Methods for encoding or decoding in a videoconference system to reduce problems associated with noisy image acquisition

• US 20050025369A1
• Filed: 08/01/2003
• Published: 02/03/2005
• Est. Priority Date: 08/01/2003
• Status: Active Grant

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Polycom Incorporated (Plantronics, Inc.)
• Inventors: Horowitz, Michael J., Shah, Mohammad Athar
• Granted Patent: US 7,782,940 B2
• Time in Patent Office: Days
• US Class Current: 382/239
• CPC Class Codes: H04N 19/105 Selection of the reference unit for prediction within a chosen coding or prediction mode, e.g. adaptive choice of position and number of pixels used for prediction
• CPC Class Codes: H04N 19/132 Sampling, masking or truncation of coding units, e.g. adaptive resampling, frame skipping, frame interpolation or high-frequency transform coefficient masking
• CPC Class Codes: H04N 19/134 characterised by the element, parameter or criterion affecting or controlling the adaptive coding
• CPC Class Codes: H04N 19/136 Incoming video signal characteristics or properties
• CPC Class Codes: H04N 19/137 Motion inside a coding unit, e.g. average field, frame or block difference
• 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 19/196 being specially adapted for the computation of encoding parameters, e.g. by averaging previously computed encoding parameters processing of motion vectors H04N19/513
• CPC Class Codes: H04N 19/197 including determination of the initial value of an encoding parameter H04N19/56 takes precedence
• CPC Class Codes: H04N 19/198 including smoothing of a sequence of encoding parameters, e.g. by averaging, by choice of the maximum, minimum or median value
• CPC Class Codes: H04N 19/507 using conditional replenishment
• CPC Class Codes: H04N 19/587 involving temporal sub-sampling or interpolation, e.g. decimation or subsequent interpolation of pictures in a video sequence
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 7/15 Conference systems

Abstract

Disclosed herein in one embodiment is an adaptive coding threshold algorithm for a videoconference system which alleviates problems due to the erroneous recoding of stationary areas of images caused by image noise. The algorithm, which is preferably implementable on a videoconference encoder, assesses the coding parameters for a current macroblock and the coding parameters for that same macroblock the last time it was coded. If for both macroblocks the coding was non-intra, with a [0,0] motion vector, and with a low quantization parameter, a determination is made that the current macroblock depicts a stationary image. Accordingly, the algorithm increases the coding threshold (T₁) for the blocks within that macroblock, so that it becomes more difficult for those particular blocks to be recoded. This renders the block with stationary content less susceptible to erroneous recoding, while preserving system bandwidth and improving image quality. Additionally, related noise assessment techniques can be employed at the encoder or decoder without the adjustment of the coding threshold T₁.

Claims

1. A method implementable on an encoder for adjusting a coding threshold for encoding a region of an image, wherein the coding threshold determines whether the region should be coded, comprising:

encoding, at a first time, a first image representation of the region using first encoding parameters generated by the encoder;

encoding, at a second time later than the first time, a second image representation of the region using second encoding parameters generated by the encoder;

assessing at least the first and second encoding parameters to determine whether the image is likely stationary; and

if the image is likely stationary, adjusting the coding threshold in the encoder for at least a portion of the region.

2. The method of claim 1, wherein the first and second image representations comprise a matrix of quantized discrete cosine transform coefficients.

3. The method of claim 1, wherein the first and second encoding parameters respectively comprise at least first and second motion vectors.

4. The method of claim 3, wherein assessing to determine whether the image is likely stationary comprises determining whether the first and second motion vectors are substantially zero.

5. The method of claim 1, wherein the first and second encoding parameters respectively comprise at least first and second quantization parameters.

6. The method of claim 5, wherein assessing to determine whether the image is likely stationary comprises determining whether the first and second quantization parameters are respectively below first and second quantization parameter thresholds.

7. The method of claim 1, wherein the first and second encoding parameters respectively comprise first and second motion vectors and first and second quantization parameters.

8. The method of claim 7, wherein assessing to determine whether the image is likely stationary comprises:

determining whether the first and second motion vectors are substantially zero; and

determining whether the first and second quantization parameters are respectively below first and second quantization parameter thresholds.

9. The method of claim 1, wherein adjusting the coding threshold comprises adjusting the coding threshold to decrease the likelihood of encoding the region at the second time.

10. The method of claim 1, wherein adjusting the coding threshold comprises increasing the coding threshold.

11. The method of claim 1, further comprising:

encoding, a third time prior to the first time, a third image representation of the region using third encoding parameters generated by the encoder; and

assessing at least the first, second, and third encoding parameters to determine whether the image is likely stationary.

12. The method of claim 1, wherein the first and second encoding parameters respectively comprise whether the first and second image representations of the region are interceded, and wherein assessing the first and second encoding parameters comprises an assessment whether the first and second image representations of the region are intercoded.

13. A method implementable on an encoder for adjusting a coding threshold for encoding a region of an image, wherein the coding threshold determines whether the region should be coded, comprising:

encoding, at a first time, a first image representation of the region using at least a first quantization parameter and a first motion vector generated by the encoder;

encoding, at a second time later than the first time, a second image representation of the region using at least a second quantization parameter and a second motion vector generated by the encoder; and

adjusting the coding threshold in the encoder for at least a portion of the region if the first and second motion vectors are substantially zero and if the first and second quantization parameters are respectively less than first and second quantization parameter thresholds.

14. The method of claim 13, wherein the first and second image representations comprise a matrix of quantized discrete cosine transform coefficients.

15. The method of claim 13, wherein the first and second quantization parameter thresholds are the same.

16. The method of claim 13, wherein adjusting the coding threshold comprises adjusting the coding threshold to decrease the likelihood of encoding the region at the second time.

17. The method of claim 13, wherein adjusting the coding threshold comprises increasing the coding threshold.

18. The method of claim 13, further comprising:

encoding, a third time prior to the first time, a third image representation of the region using at least a third quantization parameter and a third motion vector generated by the encoder; and

adjusting the coding threshold in the encoder for the region if the first, second, and third motion vectors are substantially zero and if the first, second, and third quantization parameters are respectively less than first, second, and third quantization parameter thresholds.

19. The method of claim 18, wherein the first, second, and third quantization parameter thresholds are the same.

20. The method of claim 13, further comprising:

encoding, at the first time, the first image representation of the region using interceding;

encoding, at the second time, the second image representation of the region using intercoding; and

adjusting the coding threshold in the encoder for at least a portion of the region if the first and second image representations are intercoded.

21. A method implementable on a decoder capable of displaying a region of an image on a display, comprising:

receiving from an encoder, at a first time, a first image representation of the region including first encoding parameters generated by the encoder;

receiving from an encoder, at a second time later than the first time, a second image representation of the region including second encoding parameters generated by the encoder;

assessing at the decoder whether the image is likely stationary using at least the first and second encoding parameters; and

if the image is likely stationary, not updating at least a portion of the region on the display.

22. The method of claim 21, wherein the first and second image representations comprise a matrix of quantized discrete cosine transform coefficients.

23. The method of claim 21, wherein the first and second encoding parameters respectively comprise at least first and second motion vectors.

24. The method of claim 23, wherein assessing to determine whether the image is likely stationary comprises determining whether the first and second motion vectors are substantially zero.

25. The method of claim 21, wherein the first and second encoding parameters respectively comprise at least first and second quantization parameters.

26. The method of claim 25, wherein assessing to determine whether the image is likely stationary comprises determining whether the first and second quantization parameters are respectively below first and second quantization parameter thresholds.

27. The method of claim 21, wherein the first and second encoding parameters respectively comprise first and second motion vectors and first and second quantization parameters.

28. The method of claim 27, wherein assessing to determine whether the image is likely stationary comprises:

determining whether the first and second motion vectors are substantially zero; and

determining whether the first and second quantization parameters are respectively below first and second quantization parameter thresholds.

29. The method of claim 21, further comprising:

receiving from the encoder, a third time prior to the first time, a third image representation of the region including third encoding parameters generated by the encoder; and

assessing at least the first, second, and third encoding parameters to determine whether the image is likely stationary.

30. The method of claim 21, wherein the first and second encoding parameters respectively comprise whether the first and second image representations of the region are interceded, and wherein assessing the first and second encoding parameters comprises an assessment whether the first and second image representations of the region are interceded.

31. The method of claim 21, wherein assessing at the decoder whether the image is likely stationary further comprises whether an error metric for the second image representation of the region is below a threshold.

32. A method implementable on an encoder capable of transmitting image information to a decoder, comprising:

encoding, at a first time, a first image representation of a region of the image using first encoding parameters generated by the encoder;

encoding, at a second time later than the first time, a second image representation of the region using second encoding parameters generated by the encoder;

assessing at least the first and second encoding parameters to determine whether the image is likely stationary; and

if the image is likely stationary, sending a no code signal to a decoder for at least a portion of the region.

33. The method of claim 32, wherein the first and second image representations comprise a matrix of quantized discrete cosine transform coefficients.

34. The method of claim 32, wherein the first and second encoding parameters respectively comprise at least first and second motion vectors.

35. The method of claim 34, wherein assessing to determine whether the image is likely stationary comprises determining whether the first and second motion vectors are substantially zero.

36. The method of claim 32, wherein the first and second encoding parameters respectively comprise at least first and second quantization parameters.

37. The method of claim 36, wherein assessing to determine whether the image is likely stationary comprises determining whether the first and second quantization parameters are respectively below first and second quantization parameter thresholds.

38. The method of claim 32, wherein the first and second encoding parameters respectively comprise first and second motion vectors and first and second quantization parameters.

39. The method of claim 38, wherein assessing to determine whether the image is likely stationary comprises:

determining whether the first and second motion vectors are substantially zero; and

determining whether the first and second quantization parameters are respectively below first and second quantization parameter thresholds.

40. The method of claim 32, further comprising:

encoding, a third time prior to the first time, a third image representation of the region using third encoding parameters generated by the encoder; and

assessing at least the first, second, and third encoding parameters to determine whether the image is likely stationary.

41. The method of claim 32, wherein the first and second encoding parameters respectively comprise whether the first and second image representations of the region are intercoded, and wherein assessing the first and second encoding parameters comprises an assessment whether the first and second image representations of the block are interceded.