Apparatus and Method for Compressing Color Index Map

• US 20160234501A1
• Filed: 02/11/2015
• Published: 08/11/2016
• Est. Priority Date: 02/11/2015
• Status: Active Grant

• Current Assignee: Futurewei Technologies Incorporated (Huawei Investment & Holding Co., Ltd.)
• Original Assignee: Futurewei Technologies Incorporated (Huawei Investment & Holding Co., Ltd.)
• Inventors: Minaee, Shervin, Yu, Haoping
• Granted Patent: US 9,729,885 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06F 18/22 Matching criteria, e.g. proximity measures
• CPC Class Codes: H04N 19/103 Selection of coding mode or of prediction mode
• CPC Class Codes: H04N 19/136 Incoming video signal characteristics or properties
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/184 the unit being bits, e.g. of the compressed video stream
• CPC Class Codes: H04N 19/186 the unit being a colour or a chrominance component
• CPC Class Codes: H04N 19/44 Decoders specially adapted therefor, e.g. video decoders which are asymmetric with respect to the encoder
• CPC Class Codes: H04N 19/463 by compressing encoding parameters before transmission
• CPC Class Codes: H04N 19/50 using predictive coding H04N19/61 takes precedence
• CPC Class Codes: H04N 19/593 involving spatial prediction techniques

Abstract

Embodiments are provided for compressing a color index map in video coding applications including screen content images. An embodiment method includes obtaining, at a video codec device, an image block, and generating a color index map comprising a plurality of entries and representing the image block. Each one of the entries is assigned a color index indicating a respective color. The method further includes assigning, in a correct prediction map, a first bit-value for each one of the entries that is predictable by a neighboring entry in the color index map, and a second bit-value for each one of the entries that is unpredictable by any neighboring entry in the color index map. Further, an actual value from the color index map for the each one of the entries that is unpredictable by any neighboring entry is added in a sequence of non-predictable color indices.

Claims

1. A method for image coding, the method comprising:

obtaining, at a video codec device, an image block;

generating a color index map comprising a plurality of entries and representing the image block, wherein each one of the entries is assigned a color index indicating a respective color;

determining whether each one of the entries is predictable by a neighboring entry in the color index map;

assigning, in a correct prediction map, a first bit-value for each one of the entries that is predictable by a neighboring entry in the color index map;

assigning, in the correct prediction map, a second bit-value for each one of the entries that is unpredictable by any neighboring entry in the color index map; and

adding, in a sequence of non-predictable color indices, an actual value from the color index map for each one of the entries that is unpredictable by any neighboring entry.

2. The method of claim 1 further comprising:

coding jointly, at the video codec device, the correct prediction map and the sequence of non-predictable color indices into a sequence of bits; and

sending the sequence of bits to a decoder.

3. The method of claim 2, wherein the sequence of bits includes, after each second bit-value in the sequence of bits, the actual value for the each one of the entries that is unpredictable by any neighboring entry.

4. The method of claim 1 further comprising:

coding separately, at the video codec device, the correct prediction map and the sequence of non-predictable color indices into a respective sequences of bits; and

sending the respective sequences of bits to a decoder.

5. The method of claim 1, wherein the sequence of non-predictable color indices indicates, to a decoder, which entries in the correct prediction map correspond to which of the indices.

6. The method of claim 1 further comprising, before the assigning and determining steps, adding a left column and a top row to the color index map, wherein the left column and the top row comprise a plurality of entries all assigned a most probable color index in the color index map.

7. The method of claim 1, wherein determining whether each one of the entries is predictable by a neighboring entry in the color index map is in accordance with a distance-based prediction in color intensity domain.

8. The method of claim 7 further comprising:

calculating a first intensity variation in a vertical direction between a left neighbor and a top-left neighbor of the each one of the entries;

calculating a second intensity variation in a horizontal direction between a top neighbor and the top-left neighbor of the each one of the entries; and

selecting a smaller intensity variation between the first intensity variation and the second intensity variation.

9. The method of claim 1, wherein determining whether each one of the entries is predictable by a neighboring entry in the color index map is in accordance with a distance-based prediction in color intensity domain.

10. The method of claim 9 further comprising:

calculating a first absolute value difference in a vertical direction between a left neighbor and a top-left neighbor of the each one of the entries;

calculating a second absolute value difference in a horizontal direction between a top neighbor and the top-left neighbor of the each one of the entries; and

selecting a smaller absolute value difference between the first absolute value difference and the second absolute value difference.

11. The method of claim 1, wherein the first bit-value and the second bit-value include zero-bit and one-bit.

12. A method for image coding, the method comprising:

obtaining, at an video codec device, an image block;

selecting a plurality of major colors for the image block;

assigning, for each pixel or group of pixels in the image block, a color index in a color index map, wherein the color index indicates a respective color from the plurality of major colors;

adding a left column and a top row to the color index map, wherein the left column and the top row comprise a plurality of entries all assigned a most probable color index in the color index map;

assigning, in a correct prediction map, a first bit-value for each color index that is predictable by a neighboring color index of a plurality of selected neighbor color indices in the color index map;

assigning, in the correct prediction map, a second bit-value for each color index that is unpredictable by any neighboring color index of the plurality of selected neighbor color indices in the color index map; and

adding, in a sequence of non-predictable color indices, an actual value of each color index that is unpredictable by any neighboring color index of the plurality of selected neighbor color indices in the color index map, wherein the actual value indicates a respective color from the plurality of major colors.

13. The method of claim 12 further comprising:

coding, at the video codec device, the correct prediction map and the sequence of non-predictable color indices into a sequence of bits; and

sending the sequence of bits to a decoder.

14. The method of claim 13, wherein the the correct prediction map and the sequence of non-predictable color indices are coded using context-adaptive binary arithmetic coding (CABAC).

15. The method of claim 12, wherein the sequence of non-predictable color indices includes the actual value of the each color index that is unpredictable by any neighboring color index in a row-by-row or column-by-column order from the color index map.

16. The method of claim 12, wherein the plurality of selected neighbor color indices for each color index in the color index map include a left neighbor color index adjacent to the color index, a top neighbor color index adjacent to the color index, and a top-left neighbor color index adjacent to the left neighbor color index and the top neighbor color index.

17. An apparatus for video coding, the apparatus comprising:

at least one processor; and

a non-transitory computer readable storage medium storing programming for execution by the at least one processor, the programming including instructions to;

obtain an image block;

generate a color index map comprising a plurality of entries and representing the image block, wherein each one of the entries is assigned a color index indicating a respective color;

determine whether each one of the entries is predictable by a neighboring entry in the color index map;

assign, in a correct prediction map, a first bit-value for each one of the entries that is predictable by a neighboring entry in the color index map;

assign, in the correct prediction map, a second bit-value for each one of the entries that is unpredictable by any neighboring entry in the color index map; and

add, in a sequence of non-predictable color indices, an actual value from the color index map for each one of the entries that is unpredictable by any neighboring entry.

18. The apparatus of claim 17, wherein the programming includes further instructions to:

code jointly the correct prediction map and the sequence of non-predictable color indices into a sequence of bits, wherein the sequence of bits includes, after each second bit-value in the sequence of bits, the actual value from the color index map for the each one of the entries that is unpredictable by any neighboring entry; and

send the sequence of bits to a decoder.

19. The apparatus of claim 17, wherein the programming includes further instructions to:

code separately the correct prediction map and the sequence of non-predictable color indices into a respective sequences of bits; and

send the respective sequences of bits to a decoder.

20. The apparatus of claim 17, wherein the sequence of non-predictable color indices includes the actual value of the each color index that is unpredictable by any neighboring color index in a row-by-row or column-by-column order from the color index map.