list of coefficients which comprises the N largest coefficients of the block, sorted by order

decreasing in amplitude.

  The next step E22 is the addition of the current list P to the population

  initial of the evolutionary algorithm.

  The next step E23 is a test to determine if the population

  initial contains the desired number of individuals, which are lists here.

  If the answer is negative, this step is followed by step E24 which

  is a test to determine if the current list P has zero length.

  If the answer is negative in step E24, this step is followed by step E25 which is a modification of the number N of coefficients of the list. Through

  for example, the number N is reduced by 10% and rounded to the nearest integer.

  Step E25 is followed by step E21 previously described.

  If the answer is positive in step E24, it is no longer possible to construct lists with the coefficients of the block as explained above and this step is followed by step E26 in which the population is

  supplemented with randomly drawn lists.

  The next step E27 is the calculation of a list of coefficients by evolutionary calculation, from the lists constructed by the previous steps as the initial population of lists. This calculation is carried out as in the

  French patent application n001 06933 and will not be described here.

  If the answer is positive in step E23, this means that the number of lists of the initial population has been reached. This step is then followed by

  step E27 previously described.

  Step E27 is followed by step E28 which is the coding of the block

  current from the list obtained in step E27. Again, this coding is carried out as in French patent application n'0106933.

  Of course, the present invention is in no way limited to the embodiments described and shown, but includes, on the contrary,

  any variant within the reach of the skilled person.

Claims (25)

  1. Method for coding digital samples of a set of data representative of physical quantities, the coding including the determination of an amplitude model and of a path among the samples of the set, characterized in that it includes the steps of: - determination (E5, E20, E25) of a number of samples to be coded, construction (E3, E21) of a list comprising the determined number   of samples, classified by decreasing amplitude.   2. Method according to claim 1, characterized in that it comprises the steps of: - determination (E3) of an initial list of samples, calculation (E5) of a coding cost as a function of the list d 'samples, modification (E8) of the sample list, the calculation and modification steps being repeated to find a minimum coding cost.   3. Method according to claim 2, characterized in that it comprises   furthermore the coding step (E10) of the data set from the list of samples which provides the minimum coding cost.   4. Method according to claim 2 or 3, characterized in that the initial list of samples includes all the samples of the data set.   5. Method according to any one of claims 2 to 4,   characterized in that the modification (E9) of the sample list includes the   withdrawal of the lower amplitude sample.   6. Method according to any one of claims 2 to 5,   characterized in that the coding cost (E6) comprises the bit rate of the coded data.   7. Method according to any one of claims 2 to 6, 10 characterized in that the coding cost (E6) comprises the distortion of coded data.   8. The method as claimed in claim 1, comprising an initialization of an evolutionary algorithm according to which a population of lists of samples is determined, the population comprising a predetermined number of lists, characterized in that the determination of the population comprises the steps of : - determination (E21) of a first list of samples classified by decreasing amplitude, - modification (E25) of the first list by withdrawal of a predetermined number of samples of lower amplitude, to form a second list, the determination and modification steps being reiterated by taking the second list of an iteration as the first list for the next iteration, as long as the predetermined number of lists is not reached (E23) and   that the second list has a non-zero number of samples (E24).   9. Method according to claim 8, characterized in that the population is completed (E26) by lists drawn at random, if the second list formed has a number of samples zero before the number   predetermined list is reached.   10. Method according to any one of claims 1 to 9,   characterized in that the data set is a block of samples formed   into a larger dataset.   11. Method according to any one of claims 1 to 10,   characterized in that the data is a digital image.   12. Device for coding digital samples from a set of data representative of physical quantities, comprising means 10 for determining an amplitude model and a path among the samples of the set, characterized in that '' it comprises (2): - means (22) for determining a number of samples to be coded, - means (23) for constructing a list comprising the number   determined samples, classified by decreasing amplitude.   13. Device according to claim 12, characterized in that it comprises: - means for determining an initial list (P) of samples, - means for calculating a coding cost (C) as a function of the list of samples, - means for modifying the list of samples,   the operation of the calculation and modification means being reiterated to find a minimum coding cost.   14. Device according to claim 13, characterized in that it further comprises means for coding the data set from the list of samples which provides the minimum coding cost. 30 15. Device according to claim 13 or 14, characterized in that the means for determining the initial list of samples are adapted to form it so that it includes all the samples of the data set.   16. Device according to any one of claims 13 to 15, 5 characterized in that the means for modifying the list of samples are adapted to withdraw the sample of lower amplitude.   17. Device according to any one of claims 13 to 16,   characterized in that it is adapted to consider a coding cost which comprises the bit rate of the coded data.   18. Device according to any one of claims 13 to 17,   characterized in that it is suitable for considering a coding cost which comprises the distortion of the coded data.   19. Device according to claim 12, comprising means for initializing an evolutionary algorithm according to which a population of sample lists is determined, the population comprising a predetermined number of lists, characterized in that the means for determining the population includes: means for determining a first list of samples classified by decreasing amplitude, means for modifying the first list by removing a predetermined number of samples of lower amplitude, to form a second list , the operation of the determination and modification means being reiterated by taking the second list of an iteration as the first list for the next iteration, as long as the predetermined number of lists is not reached and the second list has a number d 'samples not zero. 30 20. Device according to claim 19, characterized in that it is suitable for supplementing the population with lists drawn at random, if the second list formed has a number of samples zero before the number   predetermined list is reached.   21. Device according to any one of claims 12 to 20, 5 characterized in that it is adapted to code a data set which is a block of samples formed in a larger set of data.   22. Device according to any one of claims 12 to 21,   characterized in that it is suitable for coding data which is a digital 1o image.   23. Coding device according to any one of claims   12 to 22, characterized in that the determination and construction means are incorporated in: - a microprocessor (100), - a read-only memory (102) comprising a program for processing the data, and - a random access memory (103) comprising registers suitable for recording variables modified during the execution of said program. 20 24. Apparatus for processing (10) a digital image, characterized in that it comprises means suitable for implementing the method according to   any one of claims 1 to 11.   25. Apparatus for processing (10) a digital image, characterized   in that it comprises the device according to any one of claims 12 at 23.