Digital compression method and system with improved coding efficiency

• US 4,974,078 A
• Filed: 11/13/1989
• Issued: 11/27/1990
• Est. Priority Date: 11/13/1989
• Status: Expired due to Term

• Current Assignee: Eastman Kodak Company
• Original Assignee: Eastman Kodak Company
• Inventors: Tsai, Yusheng T.
• Primary Examiner(s): Britton, Howard W.
• Application Number:
  US07/435,653
• Time in Patent Office: 379 Days
• Field of Search: 358/13, 358/44, 358/133, 358/135, 358/136
• US Class Current: 375/240.18
• CPC Class Codes: H04N 11/044 involving transform 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 19/14 Coding unit complexity, e.g. amount of activity or edge presence estimation H04N19/146 takes precedence
• CPC Class Codes: H04N 19/146 Data rate or code amount at the encoder output
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/18 the unit being a set of transform coefficients
• CPC Class Codes: H04N 19/60 using transform coding
• CPC Class Codes: H04N 23/84 for processing colour signals

Abstract

In a method for creating a scan sequence for a single chip color camera an analysis of typical images, captured through a color filter array, is performed to determine an optimal scan sequence for the particular array and/or the typical images. The images, after being digitally captured, are separated into red, green and a blue image databases and the color databases are processed separately. A Discrete Cosine Transform is performed on blocks of the image data and the average RMS values for the coefficients of the images are determined. The RMS values are sorted in descending order to produce a descending scan sequence that optimizes the performance of run length coding schemes. The scan sequence can be stored in a hardware, firmware or software lookup table as a list of block coordinates or indices and used by the camera system to convert two dimensional blocks of coefficients into one dimensional lists of coefficients suitable for run length coding. The block coefficients are used to convert the decoded coefficients into image blocks before presentation on a color CRT of before producing a color print. By incorporating the method into an image capture system an adaptive system which will optimize coding for different image environments and/or different color filter arrays suitable for the different environments is produced.

Claims

1. A method of producing a coefficient scan sequence for transform coefficients of an image to be encoded, said method comprising the steps of:

(a) transforming reference images producing transform coefficients for the images;

(b) determining average coefficients for the images;

(c) ordering the average coefficients in descending order; and

(d) storing the order of the average coefficients as the scan sequence.

2. A method as recited in claim 1, wherein the reference images are captured through a color filter array.

3. A method as recited in claim 1, wherein step (b) comprises:

(b1) determining RMS values of the coefficients for each image; and

(b2) averaging corresponding RMS value coefficients of the images.

4. A method as recited in claim 1, wherein step (b) comprises:

(b1) determining absolute values of the coefficients for each image; and

(b2) averaging corresponding absolute value coefficients of the images.

5. A method as recited in claim 1, wherein the images are separated into color image data files prior to transforming.

6. A method of producing a coefficient scan sequence for transform coefficients of an image to be encoded, said method comprising the steps of:

(a) capturing reference images through a color filter array;

(b) transforming the reference images producing transform coefficients for the images, comprising;

(b1) separating the images into color image data files; and

(b2) performing a two dimensional spatial frequency block transformation on the data files;

(c) determining average coefficients for the images, comprising;

(c1) determining RMS coefficient values for blocks of each image; and

(c2) averaging corresponding RMS value coefficients of the images producing a block of average RMS value coefficients with corresponding block position coordinates;

(d) sorting the average RMS value coefficients in descending order while carrying the block position coordinates producing a list of coordinates; and

(e) storing the list of coordinates as the scan sequence.

7. An image compression system using a color filter array, comprising:

transform means for performing a transformation of an image producing transform coefficients;

coefficient ordering means for ordering the coefficients in dependence upon the color filter array; and

encoding means for encoding the ordered coefficients.

8. A system as recited in claim 7, further comprising:

analysis means for analyzing reference images through the color filter array and producing a coefficient scan sequence for ordering the coefficients in descending order.

9. A system as recited in claim 7, further comprising:

playback means for decoding the ordered coefficients, reordering the decoded coefficients and inverse transforming the reordered coefficients.

10. An image compression system, comprising:

transform means for performing a transformation on an image producing transform coefficients;

coefficient ordering means for ordering the coefficients in dependence upon analysis of a reference image set; and

encoding means for encoding the ordered coefficients.

11. A system as recited in claim 10, further comprising analysis means for analyzing the images of the reference image set and producing a coefficients scan sequence for ordering the coefficient in descending order.

12. A method of compressing an image, comprising the steps of:

(a) producing transform coefficients for the image;

(b) ordering the coefficients responsive to one of a color filter array used to capture the image and an image reference set representative of the image; and

(c) encoding the ordered coefficients.

13. A method as recited in claim 12, wherein step (b) orders the coefficient in descending order.

14. A scan sequence for transforming a two dimensional block of transform coefficients, produced using a camera with a color filter array having a pattern, into a one dimensional list of the transform coefficients, comprising:

scanning the block of coefficients in a descending order responsive to the color filter array pattern.

15. A scan sequence for transforming a two dimensional block of transform coefficients, produced using a single chip camera, into a one dimensional list of the transform coefficients, comprising:

scanning the block of coefficients in a descending order responsive to analysis of typical images captured by the camera.