Palette-based image compression method, system and data file

• US 20030076993A1
• Filed: 10/11/2002
• Published: 04/24/2003
• Est. Priority Date: 10/19/2001
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Laboratories of America Incorporated (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Li, Xin
• Granted Patent: US 7,162,077 B2
• Time in Patent Office: Days
• US Class Current: 382/166
• CPC Class Codes: G06T 9/005 Statistical coding, e.g. Huffman, run length coding

Abstract

A system, method and resulting data-file structure involving the compression of palette-based color images. Compression is based upon coding for boundaries that exist in the original uncompressed image, where such boundaries effectively define a character of binary color differentiation between next-adjacent color zones, which differentiation can be expressed as N and not N, where N is one of the colors in the color palette of the original image.

Claims

1. A method for compressing palette-based color images comprising

selecting a palette-based color image for compression, and

performing compression by (a) treating the boundaries between adjacent differentiated colors zones as bi-level (binary-differentiated) images, and (b) coding for these boundaries.

2. The method of claim 1 which further includes, before performing compression, determining the pixel frequency of each color in the palette for the image, and from this determination sorting the palette colors into a sequence in accordance with an ordered frequency hierarchy which is based upon unidirectionally (increasing or decreasing) differentiated color frequency, and wherein compression is performed on the basis of said determining and sorting.

3. The method of claim 2, wherein said sorting involves creating a sequence based upon progressively decreasing color frequency.

4. The method of claim 2, wherein said coding for boundaries progresses in a hierarchical sequential order that relates to successive boundaries, each of which lies as a singular zone-divider between two differentiated color zones, in one of which zones all corresponding pixels in the original selected image have the color N, and in the other of which zones all corresponding pixels in the original image have another color which is not N.

5. The method of claim 4, wherein the color N has a pixel frequency f (N), and the not-N other color has a pixel frequency f (not-N) whose value is either the same as, or on one numeric side of, the value of f (N).

6. The method of claim 5, wherein the mentioned one numeric side is the lower-value side.

7. The method of claim 1, wherein binary differentiation between two adjacent color zones is expressed as a boundary between color N and not color N, where N is one of the colors in the image palette.

8. The method of claim 7, wherein a not color N zone may include more than one color in the palette.

9. A system for compressing palette-based color images comprising

color indexing structure operable to establish a sorted sequence which describes a unidirectional (increasing or decreasing) hierarchy of image pixel-color frequencies, and

coding structure operatively associated with said indexing structure, operable, on the basis of such a sorted sequence, to effect compression by coding the boundaries that exist between adjacent color zones which are characterized by a selected character of binary differentiation.

10. The system of claim 9, wherein the selected characterization of binary differentiation between two such adjacent color zones is expressed as a boundary between color N and not color N, where N is one of the colors in the image palette.

11. A compressed, palette-based, color-image data file comprising

a collection of binary-related boundary data which is associated with original-image boundaries that exist between pairs of adjacent, differently colored image zones, and

a structural quality in said data, whereby the adjacent color zones on opposite sides of each boundary are binary-related by the color characteristics N and not N, where N is one of the colors in the color palette of the original image.