Method of further compressing JPEG image

• US 20070019875A1
• Filed: 07/21/2005
• Published: 01/25/2007
• Est. Priority Date: 07/21/2005
• Status: Abandoned Application

• Current Assignee: Taiwan Imaging Tek Corporation
• Original Assignee: Taiwan Imaging Tek Corporation
• Inventors: Steinbach, Eckebard, Sung, Chih-Ta, Lan, Yin-Chun, Bauermann, Ingo
• Application Number:
  US11/186,002
• Publication Number:
  US 20070019875A1
• Time in Patent Office: Days
• US Class Current: 382/239
• CPC Class Codes: H04N 19/40 using video transcoding, i.e. partial or full decoding of a coded input stream followed by re-encoding of the decoded output stream
• CPC Class Codes: H04N 19/48 using compressed domain processing techniques other than decoding, e.g. modification of transform coefficients, variable length coding [VLC] data or run-length data motion estimation in a transform domain H04N19/547; processing of decoded motion vectors H04N19/513
• CPC Class Codes: H04N 19/50 using predictive coding H04N19/61 takes precedence
• CPC Class Codes: H04N 19/593 involving spatial prediction techniques
• CPC Class Codes: H04N 19/60 using transform coding

Abstract

Recovered 8×8 DCT coefficient arrays of all block of a JPEG image is formed by reversely decompressing the JPEG image till the procedure of dequantization. A method of redundancy removal of inter-block same subband AC coefficient and intra-block adjacent subband DCT coefficients is applied by re-ordering the coefficients by magnitude of the neighboring subband or a weighted sum of those. The differential values of both inter-block and intra-block DCT coefficients are calculated and coded by an entropy coder to further reduce the data rate. A short code is assigned to represent the “end of non-zero” of each re-ordered subband AC coefficients.

Claims

1. A method of further compressing JPEG image, comprising:

recovering at least two blocks of DCT coefficients of JPEG image by procedure of decompression procedure of “

variable length decoding”

, “

run-length unpacking”

, “

zig-zag scanning” and

“

de-quanitzation”

;

removing inter-block or intra-block redundancy of the recovered DCT coefficients of block image; and

variable length encoding of the selected DCT coefficients from inter-block or intra-block of each block of image.

2. The method of claim 1, wherein the recovering procedure includes the variable length decoding, Run-Length unpacking and dequantization to form an array of 8×

8 DCT coefficients.

3. The method of claim 1, wherein the recovered DCT coefficients are saved in a temporary buffer and form 8×

8 DCT coefficient arrays.

4. The method of claim 1, wherein in removing redundancy of the DCT coefficients, differential values of inter-block same subband DCT coefficients are calculated and coded by a VLC coding.

5. The method of claim 1, wherein in removing redundancy of the DCT coefficients, differential values of intra-block adjacent subband DCT coefficients are calculated and coded by a VLC coding.

6. The method of claim 1, wherein the color components, U/V or Cb/Cr follow the same compression procedure of Y in further compressing JPEG image.

7. A method of removing redundancy of DCT coefficients, comprising re-ordering the DCT coefficient of the AC coefficients according to the magnitude of DCT coefficients of the neighboring frequency;

calculating the differential values of inter-block AC coefficients and intra-block AC coefficients;

coding the differential values of inter-block AC coefficients and intra-block AC coefficients by using variable length coding; and

selecting the shorter code of inter-block and intra-block coding to represent the result of the coding.

8. Method of claim 7, wherein re-ordering the AC coefficients, the neighboring frequency is the next lower or the next higher frequency.

9. Method of claim 7, wherein assigning a shorter code to represent “

end of non-zero”

status where the non-zero coefficient starts.

10. Method of claim 7, wherein during VLC coding of the differential values of the inter-block or intra-block DCT coefficients, only the “

Quotient” and

“

Remainder”

are coded with the “

Divider”

implicitly done by prediction.

11. Method of claim 10, wherein the “

Divider”

is calculated by taking average of adjacent weighted differential values of DCT coefficients with closer having heavier weight and farer less weight.

12. Method of claim 7, wherein adaptively applying an arithmetic coding for coding the differential values of the inter-block and intra-block DCT coefficients.

13. An apparatus of further compressing JPEG image, comprising

an decompression engine recovering the JPEG image to dequantization step and forming the 8×

8 DCT coefficient array;

an device re-ordering the DCT coefficient of the AC coefficients according to the magnitude of the neighboring frequency DCT coefficient;

an engine calculating the differential values of inter-block AC coefficients and intra-block AC coefficients and selecting the one with smaller value for VLC coding;

a calculating unit quantizing the differential values of the inter-block and intra-block coefficients; and

a compression unit coding the differential values of inter-block AC coefficients and intra-block AC coefficients by using a variable length code;

14. Apparatus of claim 13, wherein the color components, U/V or Cb/Cr follow the same compression procedure of Y in further compressing JPEG image.

15. Apparatus of claim 13, wherein during quantizing the differential values of inter-block or intra-block DCT coefficients, the quantization step is minimized to avoid degrading the image quality.

16. Apparatus of claim 13, wherein the color components, U/V or Cb/Cr follow the same compression procedure of Y with larger quantization step.

17. The apparatus of claim 13, wherein a certain amount of the re-ordered differences of adjacent pixels are left with no compression operation.