IMAGE ENCODING APPARATUS, IMAGE DECODING APPARATUS AND CONTROL METHOD THEREFOR

Abstract

The present invention is able to determine an encoding parameter using a simple method with little processing load or memory cost, and enables encoding of image data with excellent compression performance. To this end, a prediction error generating unit of an encoding apparatus according to the present invention calculates the difference (prediction error) between a pixel of interest and a predicted value. A prediction order conversion unit converts the prediction error to a non-negative integer, and outputs the non-negative integer as a prediction order M(e). A Golomb encoding unit performs encoding in accordance with a k parameter supplied from a k parameter updating unit. The k parameter updating unit updates the k parameter for use in the next updating based on the prediction order M(e) of the pixel of interest and the k parameter supplied to the Golomb encoding unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1 is a block configuration diagram of an image processing apparatus according to a first embodiment.

FIG. 2 shows a table for quantizing the difference between neighboring pixels.

FIG. 3 shows the relative positional relation between a pixel x for encoding and neighboring pixels a, b and c.

FIG. 4 is a flowchart showing the flow of encoding according the first embodiment.

FIG. 5A is a table showing the relation between Golomb encoding parameters k and the code lengths of symbols.

FIG. 5B is a table showing the relation between Golomb encoding parameters k, the code lengths of symbols, and correction values.

FIG. 6 shows an example of k parameter transition in the image processing apparatus according to the first embodiment.

FIG. 7 shows a probability distribution f(n,1) at which the encoding probability is maximized when k=1.

FIGS. 8A and 8B show transition probabilities for the k parameter.

FIG. 9 shows the configuration of a code stream output from the image processing apparatus.

FIG. 10 is a block configuration diagram of an image processing apparatus according to second and third embodiments.

FIG. 11 is a flowchart showing the flow of processing by a k parameter updating unit 1002 in the second embodiment.

FIG. 12 shows the association between index values i and parameters k in the third embodiment.

FIG. 13 is a flowchart showing the flow of processing by a k parameter updating unit 1002 in the third embodiment.

FIG. 14 is a block configuration diagram of an information processing apparatus in the case where the first to third embodiments are realized by software.

FIG. 15 is a block configuration diagram of an image processing apparatus that performs decoding in the first embodiment.

FIG. 16 shows exemplary Golomb encodes.

Claims

1. An image encoding apparatus comprising: input means for inputting a symbol to be encoded;encoding means for encoding the symbol in accordance with an encoding parameter to generate encoded data;judging means for judging whether the symbol exceeds an upper limit of a target range for the encoding parameter, and whether the symbol falls below a lower limit of the target range; andupdating means for updating the encoding parameter according to a result of the judgment.

2. A control method of controlling an image encoding apparatus, comprising: an input step of inputting a symbol to be encoded;an encoding step of encoding the symbol in accordance with an encoding parameter to generate encoded data;a judging step of judging whether the symbol exceeds an upper limit of a target range for the encoding parameter, and whether the symbol falls below a lower limit of the target range; andan updating step of updating the encoding parameter according to a result of the judgment.

3. A computer program stored on a computer readable storage medium, and for causing a computer to function as an image encoding apparatus claimed in claim 1 as a result of the computer reading and executing the stored computer program.

4. A computer readable storage medium storing a computer program as claimed in claim 3.

5. An image decoding apparatus comprising: input means for inputting encoded data;decoding means for decoding the encoded data in accordance with a decoding parameter to generate symbol data;judging means for judging whether the symbol exceeds an upper limit of a target range for the decoding parameter, and whether the symbol falls below a lower limit of the target range; andupdating means for updating the decoding parameter according to a result of the judgment.

6. A control method of controlling an image decoding apparatus, comprising: an input step of inputting encoded data;a decoding step of decoding the encoded data in accordance with a decoding parameter to generate symbol data;a judging step of judging whether the symbol exceeds an upper limit of a target range for the decoding parameter, and whether the symbol falls below a lower limit of the target range; andan updating step of updating the decoding parameter according to a result of the judgment.

7. A computer program stored on a computer readable storage medium, and for causing a computer to function as an image decoding apparatus claimed in claim 5 as a result of the computer reading and executing the stored computer program.

8. A computer readable storage medium storing a computer program as claimed in claim 7.

9. An image encoding apparatus that encodes image data based on a dynamic probability distribution model, comprising: input means for inputting image data in pixel units;symbol generating means for generating a symbol for entropy encoding from pixel data of interest input by the input means;encoding means for encoding the symbol generated by the symbol generating means in accordance with a given encoding parameter to generate encoded data;judging means for judging whether the encoding parameter used when the symbol is encoded by the encoding means is within a possible range of the encoding parameter at which a codeword of the symbol is within a target code length, exceeds an upper limit of the range, or falls below a lower limit of the range; andupdating means for updating the encoding parameter based on a result of the judgment by the judging means.

10. The image encoding apparatus according to claim 9, wherein the encoding means is Golomb encoding means.

11. The image encoding apparatus according to claim 9, wherein said symbol generating means includes: predicted value calculating means for calculating a predicted value for pixel data of interest from at least one of pixels, which had been encoded, neighboring the pixel data of interest;prediction error calculating means for calculating a prediction error, being a difference between the calculated predicted value and the pixel data of interest; andconversion means for converting a plus/minus sign of the calculated prediction error to a distinguishable non-negative integer value,wherein the symbol generating means generates the non-negative integer value converted by the conversion means as the symbol.

12. The image encoding apparatus according to claim 9, wherein if the encoding parameter used when the symbol is encoded by the encoding means is defined as K, and a lower limit and an upper limit of a range of the encoding parameter at which the length of codeword of the symbol is within a target code length are respectively defined as KSmin and KSmax, the updating meansincreases the encoding parameter K if K<KSmin,decreases the encoding parameter K if KSmax<K, andmaintains the value of the encoding parameter K if KSmin≦K≦KSmax.

13. The image encoding apparatus according to claim 9, further comprising: state information calculating means for calculating state information S for a position of a pixel of interest X, based on data of pixels, which had been encoded, neighboring the pixel of interest X; andencoding parameter storage means for storing an encoding parameter array K[ ] of a possible range of the state information S,wherein the encoding means performs the encoding in accordance with an encoding parameter K[S] specified by the state information S of the pixel data of interest, andthe updating means updates the encoding parameter K[S].

14. The image encoding apparatus according to claim 13, wherein if the encoding parameter used when the symbol is encoded by the encoding means is defined as K[S], and a lower limit and an upper limit of a range of the encoding parameter at which the length of codeword of the symbol is within a target code length are respectively defined as KSmin and KSmax, the updating meansincreases the encoding parameter K[S] if K[S]<KSmin,decreases the encoding parameter K[S] by aprobability of less than 1 if KSmax<K[S], and maintains the value of the encoding parameter K[S] if KSmin≦K[S]≦KSmax.

15. The image encoding apparatus according to claim 9, further comprising: state information calculating means for calculating state information S for a position of a pixel of interest X, based on data of pixels, which had been encoded, neighboring the pixel of interest X;index storage means for storing an index array i[ ] of a possible range of the state information S obtained by the state information calculating means, andencoding parameter storage means for storing an encoding parameter array K[i[ ]] of a possible range of the index array i[ ],wherein the encoding means performs the encoding in accordance with an encoding parameter K[i[S]] specified by the state information S of the pixel data of interest, andthe updating means updates the encoding parameter K[i[S]].

16. The image encoding apparatus according to claim 15, wherein if the encoding parameter used when the symbol is encoded by the encoding means is defined as K[i[S]], and a lower limit and an upper limit of a range of the encoding parameter at which the length of codeword of the symbol is within a target code length are respectively defined as KSmin and KSmax, the updating meansincreases the encoding parameter K[i[S]] by a preset correction value a if K[i[S]]≦KSmin,decreases the encoding parameter K[i[S]] by a correction value β that is smaller than the correction value a if KSmax<K[i[S]], andmaintains the value of the encoding parameter K[i[S]] if KSmin≦K[i[S]]≦KSmax.

17. A control method for an image encoding apparatus that encodes image data based on a dynamic probability distribution model, comprising: an input step of inputting image data in pixel units;a symbol generating step of generating a symbol for entropy encoding from pixel data of interest input in the input step;an encoding step of encoding the symbol generated in the symbol generating step in accordance with a given encoding parameter to generate encoded data;a judging step of judging whether the encoding parameter used when the symbol is encoded in the encoding step is within a possible range of the encoding parameter at which a codeword of the symbol is a target code length, exceeds an upper limit of the range, or falls below a lower limit of the range; andupdating the encoding parameter based on a result of the judgment in the judging step.

18. A computer program stored on a computer readable storage medium, and for causing a computer to function as an image encoding apparatus as claimed in claim 9 as a result of the computer reading and executing the stored computer program.

19. A computer readable storage medium storing a computer program as claimed in claim 18.

20. An image decoding apparatus that decodes encoded image data based on a dynamic probability distribution model, comprising: input means for inputting encoded data in pixel units;decoding means for decoding the encoded data input by the input means in accordance with a given decoding parameter to generate a symbol of a pixel of interest;image data restoring means for restoring pixel data of the pixel of interest from the symbol obtained by decoding;judging means for judging whether the decoding parameter used when the symbol is decoded by the decoding means is within a possible range of an encoding parameter at which a codeword of the symbol is within a target code length, exceeds an upper limit of the range, or falls below a lower limit of the range; andupdating means for updating the decoding parameter based on a result of the judgment by the judging means.

21. A control method for an image decoding apparatus that decodes encoded image data based on a dynamic probability distribution model, comprising: an input step of inputting encoded data in pixel units;a decoding step of decoding the encoded data input in the input step in accordance with a given decoding parameter to generate a symbol of a pixel of interest;a restoring step of restoring pixel data of the pixel of interest from the symbol obtained by decoding;a judging step of judging whether the decoding parameter used when the symbol is decoded in the decoding step is within a possible range of an encoding parameter at which a codeword of the symbol is within a target code length, exceeds an upper limit of the range, or falls below a lower limit of the range; andan updating the decoding parameter based on a result of the judgment in the judging step.

22. A computer program stored on a computer readable storage medium, and for causing a computer to function as an image decoding apparatus as claimed in claim 21 as a result of the computer reading and executing the stored computer program.

23. A computer readable storage medium storing a computer program as claimed in claim 22.