Text recognition during video compression

• US 20060274833A1
• Filed: 06/23/2005
• Published: 12/07/2006
• Est. Priority Date: 06/02/2005
• Status: Active Grant

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Drezner, David, Kojokaro, Gideon
• Granted Patent: US 8,064,516 B2
• Time in Patent Office: Days
• US Class Current: 375/240.160
• CPC Class Codes: H04N 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• CPC Class Codes: H04N 19/139 Analysis of motion vectors, e.g. their magnitude, direction, variance or reliability
• 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 19/159 Prediction type, e.g. intra-frame, inter-frame or bidirectional frame prediction
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/61 in combination with predictive coding

Abstract

A method for encoding an image of a video stream divided into macroblocks comprising determining a maximum of variance of luma blocks in a macroblock, determining if the maximum of variance exceeds a predetermined threshold, determining if the motion vectors of the macroblock are in correlation with a reference macroblock, determining if the macroblock is not an edge macroblock and setting a first quantization level for the macroblock if it meets these conditions and setting a second quantization level for the macroblock if it does not meet these conditions, where the second quantization level is greater than the first quantization level.

Claims

1. A method to encode an image divided into macroblocks, each macroblock including a plurality of luma blocks and a plurality of chroma blocks, wherein each luma and chroma block includes an array of pixels, comprising:

a) determining a maximum variance of luma blocks in a macroblock;

b) quantizing said macroblock using a quantization level based on said maximum variance of said luma blocks; and

c) repeating steps a) and b) for each macroblock in said image.

2. The method of claim 1, wherein said quantizing step includes setting a first quantization level for said macroblock if said maximum variance of said luma blocks is greater than a predetermined threshold, otherwise setting a second quantization level for said macroblock wherein said second quantization level is greater than said first quantization level.

3. The method of claim 1, wherein said quantization step includes setting a first quantization level for said macroblock if said maximum variance of luma blocks is greater than a predetermined threshold and if each of a plurality of reference macroblocks have a maximum variance of their respective luma blocks greater than said predetermined threshold, otherwise setting a second quantization level for said macroblock wherein said second quantization level is greater than said first quantization level.

4. The method of claim 1, wherein said quantization step includes setting a first quantization level for said macroblock if each of a plurality of reference macroblocks have a maximum variance of their respective luma blocks greater than said predetermined threshold, otherwise setting a second quantization level for said macroblock wherein said second quantization level is greater than said first quantization level.

5. The method of claim 4, wherein said reference macroblocks are macroblocks prior to said macroblock and a number of reference macroblocks is at least three.

6. The method of claim 1, wherein said quantization step includes setting a first quantization level for said macroblock if said maximum variance of luma blocks is greater than a predetermined threshold and if each of a plurality of reference macroblocks have a maximum variance of their respective luma blocks greater than said predetermined threshold and if said macroblock is not an edge macroblock, otherwise setting a second quantization level for said macroblock wherein said second quantization level is greater than said first quantization level.

7. The method of claim 1, wherein said quantization step includes setting a first quantization level for said macroblock if each of a plurality of reference macroblocks have a maximum variance of their respective luma blocks greater than said predetermined threshold and if said macroblock is not an edge macroblock, otherwise setting a second quantization level for said macroblock wherein said second quantization level is greater than said first quantization level.

8. The method of claim 1, wherein said image is one of an I-picture, P-picture or a B-picture of an mpeg video stream.

9. A method to encode an image divided into macroblocks, each macroblock including a plurality of luma blocks and a plurality of chroma blocks, wherein each luma and chroma block includes an array of pixels, comprising:

a) determining a maximum variance of luma blocks in a macroblock;

b) determining if said macroblock is in correlation with at least one reference macroblock by computing a correlation between motion vectors of said macroblock and motion vectors of said at least one reference macroblock;

c) quantizing said macroblock using a quantization level based on said maximum variance of said luma blocks and said correlation between said macroblock and said at least one reference macroblock; and

d) repeating steps a) through c) for each macroblock in said image.

10. The method of claim 9, wherein a macroblock is in correlation with an reference macroblock if a horizontal motion vector of said macroblock is in correlation up to a predetermined threshold with a horizontal motion vector of said reference macroblock and if a vertical motion vector of said macroblock is zero.

11. The method of claim 9, wherein said quantizing step includes setting a first quantization level for said macroblock if said maximum variance of said luma blocks is greater than a predetermined threshold and said macroblock is in correlation with at least one reference macroblock, otherwise setting a second quantization level for said macroblock wherein said second quantization level is greater than said first quantization level.

12. The method of claim 9, wherein said quantization step includes setting a first quantization level for said macroblock if said maximum variance of said luma blocks is greater than a predetermined threshold and said macroblock is in correlation with at least one reference macroblock and if each of a plurality of reference macroblocks have a maximum variance of their respective luma blocks greater than a predetermined threshold and are in correlation with their at least one respective reference macroblock, otherwise setting a second quantization level for said macroblock wherein said second quantization level is greater than said first quantization level.

13. The method of claim 9, wherein said quantization step includes setting a first quantization level for said macroblock if each of a plurality of reference macroblocks have a maximum variance of their respective luma blocks greater than a predetermined threshold and are in correlation with their at least one respective reference macroblock, otherwise setting a second quantization level for said macroblock wherein said second quantization level is greater than said first quantization level.

14. The method of claim 13, wherein said reference macroblocks are macroblocks prior to said macroblock and a number of reference macroblocks is at least three.

15. The method of claim 9, wherein said quantization step includes setting a first quantization level for said macroblock if said maximum variance of said luma blocks is greater than a predetermined threshold and said macroblock is in correlation with at least one reference macroblock and if each of a plurality of reference macroblocks have a maximum variance of their respective luma blocks greater than a predetermined threshold and are in correlation with their at least one respective reference macroblock and if said macroblock is not an edge macroblock, otherwise setting a second quantization level for said macroblock wherein said second quantization level is greater than said first quantization level.

16. The method of claim 9, wherein said quantization step includes setting a first quantization level for said macroblock if each of a plurality of reference macroblocks have a maximum variance of their respective luma blocks greater than a predetermined threshold and are in correlation with their at least one respective reference macroblock and if said macroblock is not an edge macroblock, otherwise setting a second quantization level for said macroblock wherein said second quantization level is greater than said first quantization level.

17. The method of claim 9, wherein said image is one of a P-picture or a B-picture of an mpeg video stream.

18. A method to encode a video stream that includes images comprising:

a) receiving an image;

b) identifying regions having a specific characteristic in said image;

c) setting a first quantization level for said identified regions;

d) setting a second quantization level for regions not exhibiting said specific characteristic.

19. The method of claim 18, wherein said characteristic is a shape, a color, text or a pattern.

20. The method of claim 18, wherein said image is part of a MPEG video stream.