Method and apparatus for encoding color image data

• US 6,016,360 A
• Filed: 10/15/1997
• Issued: 01/18/2000
• Est. Priority Date: 06/05/1995
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Apple Computer Incorporated (Apple Inc.)
• Inventors: Nguyen, Hungviet H., Moledina, Riaz A.
• Primary Examiner(s): BELLA, MATTHEW C
• Application Number:
  US08/949,693
• Time in Patent Office: 825 Days
• Field of Search: 382/166, 382/232, 382/239, 382/240, 341/51, 341/67, 358/261.2, 358/430, 345/154, 345/155
• US Class Current: 382/166
• CPC Class Codes: G06T 9/00 Image coding bandwidth or redundancy reduction for static pictures H04N1/41; coding or decoding of static colour picture signals H04N1/64; methods or arrangements for coding, decoding, compressing or decompressing digital video signals H04N19/00

Abstract

The present invention is directed to systems and methods for compressing image data while at the same time, improving both the compression ratio and the perceptibility of the decompressed image, even when the image data is compressed without segregation into its scanned and non-scanned components. In accordance with exemplary embodiments, color data is encoded in a manner which optimizes the color fidelity of a decompressed image obtained from the encoded color data. As a result, improved perceptibility of decompressed images is achieved regardless of whether scanned images, non-scanned images or any combination thereof are collectively compressed. Exemplary embodiments achieve such improved perceptibility regardless of whether the images are monochrome (having varying grey scale values) or color. In addition, improved perceptibility is realized in a manner which permits image data including scanned and/or unscanned images to be compressed in real-time.

Claims

1. A method for processing a frame of image data comprising the steps of:

representing a color of each pixel in said frame of image data by at least one color component;

compressing said frame of image data, said step of compressing further including steps of;

(i) prequantizing the at least one color component of the image data by selectively eliminating all but at least one most significant bit of each at least one color component used to represent the color of each pixel in said frame of image data; and

(ii) encoding the remaining bits of the prequantized data to compress the prequantized data;

storing the encoded remaining bits as compressed image data; and

varying the bits which are selectively eliminated from each at least one color component, from one frame of said image data relative to another frame of said image data.

2. A method according to claim 1, further including a step of:

partitioning the frame of image data into partitioned blocks, wherein each partitioned block includes a predetermined number of pixels from said frame of image data.

3. A method according to claim 2, wherein the color of each pixel in said frame of image data is represented using C,M,Y,K color components.

4. A method according to claim 3, wherein each of said C,M,Y,K color components is an 8-bit value.

5. A method according to claim 3, wherein a color of each pixel in said frame of image data is represented as a value having a variable grey scale level.

6. A method according to claim 3, wherein a color of each pixel in said frame of image data is represented with at least 32-bits.

7. A method according to claim 1, wherein said step of prequantizing further includes a step of:

selecting a predetermined combination of bits from the remaining bits of each color component subsequent to selectively eliminating all but the at least one most significant bit for each color component.

8. A method according to claim 7, wherein said step of encoding further includes a step of:

mapping the remaining bits subsequent to said step of prequantizing into an index value having a number of bits less than said remaining bits, said index value representing an address to a color look-up table.

9. A method according to claim 8, wherein said color look-up table includes a plurality of entries corresponding to different colors which are selected independently of colors included in said image data.

10. A method according to claim 9, wherein said step of mapping is performed using an encoding table.

11. A method according to claim 10, further including a step of:

decompressing said compressed image data using the different colors stored in said look-up table.

12. Apparatus for processing a frame of image data comprising:

a processor for partitioning the frame of image data into partitioned blocks, each block including a predetermined number of pixels from the frame of image data;

a processor for a) prequantizing image data by selectively eliminating bits used to represent at least one color component of each pixel in said frame of image data, b) varying the bits which are selectively eliminated from each at least one color component, from one frame of said image data relative to another frame of said image data, and c) encoding the remaining bits of the prequantized data to compress the prequantized data; and

a memory for storing the encoded remaining bits as compressed image data which represents the image.

13. Apparatus according to claim 12, wherein said processor for prequantizing the image data further includes:

a selector for selecting a predetermined combination of bits from among the bits used to represent the at least one color component; and

a look-up table for encoding the predetermined combination of bits of prequantized data as an index value.

14. Apparatus according to claim 13, further including:

a color look-up table for storing a plurality of color values which are independent of colors included in said image data, said color look-up table being addressable by said index value.

15. Apparatus according to claim 14, further including:

a processor for decompressing said compressed image data.

16. Apparatus according to claim 15, wherein said processor for partitioning said image data, said processor for compressing the image data and said processor for decompressing the compressed image data are formed as a single processor.

17. A method for processing a frame of image data comprising the steps of:

partitioning the frame of image data into partitioned blocks, each partitioned block including a predetermined number of pixels from said frame of image data;

prequantizing at least one color component of the image data by selectively eliminating predetermined bits used to represent the at least one color component;

encoding the remaining bits of the prequantized data to reduce the number of colors used to represent the frame of image data;

storing the encoded remaining bits as image data; and

varying the bits which are selectively eliminated from the at least one color component, from one frame of said image data relative to another frame of said image data.

18. A method according to claim 17, wherein said step of prequantizing further includes a step of:

selecting a predetermined combination of bits from the remaining bits of each color component subsequent to selectively eliminating all but the at least one most significant bit for each color component.

19. A method according to claim 18, wherein said step of encoding further includes a step of:

mapping the remaining bits subsequent to said step of prequantizing into an index value having a number of bits less than said remaining bits, said index value representing an address to a color look-up table.