Compression encoder, compression encoding method and program

• US 7,916,960 B2
• Filed: 09/06/2006
• Issued: 03/29/2011
• Est. Priority Date: 09/06/2005
• Status: Active Grant

• Current Assignee: Megachips Corporation
• Original Assignee: Megachips Corporation
• Inventors: Mizuno, Yusuke
• Primary Examiner(s): Dang; Duy M
• Application Number:
  US11/515,766
• Publication Number:
  US 20070053598A1
• Time in Patent Office: 1,665 Days
• Field of Search: 382232-233, 382/240, 382/251, 382/128
• US Class Current: 382/240
• CPC Class Codes: H04N 19/115 Selection of the code volume for a coding unit prior to coding
• CPC Class Codes: H04N 19/124 Quantisation
• CPC Class Codes: H04N 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• CPC Class Codes: H04N 19/129 Scanning of coding units, e.g. zig-zag scan of transform coefficients or flexible macroblock ordering [FMO]
• CPC Class Codes: H04N 19/13 Adaptive entropy coding, e.g. adaptive variable length coding [AVLC] or context adaptive binary arithmetic coding [CABAC]
• CPC Class Codes: H04N 19/132 Sampling, masking or truncation of coding units, e.g. adaptive resampling, frame skipping, frame interpolation or high-frequency transform coefficient masking
• CPC Class Codes: H04N 19/154 Measured or subjectively estimated visual quality after decoding, e.g. measurement of distortion use of rate-distortion criteria H04N19/147
• CPC Class Codes: H04N 19/17 the unit being an image region, e.g. an object
• CPC Class Codes: H04N 19/18 the unit being a set of transform coefficients
• CPC Class Codes: H04N 19/184 the unit being bits, e.g. of the compressed video stream
• CPC Class Codes: H04N 19/46 Embedding additional information in the video signal during the compression process H04N19/517, H04N19/68, H04N19/70 take precedence
• CPC Class Codes: H04N 19/645 by grouping of coefficients into blocks after the transform
• CPC Class Codes: H04N 19/647 using significance based coding, e.g. Embedded Zerotrees of Wavelets [EZW] or Set Partitioning in Hierarchical Trees [SPIHT]
• CPC Class Codes: H04N 19/91 Entropy coding, e.g. variable length coding [VLC] or arithmetic coding

Abstract

A rate control unit performs data truncation on a code sequence having been sorted and bit shifted as shown in FIG. 10 so that a desired noise reduction effect is achieved. The data truncation occurs in sequence from the rightmost bit. For example, in FIG. 10, data is truncated from data of bit 0 in a subband VHL4 downwardly in sequence through data of bit 0 in a subband YHH5, and so on. If the desired noise reduction effect can be achieved by truncation of up to bit data in the subband YHH1, data in those subbands in a dotted area in FIG. 10 will be truncated. If the desired noise reduction effect cannot be achieved by truncation of up to bit data in the subband YHH1, data will then be truncated from data of bit 0 in a subband VLL4 downwardly in sequence.

Claims

1. A compression encoding method for compression and coding of an image signal, comprising the steps of:

(a) recursively dividing an image signal into high- and low-pass components by wavelet transform and generating and outputting transform coefficients in a plurality of bandpass components;

(b) determining a quantization step size by dividing a quantization parameter which indicates target image quality by a norm of a filter coefficient;

(c) entropy coding said transform coefficients; and

(d) performing, by a rate control processing unit of a data processing apparatus, rate control by sorting coded data obtained in said step (c) in predetermined order of scanning with said quantization step size to generate a code sequence and then by truncating part of said code sequence based on a desired level of noise reduction, so that a total capacity of said coded data in said code sequence meets target image quality.

7. The compression encoding method according to claim 1, wherein

said step (d) includes the step of determining a target to be truncated in said rate control on a bit-place-by-bit-plane basis.

10. The compression encoding method according to claim 1, wherein

said step (d) includes the step of determining a target to be truncated in said rate control on a pass-by-pass basis.

13. The compression encoding method according to claim 1 or 2, wherein

said step (b) includes the step of determining said quantization step size applying weighting in consideration of human visual characteristics by dividing said quantization parameter by a value obtained by multiplying a norm of a filter coefficient by an energy weighting factor which is a predetermined value determined based on the human visual characteristics.

15. The compression encoding method according to claim 1 or 2, wherein

said step (b) includes the step of, when said quantization step size is less than a predetermined value, multiplying said quantization step size by powers of 2 so that said quantization step size is not less than said predetermined value.

17. The compression encoding method according to claim 15, wherein

said step (d) includes the step of, when said quantization step size is a value obtained by multiplication by powers of 2, bit shifting transform coefficients of said coded data which have been quantized with said quantization step size, by the number of bits corresponding to an exponent of said powers of 2.

2. A compression encoding method for compression and coding of an image signal, comprising the steps of:

(a) recursively dividing an image signal into high- and low-pass components by wavelet transform and generating and outputting transform coefficients in a plurality of bandpass components;

(b) determining a quantization step size by dividing a quantization parameter which indicates target image quality by a norm of a filter coefficient;

(c) setting at least one region of interest in said image signal;

(d) quantizing and sorting, by a quantization processing unit of a data processing apparatus, said transform coefficients with said quantization step size and sorting and bit shifting said transform coefficients on the basis of information on setting said at least one region of interest;

(e) entropy coding said transform coefficients obtained in said step (d); and

(f) performing rate control by truncating part of coded data obtained in said step (e) based on a desired level of noise reduction, so that a total capacity of said coded data meets target image quality.

5. The compression encoding method according to claim 2, further comprising the step of:

(g) assigning a priority to each of said plurality of regions of interest, said step (g) being executed between steps (c) and (d), wherein

said step (d) includes the step of bit shifting said transfer coefficients by a predetermined number of bits determined by said priority.

8. The compression encoding method according to claim 2, wherein

said step (f) includes the step of determining a target to be truncated in said rate control on a bit-plane-by-bit-plane basis.

11. The compression encoding method according to claim 2, wherein

said step (1) includes the step of determining a target to be truncated in said rate control on a pass-by-pass basis.

3. A compression encoding method for compression and coding of an image signal, comprising the steps of:

(a) recursively dividing an image signal into high- and low-pass components by wavelet transform and generating and outputting transform coefficients in a plurality of bandpass components;

(b) setting a plurality of regions of interest in said image signal;

(c) quantizing said transform coefficients;

(d) entropy coding said transform coefficients obtained in said step (c); and

(e) performing, by a rate control processing unit of a data processing apparatus, rate control by sorting and bit shifting coded data obtained in said step (d) on the basis of information on setting said at least one region of interest to generate a code sequence and then by truncating part of said code sequence based on a desired level of noise reduction, so that a total capacity of said coded data meets target image quality.

4. The compression encoding method according to claim 3, wherein said step (c) includes the steps of:

(c-1) determining a quantization step size by dividing a quantization parameter which indicates target image quality by a norm of a filter coefficient; and

(c-2) quantizing said transform coefficients with said quantization step size, and

said step (e) includes the step of sorting said coded data with said quantization step size.

6. The compression encoding method according to claim 3 or 4, further comprising the step of:

(f) assigning a priority to each of said plurality of regions of interest, said step (f) being executed between steps (b) and (e), wherein

said step (d) includes the step of bit shifting said transfer coefficients by a predetermined number of bits determined by said priority.

9. The compression encoding method according to claim 3 or 4, wherein

said step (e) includes the step of determining a target to be truncated in said rate control on a bit-plane-by-bit-plane basis.

12. The compression encoding method according to claim 3 or 4, wherein

said step (e) includes the step of determining a target to be truncated in said rate control on a pass-by-pass basis.

14. The compression encoding method according to claim 4, wherein

said step (c-1) includes the step of determining said quantization step size applying weighting in consideration of human visual characteristics by dividing said quantization parameter by a value obtained by multiplying a norm of a filter coefficient by an energy weighting factor which is a predetermined value determined based on the human visual characteristics.

16. The compression encoding method according to claim 4, wherein

said step (c-1) includes the step of when said quantization step size is less than a predetermined value, multiplying said quantization step size by powers of 2 so that said quantization step size is not less than said predetermined value.

18. The compression encoding method according to claim 16, wherein

said step (e) includes the step of, when said quantization step size is a value obtained by multiplication by powers of 2, bit shifting said coded data which has been quantized with said quantization step size, by the number of bits corresponding to an exponent of said powers of 2.