Quantization adjustment based on texture level

• US 7,995,649 B2
• Filed: 04/07/2006
• Issued: 08/09/2011
• Est. Priority Date: 04/07/2006
• Status: Active Grant

• Current Assignee: Zhigu Holdings Limited
• Original Assignee: Microsoft Corporation
• Inventors: Zuo, Xiping, Lin, Chih-Lung
• Primary Examiner(s): WONG, ALLEN C
• Application Number:
  US11/400,788
• Publication Number:
  US 20070248164A1
• Time in Patent Office: 1,950 Days
• Field of Search: 375/240, 375/240.01, 375/240.02, 375/240.12, 375/240.16, 375/240.03, 382/238, 382/239, 348/143, 345/582
• US Class Current: 375/240.03
• CPC Class Codes: H04N 19/124 Quantisation
• CPC Class Codes: H04N 19/137 Motion inside a coding unit, e.g. average field, frame or block difference
• 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 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/61 in combination with predictive coding

Abstract

A video encoder identifies a current smooth region of a current picture in a sequence and performs temporal analysis by determining whether a corresponding region in at least one previous and/or future picture is smooth. Based at least in part on the temporal analysis, the encoder adjusts quantization in the current smooth region. An encoder determines a differential quantization interval for a sequence, the interval comprising an interval number. The interval constrains the encoder to skip differential quantization for at least the interval number of predicted pictures after a predicted differentially quantized picture. An encoder analyzes texture in a current picture and sets a smoothness threshold. The encoder compares texture data with the smoothness threshold and adjusts differential quantization for at least part of the current picture based on a finding of at least one smooth region in the current picture according to the smoothness threshold.

Claims

1. In a video encoder, a method comprising:

identifying a current smooth region of a current video picture in a video picture sequence, the video picture sequence having a display order in which display of plural previous pictures occurs before display of the current video picture in the display order and display of plural future pictures occurs after the display of the current video picture in the display order;

performing temporal analysis on the current smooth region, wherein the temporal analysis comprises determining whether a corresponding region in at least one of the plural previous and/or future pictures is smooth wherein the temporal analysis attributes greater weight to smoothness in a corresponding region of a future picture that is temporally nearer to the current video picture than to smoothness in a corresponding region of a future picture that is temporally more distant from the current video picture;

based at least in part on the temporal analysis, adjusting quantization in the current smooth region; and

outputting encoded data for the current video picture.

2. The method of claim 1 wherein the adjusting quantization in the current smooth region comprises reducing a quantization step size for the current smooth region.

3. The method of claim 2 wherein the reducing the quantization step size for the current smooth region avoids introduction of a contouring artifact in the current smooth region when the current video picture is reconstructed.

4. The method of claim 1 wherein the temporal analysis is performed on an adjustable number of the plural future pictures, and wherein the adjustable number is one or greater.

5. The method of claim 1 wherein the current smooth region is a gradient slope region.

6. The method of claim 1 wherein the video encoder analyzes a texture map to identify the current smooth region, and wherein the video encoder analyzes mean luminance values in the temporal analysis.

7. One or more computer-readable memory medium having stored thereon computer executable instructions to cause a computer to perform the method of claim 1.

8. In a video encoder, a method comprising:

analyzing texture in a current video picture;

setting a smoothness threshold for the current video picture based at least in part on the analyzed texture in the current video picture;

comparing texture data of the current video picture with the smoothness threshold;

adjusting differential quantization for at least part of the current video picture based on a finding of at least one smooth region in the current video picture according to the smoothness threshold, wherein adjusting the differential quantization includes determining a percentage of flat blocks in the current video picture and comparing the percentage to one or more percentage thresholds; and

outputting encoded data for the current video picture.

9. The method of claim 8 wherein the analyzing texture comprises analyzing a texture map.

10. The method of claim 8 wherein the analyzing texture comprises applying a sliding window to a gradient value histogram of block gradient values.

11. The method of claim 8

wherein the adjusting differential quantization depends on results of the comparing the percentage to the one or more percentage thresholds.

12. The method of claim 8 wherein the adjusting differential quantization comprises:

identifying an isolated flat block in a texture region in the current video picture; and

skipping the differential quantization for the isolated flat block.