Encoding video signals using selective pre-filtering

• US 5,557,330 A
• Filed: 10/31/1994
• Issued: 09/17/1996
• Est. Priority Date: 10/18/1994
• Status: Expired due to Term

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Intel Corporation
• Inventors: Astle, Brian
• Primary Examiner(s): Chin, Tommy P.
• Assistant Examiner(s): Au, A.
• Application Number:
  US08/332,583
• Time in Patent Office: 687 Days
• Field of Search: 348/384, 348/390, 348/394, 348/397, 348/400, 348/401, 348/402, 348/403, 348/409, 348/412, 348/415, 348/429, 348/607, 348/608, 348/620, 348/669, 348/667, 348/610, 348/420
• US Class Current: 348/394.1
• CPC Class Codes: H04N 19/107 between spatial and temporal predictive coding, e.g. picture refresh
• CPC Class Codes: H04N 19/124 Quantisation
• CPC Class Codes: H04N 19/129 Scanning of coding units, e.g. zig-zag scan of transform coefficients or flexible macroblock ordering [FMO]
• CPC Class Codes: H04N 19/13 Adaptive entropy coding, e.g. adaptive variable length coding [AVLC] or context adaptive binary arithmetic coding [CABAC]
• 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 19/14 Coding unit complexity, e.g. amount of activity or edge presence estimation H04N19/146 takes precedence
• CPC Class Codes: H04N 19/146 Data rate or code amount at the encoder output
• CPC Class Codes: H04N 19/149 by estimating the code amount by means of a model, e.g. mathematical model or statistical model
• CPC Class Codes: H04N 19/15 by monitoring actual compressed data size at the memory before deciding storage at the transmission buffer
• CPC Class Codes: H04N 19/172 the region being a picture, frame or field
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/186 the unit being a colour or a chrominance component
• CPC Class Codes: H04N 19/59 involving spatial sub-sampling or interpolation, e.g. alteration of picture size or resolution
• CPC Class Codes: H04N 19/80 Details of filtering operations specially adapted for video compression, e.g. for pixel interpolation H04N19/635, H04N19/86 take precedence
• CPC Class Codes: H04N 19/91 Entropy coding, e.g. variable length coding [VLC] or arithmetic coding

Abstract

Video frames to be encoded are divided into regions, which are then classified into different classes of regions. One or more different filters are then applied to the regions of different classes to generate pre-filtered video frames which are then further encoded to generate an encoded bit stream. In a preferred embodiment, the regions are classified into substantially changed regions and substantially unchanged regions. The pre-filtered video frames are generated by applying a temporal filter to the substantially unchanged regions and by applying a spatial filter to the substantially changed regions.

Claims

1. A computer-implemented process for encoding video signals, comprising the steps of:

(a) providing a current video frame;

(b) classifying one or more regions of the current video frame into two or more classes of regions;

(c) applying a first filter to only regions classified as being in a first class to generate first filtered video signals of a filtered image corresponding to the current video frame; and

(d) generating an encoded bit stream for the current video frame using the first filtered video signals, wherein;

the current video frame comprises three component planes;

a first component plane of the three component planes contains more component values than each of a second component plane and a third component plane of the three component planes;

step (b) comprises the step of identifying one or more substantially unchanged regions of the first component plane and one or more substantially changed regions of the first component plane;

step (c) comprises the steps of;

(1) applying the first filter to the one or more substantially unchanged regions of the first component plane to generate first-filtered first-component signals;

(2) applying the first filter to one or more regions of the second component plane corresponding to the one or more substantially unchanged regions of the first component plane to generate first-filtered second-component signals; and

(3) applying the first filter to one or more regions of the third component plane corresponding to the one or more substantially unchanged regions of the first component plane to generate first-filtered third-component signals; and

step (d) comprises the step of generating the encoded bit stream using the first-filtered first-component, second-component, and third-component signals.

2. The process of claim 1, wherein:

step (c) comprises the further step of applying a second filter to only regions classified as being in a second class to generate second filtered video signals of the filtered image; and

step (d) comprises the step of generating the encoded bit stream using the first filtered video signals and the second filtered video signals.

3. The process of claim 1, wherein:

step (b) comprises the step of identifying one or more substantially unchanged regions of the current video frame and one or more substantially changed regions of the current video frame;

step (c) comprises the step of applying a temporal filter to the one or more substantially unchanged regions to generate temporally filtered video signals of the filtered image; and

step (d) comprises the step of generating the encoded bit stream using the temporally filtered video signals.

4. The process of claim 3, wherein:

step (c) comprises the further step of copying video signals corresponding to the one or more substantially changed regions to generate copied video signals of the filtered image; and

step (d) comprises the step of generating the encoded bit stream using the temporally filtered video signals and the copied video signals.

5. The process of claim 3, wherein:

step (c) comprises the further step of applying a spatial filter to the one or more substantially changed regions to generate spatially filtered video signals of the filtered image; and

step (d) comprises the step of generating the encoded bit stream using the temporally filtered video signals and the spatially filtered video signals.

6. The process of claim 3, wherein:

the current video frame comprises a Y-component plane, a U-component plane, and a V-component plane;

step (b) comprises the step of identifying one or more substantially unchanged regions of the Y-component plane and one or more substantially changed regions of the Y-component plane;

step (c) comprises the steps of;

(1) applying the temporal filter to the one or more substantially unchanged regions of the Y-component plane to generate temporally filtered Y-component signals;

(2) applying the temporal filter to one or more regions of the U-component plane corresponding to the one or more substantially unchanged regions of the Y-component plane to generate temporally filtered U-component signals; and

(3) applying the temporal filter to one or more regions of the V-component plane corresponding to the one or more substantially unchanged regions of the Y-component plane to generate temporally filtered V-component signals; and

step (d) comprises the step of generating the encoded bit stream using the temporally filtered Y-component, U-component, and V-component signals.

7. The process of claim 6, wherein step (c) comprises the further steps of:

(1) applying a spatial filter to the one, or more substantially changed regions of the Y-component plane to generate spatially filtered Y-component signals;

(2) applying the spatial filter to one or more regions of the U-component plane corresponding to the one or more substantially changed regions of the Y-component plane to generate spatially filtered U-component signals; and

(3) applying the spatial filter to one or more regions of the V-component plane corresponding to the one or more substantially changed regions of the Y-component plane to generate spatially filtered V-component signals; and

step (d) comprises the step of generating the encoded bit stream using the temporally filtered Y-component, U-component, and V-component signals and the spatially filtered Y-component, U-component, and V-component signals.

8. The process of claim 1, wherein:

step (b) comprises the step of identifying one or more substantially unchanged regions of the current video frame and one or more substantially changed regions of the current video frame;

step (c) comprises the step of applying a spatial filter to the one or more substantially changed regions to generate spatially filtered video signals of a filtered image corresponding to the current video frame; and

step (d) comprises the step of generating the encoded bit stream using the spatially filtered video signals.

9. The process of claim 1, wherein step (d) comprises the steps of:

(1) generating DCT coefficients for the current video frame by applying a discrete cosine transform to the filtered image;

(2) quantizing the DCT coefficients to generate quantized DCT coefficients for the current video frame;

(3) run-length encoding the quantized DCT coefficients to generate run-length-encoded signals for the current video frame; and

(4) variable-length encoding the run-length-encoded signals to generate the encoded bit stream for the current video frame.

10. The process of claim 1, wherein step (d) comprises the steps of:

(1) generating DCT coefficients for the current video frame by applying a discrete cosine transform to the filtered image;

(2) generating quantized DCT coefficient differences for the current video frame using the DCT coefficients for the current video frame and corresponding DCT coefficients for a previous video frame;

(3) run-length encoding the quantized DCT coefficient differences to generate run-length-encoded signals for the current video frame; and

(4) variable-length encoding the run-length-encoded signals to generate the encoded bit stream for the current video frame.

11. The process of claim 1, further comprising the step of transmitting the encoded bit stream over a POTS telephone network.

12. An apparatus for encoding video signals, comprising:

(a) means for providing a current video frame;

(b) means for classifying one or more regions of the current video frame into two or more classes of regions;

(c) means for applying a first filter to only regions classified as being in a first class to generate first filtered video signals of a filtered image corresponding to the current video frame; and

(d) means for generating an encoded bit stream for the current video frame using the first filtered video signals, wherein;

the current video frame comprises three component planes;

a first component plane of the three component planes contains more component values than each of a second component plane and a third component plane of the three component planes;

means (b) identifies one or more substantially unchanged regions of the first component plane and one or more substantially changed regions of the first component plane;

means (c);

(1) applies the first filter to the one or more substantially unchanged regions of the first component plane to generate first-filtered first-component signals;

(2) applies the first filter to one or more regions of the second component plane corresponding to the one or more substantially unchanged regions of the first component plane to generate first-filtered second-component signals; and

(3) applies the first filter to one or more regions of the third component plane corresponding to the one or more substantially unchanged regions of the first component plane to generate first-filtered third-component signals; and

means (d) generates the encoded bit stream using the first-filtered first-component, second-component, and third-component signals.

13. The apparatus of claim 12, wherein:

means (c) further applies a second filter to only regions classified as being in a second class to generate second filtered video signals of the filtered image; and

means (d) generates the encoded bit stream using the first filtered video signals and the second filtered video signals.

14. The apparatus of claim 12, wherein:

means (b) identifies one or more substantially unchanged regions of the current video frame and one or more substantially changed regions of the current video frame;

means (c) applies a temporal filter to the one or more substantially unchanged regions to generate temporally filtered video signals of the filtered image; and

means (d) generates the encoded bit stream using the temporally filtered video signals.

15. The apparatus of claim 14, wherein:

means (c) copies video signals corresponding to the one or more substantially changed regions to generate copied video signals of the filtered image; and

means (d) generates the encoded bit stream using the temporally filtered video signals and the copied video signals.

16. The apparatus of claim 14, wherein:

means (c) applies a spatial filter to the one or more substantially changed regions to generate spatially filtered video signals of the filtered image; and

means (d) generates the encoded bit stream using the temporally filtered video signals and the spatially filtered video signals.

17. The apparatus of claim 14, wherein:

the current video frame comprises a Y-component plane, a U-component plane, and a V-component plane;

means (b) identifies one or more substantially unchanged regions of the Y-component plane and one or more substantially changed regions of the Y-component plane;

means (c);

(1) applies the temporal filter to the one or more substantially unchanged regions of the Y-component plane to generate temporally filtered Y-component signals;

(2) applies the temporal filter to one or more regions of the U-component plane corresponding to the one or more substantially unchanged regions of the Y-component plane to generate temporally filtered U-component signals; and

(3) applies the temporal filter to one or more regions of the V-component plane corresponding to the one or more substantially unchanged regions of the Y-component plane to generate temporally filtered V-component signals; and

means (d) generates the encoded bit stream using the temporally filtered Y-component, U-component, and V-component signals.

18. The apparatus of claim 17, wherein means (c):

(1) applies a spatial filter to the one or more substantially changed regions of the Y-component plane to generate spatially filtered Y-component signals;

(2) applies the spatial filter to one or more regions of the U-component plane corresponding to the one or more substantially changed regions of the Y-component plane to generate spatially filtered U-component signals; and

(3) applies the spatial filter to one or more regions of the V-component plane corresponding to the one or more substantially changed regions of the Y-component plane to generate spatially filtered V-component signals; and

means (d) generates the encoded bit stream using the temporally filtered Y-component, U-component, and V-component signals and the spatially filtered Y-component, U-component, and V-component signals.

19. The apparatus of claim 18, wherein the apparatus is a microprocessor and the microprocessor is electrically connected to a memory device via a data bus.

20. The apparatus of claim 12, wherein:

means (b) identifies one or more substantially unchanged regions of the current video frame and one or more substantially changed regions of the current video frame;

means (c) applies a spatial filter to the one or more substantially changed regions to generate spatially filtered video signals of a filtered image corresponding to the current video frame; and

means (d) generates the encoded bit stream using the spatially filtered video signals.

21. The apparatus of claim 12, wherein means (d):

(1) generates DCT coefficients for the current video frame by applying a discrete cosine transform to the filtered image;

(2) quantizes the DCT coefficients to generate quantized DCT coefficients for the current video frame;

(3) run-length encodes the quantized DCT coefficients to generate run-length-encoded signals for the current video frame; and

(4) variable-length encodes the run-length-encoded signals to generate the encoded bit stream for the current video frame.

22. The apparatus of claim 12, wherein means (d):

(1) generates DCT coefficients for the current video frame by applying a discrete cosine transform to the filtered image;

(2) generates quantized DCT coefficient differences for the current video frame using the DCT coefficients for the current video frame and corresponding DCT coefficients for a previous video frame;

(3) run-length encodes the quantized DCT coefficient differences to generate run-length-encoded signals for the current video frame; and

(4) variable-length encodes the run-length-encoded signals to generate the encoded bit stream for the current video frame.

23. The apparatus of claim 12, further comprising means for transmitting the encoded bit stream over a POTS telephone network.

24. The apparatus of claim 12, wherein the apparatus is a microprocessor and the microprocessor is electrically connected to a memory device via a data bus.