Methods and apparatus for decoding different portions of a video image at different resolutions

• US 6,370,192 B1
• Filed: 11/20/1997
• Issued: 04/09/2002
• Est. Priority Date: 11/20/1997
• Status: Expired due to Fees

• Current Assignee: Hitachi America Limited (Hitachi, Ltd.)
• Original Assignee: Hitachi America Limited (Hitachi, Ltd.)
• Inventors: Henderson, John, Fuhrer, Jack, Pearlstein, Larry
• Primary Examiner(s): KELLEY, CHRISTOPHER S
• Application Number:
  US08/974,906
• Time in Patent Office: 1,601 Days
• Field of Search: 348/575, 348/397, 348/398, 348/845.1, 375/240
• US Class Current: 375/240
• CPC Class Codes: H04N 19/30 using hierarchical techniques, e.g. scalability H04N19/63 takes precedence
• CPC Class Codes: H04N 19/51 Motion estimation or motion compensation

Abstract

Methods and apparatus for improving the quality of images generated by reduced resolution video decoders and new and improved video decoders which produce reduced resolution images are described. Methods and apparatus for identifying conditions within an image which may significantly degrade image quality if particular portions of the image are used by a reduced resolution decoder as reference data are described. In particular, techniques for identifying blocks of pixels, referred to as constant block regions, having approximately the same intensity in terms of luminance values, are discussed. High contrast vertical and/or horizontal edges will cause significant prediction errors in images generated by reduced resolution decoders under certain conditions. Methods for assessing when such conditions exist and a significant prediction error is likely to occur are described. In addition methods and apparatus for minimizing the effect of such prediction errors in downsampling decoders are also described. One specific embodiment is directed to a new video decoder which decodes portions of a single image, e.g., frame, at different resolutions. Areas of the image along high contrast vertical or horizontal edges are decoded at full resolution while other portions of the same image are decoded at reduced resolution.

Claims

1. A method of decoding encoded video images, the method comprising the steps of:

receiving sufficient encoded video data, corresponding to a single image, to generate a decoded representation of at least one image segment, corresponding to said single image, at a first resolution at which said image segment was encoded;

decoding, at different resolutions, received encoded video data representing different non-overlapping portions of said image segment, at least one portion of said image segment being decoded at a second resolution that is lower than a first resolution at which said image segment was encoded, said decoding producing decoded video data; and

storing the decoded video data representing said image segment in a memory device.

2. The method of claim 1, further comprising the step of:

decoding encoded data representing a second image using the stored decoded video data representing the first image as a reference frame for motion compensated prediction purposes.

3. The method of claim 2, further comprising the step of:

examining the generated decoded video data to detect a horizontal or vertical edge which occurs in the same location in multiple images.

4. The method of claim 3, further comprising the step of:

decoding, at a resolution higher than the second resolution, encoded digital data representing a portion of an additional image, the portion of the additional image encompassing data corresponding to the location of at least a portion of a detected horizontal or vertical edge.

5. The method of claim 4, wherein said portion of the additional image is decoded at the first resolution, the method comprising the step of:

decoding encoded digital data representing an additional portion of the additional image at a resolution that is lower than the first resolution in at least one of two axes.

6. The method of claim 4, further comprising the step of:

examining the generated decoded video data to detect the occurrence and location of image regions which are of a consistent luminance intensity and which repeatedly occur in the same location in multiple images.

7. The method of claim 6, further comprising the step of:

decoding, at a lower resolution than the other portions of the additional image, encoded digital data representing a portion of the additional image where an image region having a consistent luminance intensity has been found to occur in multiple images.

8. The method of claim 2, further comprising the step of:

examining the generated decoded video data to detect the occurrence and location of image regions which are of a consistent luminance intensity and which repeatedly occur in the same location in multiple images.

9. The method of claim 8, further comprising the step of:

decoding, at a lower resolution than the other portions of an additional image, encoded digital data representing a portion of the additional image where an image region having a spatially uniform luminance intensity has been found to occur in multiple frames.

10. The method of claim 9, wherein the region having a consistent luminance intensity corresponds to an upper border portion of video images encoded in letterbox format.

11. The method of claim 10, wherein the step of decoding, at a lower resolution than the other portions of an additional image, encoded digital data includes the step of:

performing a downsampling operation on the data representing the image portions being decoded at the lower resolution.

12. A method of decoding encoded video data, comprising the steps of:

performing a decoding operation on encoded data representing a first image to generate a first set of decoded video data;

selectively performing a data reduction operation on the first set of decoded video data to generate a first reduced set of decoded video data which represents different non-overlapping image portions of the first image at different resolutions; and

storing the first reduced set of decoded video data.

13. The method of claim 12, further comprising:

decoding encoded video data representing a second image using the first reduced set of decoded video data as reference data when performing a motion compensated prediction using a motion vector.

14. The method of claim 13, wherein the applied motion vector was encoded for use with full resolution decoded reference data.

15. A method of decoding encoded video data representing a single image having a border, the method comprising the steps of:

receiving sufficient encoded video data representing the image to generate a full resolution decoded image therefrom;

decoding a first portion of the image encompassing pixels adjacent the border at full resolution; and

decoding a second portion which does not overlap the first portion of the image at a reduced resolution, the reduced resolution being less than the full resolution at which the second portion of the image was encoded.

16. The method of claim 15, wherein the second portion of the image does not encompass pixels located immediately adjacent the boarder.

17. The method of claim 15, wherein the step of decoding the second portion of the image includes the step of:

performing a data reduction operation on the data representing the second portion of the image.

18. The method of claim 17, wherein the data reduction operation is a downsampling operation.

19. The method of claim 17, wherein the data reduction operation is a data compression operation.

20. A video decoder for decoding transform coded digital video data, the video decoder comprising:

an inverse transform coding circuit for performing an inverse transform coding operation on the transform coded digital video data;

a controllable data reduction circuit coupled to the inverse transform coding circuit for performing different data reduction operations on data corresponding to different portions of an image; and

a memory coupled to the controllable data reduction circuit for storing data representing different portions of an image at different resolutions.

21. The video decoder of claim 20, further comprising:

a data reduction control module coupled to the controllable data reduction circuit for controlling the data reduction circuit to perform different amounts of data reduction on data corresponding to different portions of an image.

22. The video decoder of claim 21, further comprising:

a horizontal edge detection circuit coupled to the data reduction control module for providing information regarding edges in the decoded video to the data reduction control module.

23. The video decoder of claim 22, further comprising:

a reference frame information memory for storing information about detected edges.

24. The video decoder of claim 23, wherein the controllable data reduction device is a downsampling circuit which can be controlled to downsample different image portions at different rates.

25. The video decoder of claim 23, wherein the controllable data reduction device is a data compression circuit which can be controlled to perform data compression on data corresponding to different non-overlapping poritons of an image at different rates.

26. The video decoder of claim 20, further comprising:

a constant image region detection circuit coupled to the controllable data reduction circuit for generating information regarding image regions which remain consistent throughout a plurality of frames.

27. A method of decoding encoded data representing a single image, the method comprising the steps of:

receiving encoded video data representing said single image in an amount sufficient, if fully decoded, to generate a decoded full resolution representation of the single image;

a decoding received encoded video data representing different non-overlapping portions of the single image at different resolutions, at least one of the different resolutions being lower than the full resolution at which the video data was encoded in at least one of two directions; and

storing decoded video data representing the single image in a memory device.

28. The method of claim 27, wherein the step of decoding encoded video data representing different portions of the single image includes the steps of:

decoding encoded data corresponding to a first portion of the single image without the use of downsampling; and

decoding encoded data corresponding to a second portion of the single image, the decoding encoded data corresponding to a second portion of the single image including a downsampling operation in the vertical direction.

29. A method of decoding intercoded video images, the method comprising the steps of:

decoding, at different resolutions, encoded video data representing different non-overlapping portions of a first image used as a reference image for motion compensated predictions, at least one portion of the first image being decoded at a second resolution that is lower than a first resolution at which said at least one portion of the first image was encoded, said decoding producing decoded video data;

storing the decoded video data representing different portions of said first image at different resolutions in a memory device; and

performing, while decoding a second image, a motion compensated prediction operation using the stored decoded video data as reference data.

30. An apparatus for processing encoded data representing a first image, the first image being encoded at a first resolution, the apparatus comprising:

a full resolution decoder for decoding said encoded data representing the first image to generate a first set of decoded video data representing the image at the first resolution at which the first image was encoded; and

a selective data reduction module for receiving the first set of decoded video data and for performing a data reduction operation on the first set of decoded video data to generate a first reduced set of decoded video data which represents different non-overlapping image portions of the first image at different resolutions, at least one of said different resolutions being a second resolution which is lower than the first resolution at which the first image was encoded.

31. A decoder apparatus comprising:

a module for receiving sufficient encoded video data representing a single encoded image to generate a full resolution decoded image there from, the encoded image including a border; and

a controllable decoder module coupled to said receiving module for decoding a first portion of the encoded image encompassing pixels adjacent the border at full resolution and decoding a second portion of the encoded image which does not overlap the first portion of the encoded image at a reduced resolution, the reduced resolution being less than the full resolution at which the second portion of the image was encoded.

32. An apparatus for decoding encoded video data representing an image, the apparatus comprising:

a module for receiving a set of encoded video data sufficient, if fully decoded, to generate a decoded full resolution representation of the image;

a controllable decoder module for performing decoding operations on said received set of encoded video data; and

a control module for controlling the controllable decoder module to process the set of encoded video data to decode different non-overlapping portions of the image at different resolutions, at least one of the different resolutions being lower than the full resolution at which the image was encoded in at least one of two dimensions.