Method and apparatus for compression of digitized image data using a dynamic band recompression scheme

• US 5,768,481 A
• Filed: 06/05/1995
• Issued: 06/16/1998
• Est. Priority Date: 06/05/1995
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Apple Computer Incorporated (Apple Inc.)
• Inventors: Chen, Kok S., Chan, Allen M.
• Primary Examiner(s): Coles, Sr., Edward L.
• Assistant Examiner(s): WALLERSON, MARK E
• Application Number:
  US08/463,783
• Time in Patent Office: 1,107 Days
• Field of Search: 358/530, 358/448, 358/453, 358/538, 358/539, 358/426, 358/261.1, 358/462, 358/430, 358/432, 358/433, 358/261.3, 358/443, 358/261.4, 348/397, 348/398, 348/399, 348/400, 348/401, 348/402, 348/390, 348/391, 348/372, 348/420, 348/421, 348/469, 382/232, 382/239, 382/244, 382/243, 382/233, 382/236, 395/102
• US Class Current: 358/1.2
• CPC Class Codes: H04N 1/648 Transmitting or storing the primary (additive or subtractive) colour signals; Compression thereof H04N1/642 - H04N1/646 take precedence
• CPC Class Codes: H04N 11/042 Codec means
• CPC Class Codes: H04N 19/186 the unit being a colour or a chrominance component
• CPC Class Codes: H04N 19/42 characterised by implementation details or hardware specially adapted for video compression or decompression, e.g. dedicated software implementation H04N19/635 takes precedence
• CPC Class Codes: H04N 19/423 characterised by memory arrangements H04N19/433 takes precedence
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/63 using sub-band based transform, e.g. wavelets

Abstract

The present invention is directed to systems and methods for encoding (for example, compressing) image data while at the same time, improving both the compression ratio and the perceptibility of the decoded (for example, decompressed) image using a dynamic band recompression scheme. In accordance with exemplary embodiments, portions of a compressed image are decompressed upon occurrence of a predetermined condition prior to compression of an entire frame of image data, and then recompressed with subsequent portions of the original image. Exemplary embodiments achieve enhanced fidelity in a decompressed image even when the image data is compressed without segregation into its scanned and non-scanned components.

Claims

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

processing a portion of the frame of image data;

encoding image data included in said portion of the frame of image data; and

dynamically decoding portions of said encoded image data, prior to encoding the entire frame of image data, in response to a predetermined condition.

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

dividing said frame of image data into a plurality of bands of image data.

3. A method according to claim 1, wherein said frame of image data includes a plurality of pixels, each of which is represented by a color value.

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

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 value of each pixel in said frame of image data is represented with at least 32-bits in uncompressed form.

7. A method according to claim 3, further including the step of:

dividing said frame of image data into a plurality of bands of image data, wherein each band includes a plurality of partitioned blocks, and each partitioned block includes a predetermined number of pixels from said frame of image data.

8. A method according to claim 7, wherein said partitioned blocks are tiled in non-overlapping fashion.

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

distinguishing partitioned blocks wherein pixels are color variant from partitioned blocks wherein pixels are color invariant, and encoding partitioned blocks which are color variant using a mask having a plurality of bits, each bit corresponding to a pixel location of said partitioned block.

14. A method according to claim 1, wherein said step of dynamically decoding further includes the step of:

iteratively performing said step of dynamic decoding and a recompression of said frame of image data until the entire frame of image data has been processed.

10. A method of compressing a frame of image data, comprising the steps of:

processing a portion of the frame of image data wherein said frame of image data includes a plurality of pixels, each of which is represented by a color value, and wherein said frame of image data is divided into a plurality of bands of image data, each band including a plurality of partitioned blocks, each partitioned block including a predetermined number of pixels from said frame of image data;

encoding image data included in said portion of the frame of image data by encoding at least some of said partitioned blocks with a mask index to a look-up table during compression of said frame of image data, storing a plurality of geometrical patterns in said look-up table which are defined by different color values for pixels included in each partitioned block, and dynamically updating said plurality of geometrical patterns stored in said look-up table; and

dynamically decoding portions of said encoded image data, prior to encoding the entire frame of image data, in response to a predetermined condition.

11. A method according to claim 10, wherein said step of dynamically decoding further includes the step of:

initiating said dynamic decoding when the number of geometrical patterns detected in said frame of image data exceeds a predetermined number.

16. A method according to claim 10, wherein said step of encoding further includes the steps of:

representing each detected color in said frame of image data with a color index value to a color value look-up table during compression of said frame of image data;

storing a plurality of color values in said color value look-up table during said step of encoding, wherein each of said stored color values correspond to one of said detected colors in said frame of image data; and

dynamically updating said plurality of color values stored in said color value look-up table when a number of colors detected in said frame of image data exceeds a predetermined number.

17. A method according to claim 16, wherein said step of dynamically decoding further includes the step of:

iteratively performing said step of dynamic decoding and a recompression of said frame of image data until the entire frame of image data has been processed.

12. A method of compressing a frame of image data, comprising the steps of:

processing a portion of the frame of image data, wherein said frame of image data includes a plurality of pixels, each of which is represented by a color value;

encoding image data included in said portion of the frame of image data by representing each detected color in said frame of image data with a color index value to a color value look-up table during compression of said frame of image data, storing a plurality of color values in said color value look-up table during said step of encoding, wherein each of said stored color values corresponds to one of said detected colors in said frame of image data, and dynamically updating said plurality of color values stored in said color value look-up table when a number of colors detected in said frame of image data exceeds a predetermined number; and

dynamically decoding portions of said encoded image data prior to encoding the entire frame of image data, in response to a predetermined condition.

13. A method according to claim 12, wherein said step of dynamically decoding further includes a step of:

initiating said dynamic decoding when the number of colors detected in said frame of image data exceeds said predetermined number.

15. A method according to claim 12, wherein said step of dynamically decoding further includes the step of:

iteratively performing said step of dynamic decoding and a recompression of said frame of image data until the entire frame of image data has been processed.

18. Apparatus for compressing a frame of image data comprising:

a processor for separating a frame of image data into a plurality of bands;

a band buffer for storing a band of said frame of image data; and

a processor for encoding image data included in said band of image data, and for dynamically decoding said band of encoded image data, prior to encoding the entire frame of image data, in response to a predetermined condition.