Encoding video signals using local quantization levels

• US 5,802,213 A
• Filed: 10/18/1994
• Issued: 09/01/1998
• Est. Priority Date: 10/18/1994
• Status: Expired due to Term

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Intel Corporation
• Inventors: Gardos, Thomas
• Primary Examiner(s): Shalwala, Bipin
• Application Number:
  US08/324,923
• Time in Patent Office: 1,414 Days
• Field of Search: 382/232, 382/233, 382/234, 382/235, 382/236, 382/238, 382/239, 382/243, 382/245, 382/246, 382/250, 382/251, 382/252, 382/253, 358/261.2, 358/430, 348/384, 348/405, 348/440
• US Class Current: 382/239
• 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 19/60 using transform coding
• CPC Class Codes: H04N 19/91 Entropy coding, e.g. variable length coding [VLC] or arithmetic coding

Abstract

Video signals are encoded by dividing a current video frame into regions and generating a local complexity measure and a local quantization level for each region, where the local quantization level is selected using the local complexity measure, a previous complexity measure corresponding to a previous video frame, and a previous quantization level corresponding to the previous video frame. The complexity measures are generated using the DCT coefficients for each region. The region is encoded using the local quantization level to generate an encoded bit stream corresponding to the current video frame.

Claims

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

(a) generating a local complexity measure for a region of a current video frame using transform signals corresponding to the region;

(b) selecting a local quantization level for the region using the local complexity measure, a previous complexity measure corresponding to a previous video frame, and a previous quantization level corresponding to the previous video frame; and

(c) encoding the region using the local quantization level to generate an encoded bit stream corresponding to the current video frame.

2. The process of claim 1, wherein the local complexity measure is a function of DCT coefficients corresponding to the region.

3. The process of claim 2, wherein the local complexity measure is a weighted sum of absolute values of the DCT coefficients.

4. The process of claim 1, wherein step (b) comprises the step of generating the local quantization level Q_l using the local complexity measure C_l, the previous complexity measure C_p, and the previous quantization level Q_p using the formula:

##EQU3## where R is a specified constant.

5. The process of claim 1, wherein:

the previous complexity measure is an average complexity measure for the previous video frame; and

the previous quantization level is an average quantization level for the previous video frame.

6. The process of claim 1, wherein:

the previous complexity measure is a local complexity measure for a corresponding region in the previous video frame; and

the previous quantization level is a local quantization level for the corresponding region in the previous video frame.

7. The process of claim 1, wherein:

the local complexity measure is a weighted sum of absolute values of DCT coefficients corresponding to the region;

the previous complexity measure is an average complexity measure for the previous video frame;

the previous quantization level is an average quantization level for the previous video frame; and

step (b) comprises the step of generating the local quantization level Q_l using the local complexity measure C_l, the previous complexity measure C_p, and the previous quantization level Q_p using the formula;

##EQU4## where R is a specified constant.

8. The process of claim 1, wherein step (c) comprises the steps of:

(1) quantizing DCT coefficients corresponding to the region using the local quantization level to generate quantized DCT coefficients for the current video frame;

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

(3) variable-length encoding the run-length-encoded signals to generate the encoded bit stream.

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

(1) generating quantized DCT coefficient differences for the region using the local quantization level, DCT coefficients for the region, and corresponding DCT coefficients for the previous video frame;

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

(3) variable-length encoding the run-length-encoded signals to generate the encoded bit stream.

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

11. An apparatus for encoding video signals, comprising:

(a) means for generating a local complexity measure for a region of a current video frame using transform signals corresponding to the region;

(b) means for selecting a local quantization level for the region using the local complexity measure for the region of the current video frame, a previous complexity measure corresponding to a previous video frame, and a previous quantization level corresponding to the previous video frame; and

(c) means for encoding the region using the local quantization level to generate an encoded bit stream corresponding to the current video frame.

12. The apparatus of claim 11, wherein the local complexity measure is a function of DCT coefficients corresponding to the region.

13. The apparatus of claim 12, wherein the local complexity measure is a weighted sum of absolute values of the DCT coefficients.

14. The apparatus of claim 11, wherein means (b) is adapted to generate the local quantization level Q_l using the local complexity measure C_l, the previous complexity measure C_p, and the previous quantization level Q_p using the formula:

##EQU5## where R is a specified constant.

15. The apparatus of claim 11, wherein:

the previous complexity measure is an average complexity measure for the previous video frame; and

the previous quantization level is an average quantization level for the previous video frame.

16. The apparatus of claim 11, wherein:

the previous complexity measure is a local complexity measure for a corresponding region in the previous video frame; and

the previous quantization level is a local quantization level for the corresponding region in the previous video frame.

17. The apparatus of claim 11, wherein:

the local complexity measure is a weighted sum of absolute values of DCT coefficients corresponding to each region;

the previous complexity measure is an average complexity measure for the previous video frame;

the previous quantization level is an average quantization level for the previous video frame; and

means (b) is adapted to generate the local quantization level Q_l, using the local complexity measure C_l, the previous complexity measure C_p, and the previous quantization level Q_p using the formula. ##EQU6## where R is a specified constant.

18. The apparatus of claim 17, wherein the apparatus is a microprocessor and the microprocessor is electrically connected to a memory device via a data bus.

19. The apparatus of claim 11, 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 11, wherein means (c) is adapted to:

(1) quantize DCT coefficients corresponding to the region using the local quantization level to generate quantized DCT coefficients for the current video frame;

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

(3) variable-length encode the run-length-encoded signals to generate the encoded bit stream.

21. The apparatus of claim 11, wherein means (c) is adapted to:

(1) generate quantized DCT coefficient differences for the region using the local quantization level, DCT coefficients for the region, and corresponding DCT coefficients for the previous video frame;

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

(3) variable-length encode the run-length-encoded signals to generate the encoded bit stream.

22. The apparatus of claim 11, further comprising means for transmitting the encoded bit stream over a POTS telephone network.

23. An apparatus for encoding video signals, comprising:

a complexity generator adapted to generate a local complexity measure for a region of a current video frame using transform signals corresponding to the region;

a quantization controller adapted to select a local quantization level for the region using the local complexity measure, a previous complexity measure corresponding to a previous video frame, and a previous quantization level corresponding to the previous video frame; and

an encoder adapted to encode the region using the local quantization level to generate an encoded bit stream corresponding to the current video frame.