Process, apparatus and system for selecting quantization levels for encoding video signals

• US 5,532,940 A
• Filed: 04/28/1994
• Issued: 07/02/1996
• Est. Priority Date: 11/24/1993
• Status: Expired due to Term

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Intel Corporation
• Inventors: Agarwal, Rohit, Keith, Michael
• Primary Examiner(s): Ramirez, Ellis B.
• Application Number:
  US08/234,978
• Time in Patent Office: 796 Days
• Field of Search: 364/514 R, 364/514 A, 348/390, 348/391, 348/396, 348/394, 348/395, 348/404, 348/409, 348/412, 348/13, 348/15, 348/19, 348/607, 395/162
• US Class Current: 709/204
• 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 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• 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 19/174 the region being a slice, e.g. a line of blocks or a group of blocks
• 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 19/527 Global motion vector estimation
• 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 19/60 using transform coding
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• 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 19/82 involving filtering within a prediction loop
• CPC Class Codes: H04N 19/86 involving reduction of coding artifacts, e.g. of blockiness
• CPC Class Codes: H04N 19/895 : in combination with error concealment
• CPC Class Codes: H04N 19/91 : Entropy coding, e.g. variable length coding [VLC] or arithmetic coding
• CPC Class Codes: H04N 7/15 : Conference systems
• CPC Class Codes: H04N 7/152 : Multipoint control units therefor
• CPC Class Codes: H04N 7/52 : Systems for transmission of a pulse code modulated video signal with one or more other pulse code modulated signals, e.g. an audio signal or a synchronizing signal assembling of a multiplex stream by combining a video stream with other content or additional data, remultiplexing of multiplex streams, insertion of stuffing bits into the multiplex stream, assembling of a packetised elementary stream at server side H04N21/236; disassembling of a multiplex stream, remultiplexing of multiplex streams, extraction or processing of Service Information, disassembling of packetised elementary stream at client side H04N21/434
• CPC Class Codes: H04Q 11/0435 : Details
• CPC Class Codes: H04Q 2213/13034 : A/D conversion, code compression/expansion
• CPC Class Codes: H04Q 2213/13103 : Memory
• CPC Class Codes: H04Q 2213/13106 : Microprocessor, CPU
• CPC Class Codes: H04Q 2213/13152 : Callback
• CPC Class Codes: H04Q 2213/1319 : Amplifier, attenuation circuit, echo suppressor
• CPC Class Codes: H04Q 2213/13209 : ISDN
• CPC Class Codes: H04Q 2213/1324 : Conference call
• CPC Class Codes: H04Q 2213/13299 : Bus
• CPC Class Codes: H04Q 2213/13337 : Picturephone, videotelephony

Abstract

A quantization level is selected for the current video frame in accordance with a plurality of mappings, wherein each mapping correlates an activity measure with a bits per frame measure and each mapping corresponds to a quantization level of a plurality of quantization levels. The current video frame is encoded in accordance with the selected quantization level.

Claims

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

(a) receiving a current video frame;

(b) selecting a quantization level for the current video frame in accordance with a plurality of mappings, wherein each mapping correlates an activity measure with a bits per frame measure and each mapping corresponds to a quantization level of a plurality of quantization levels; and

(c) encoding the current video frame in accordance with the selected quantization level.

2. The process of claim 1, wherein:

step (b) comprises the steps of;

(1) determining an activity measure for the current video frame; and

(2) selecting the quantization level for the current video frame in accordance with the plurality of mappings and the activity measure.

3. The process of claim 1, wherein:

the current video frame is divided into a plurality of regions, each region being designated for intra encoding or for inter encoding;

the plurality of mappings comprises;

a plurality of intra mappings, wherein each intra mapping correlates an intra activity measure with a bits per frame measure and each intra mapping corresponds to an intra quantization level of a plurality of intra quantization levels; and

a plurality of inter mappings, wherein each inter mapping correlates an inter activity measure with a bits per frame measure and each inter mapping corresponds to an inter quantization level of a plurality of inter quantization levels;

step (b) comprises the step of selecting an intra quantization level and an inter quantization level for the current video frame in accordance with the plurality of intra mappings and the plurality of inter mappings; and

step (c) comprises the step of encoding the current video frame in accordance with the selected intra quantization level and the selected inter quantization level.

4. The process of claim 1, wherein step (a) comprises the steps of:

(1) providing one or more test video sequences, each test video sequence comprising one or more test video frames;

(2) encoding each test video frame of each video sequence with intra encoding, for each intra quantization level of a plurality of intra quantization levels;

(3) generating an IntraSAD measure for each intra encoded test video frame;

(4) determining a bits per frame measure for each intra encoded test video frame;

(5) generating an intra mapping between the IntraSAD measures and the bits per frame measures, for each intra quantization level;

(6) encoding each test video frame of each test video sequence with inter encoding, for each inter quantization level of a plurality of inter quantization levels;

(7) generating an InterSAD measure for each inter encoded test video frame;

(8) determining the bits per frame measure for each inter encoded test video frame; and

(9) generating an inter mapping between the InterSAD measures and the bits per frame measures, for each inter quantization level.

5. The process of claim 4, wherein:

step (a) further comprises the steps of;

(10) initializing a target bits per frame parameter; and

(11) receiving the current video frame, wherein the current video frame is divided into a plurality of regions, each region being designated for intra encoding or for inter encoding;

step (b) comprises the steps of;

(1) generating an average IntraSAD measure for the current video frame;

(2) generating an average InterSAD measure for the current video frame;

(3) determining a percentage of intra regions and a percentage of inter regions for the current video frame;

(4) selecting an intra quantization level and an inter quantization level for the current video frame in accordance with the target bits per frame parameter, the plurality of intra mappings, the plurality of inter mappings, the average IntraSAD measure, the average InterSAD measure, the percentage of intra regions, and the percentage of inter regions; and

step (c) comprises the steps of;

(1) encoding the current frame in accordance with the selected intra quantization level and the selected inter quantization level;

(2) determining the bits per frame measure for the encoded current frame;

(3) updating the target bits per frame parameter in accordance with the bits per frame measure for the encoded current frame; and

(4) repeating steps (a)(11), (b)(1) through (b)(4), and (c)(1) through (c)(3) for a next video frame.

6. The process of claim 5, wherein step (a)(10) comprises the step of initializing the target bits per frame parameter in accordance with a specified target bit rate and a specified target frame rate.

7. An apparatus for encoding video signals, comprising:

(a) means for receiving a current video frame;

(b) means for selecting a quantization level for the current video frame in accordance with a plurality of mappings, wherein each mapping correlates an activity measure with a bits per frame measure and each mapping corresponds to a quantization level of a plurality of quantization levels; and

(c) means for encoding the current video frame in accordance with the selected quantization level.

8. The apparatus of claim 7, wherein:

means (b) comprises;

(1) means for determining an activity measure for the current video frame; and

(2) means for selecting the quantization level for the current video frame in accordance with the plurality of mappings and the activity measure.

9. The apparatus of claim 7, wherein:

the current video frame is divided into a plurality of regions, each region being designated for intra encoding or for inter encoding;

the plurality of mappings comprises;

a plurality of intra mappings, wherein each intra mapping correlates an intra activity measure with a bits per frame measure and each intra mapping corresponds to an intra quantization level of a plurality of intra quantization levels; and

a plurality of inter mappings, wherein each inter mapping correlates an inter activity measure with a bits per frame measure and each inter mapping corresponds to an inter quantization level of a plurality of inter quantization levels;

means (b) comprises means for selecting an intra quantization level and an inter quantization level for the current video frame in accordance with the plurality of intra mappings and the plurality of inter mappings; and

means (c) comprises means for encoding the current video frame in accordance with the selected intra quantization level and the selected inter quantization level.

10. The apparatus of claim 7, wherein means (a) comprises:

(1) means for providing one or more test video sequences, each test video sequence comprising one or more test video frames;

(2) means for encoding each test video frame of each video sequence with intra encoding, for each intra quantization level of a plurality of intra quantization levels;

(3) means for generating an IntraSAD measure for each intra encoded test video frame;

(4) means for determining a bits per frame measure for each intra encoded test video frame;

(5) means for generating an intra mapping between the IntraSAD measures and the bits per frame measures, for each intra quantization level;

(6) means for encoding each test video frame of each test video sequence with inter encoding, for each inter quantization level of a plurality of inter quantization levels;

(7) means for generating an InterSAD measure for each inter encoded test video frame;

(8) means for determining the bits per frame measure for each inter encoded test video frame; and

(9) means for generating an inter mapping between the InterSAD measures and the bits per frame measures, for each inter quantization level.

11. The apparatus of claim 10, wherein:

means (a) further comprises;

(10) means for initializing a target bits per frame parameter; and

(11) means for receiving the current video frame, wherein the current video frame is divided into a plurality of regions, each region being designated for intra encoding or for inter encoding;

means (b) comprises;

(1) means for generating an average IntraSAD measure for the current video frame;

(2) means for generating an average InterSAD measure for the current video frame;

(3) means for determining a percentage of intra regions and a percentage of inter regions for the current video frame;

(4) means for selecting an intra quantization level and an inter quantization level for the current video frame in accordance with the target bits per frame parameter, the plurality of intra mappings, the plurality of inter mappings, the average IntraSAD measure, the average InterSAD measure, the percentage of intra regions, and the percentage of inter regions; and

means (c) comprises;

(1) means for encoding the current frame in accordance with the selected intra quantization level and the selected inter quantization level;

(2) means for determining the bits per frame measure for the encoded current frame;

(3) means for updating the target bits per frame parameter in accordance with the bits per frame measure for the encoded current frame; and

(4) means for repeating the processing of means (a)(11), (b)(1) through (b)(4), and (c)(1) through (c)(3) for a next video frame.

12. The apparatus of claim 11, wherein means (a)(10) comprises means for initializing the target bits per frame parameter in accordance with a specified target bit rate and a specified target frame rate.

13. The apparatus of claim 7, wherein the apparatus comprises a host processor.

14. The apparatus of claim 7, wherein the apparatus comprises a pixel processor.

15. A system for encoding video signals, comprising:

(a) a video source for providing a current video frame; and

(b) a conferencing system for;

(1) receiving the current video frame;

(2) selecting a quantization level for the current video frame in accordance with a plurality of mappings, wherein each mapping correlates an activity measure with a bits per frame measure and each mapping corresponds to a quantization level of a plurality of quantization levels; and

(3) encoding the current video frame in accordance with the selected quantization level.

16. The system of claim 15, wherein the conferencing system:

determines an activity measure for the current video frame; and

selects the quantization level for the current video frame in accordance with the plurality of mappings and the activity measure.

17. The system of claim 15, wherein:

the current video frame is divided into a plurality of regions, each region being designated for intra encoding or for inter encoding; and

the conferencing system;

selects an intra quantization level and an inter quantization level for the current video frame in accordance with a plurality of intra mappings and a plurality of inter mappings, wherein;

each intra mapping correlates an intra activity measure with a bits per frame measure and each intra mapping corresponds to an intra quantization level of a plurality of intra quantization levels; and

each inter mapping correlates an inter activity measure with a bits per frame measure and each inter mapping corresponds to an inter quantization level of a plurality of inter quantization levels; and

encodes the current video frame in accordance with the selected intra quantization level and the selected inter quantization level.

18. The system of claim 15, wherein the conferencing system:

provides one or more test video sequences, each test video sequence comprising one or more test video frames;

encodes each test video frame of each video sequence with intra encoding, for each intra quantization level of a plurality of intra quantization levels;

generates an IntraSAD measure for each intra encoded test video frame;

determines a bits per frame measure for each intra encoded test video frame;

generates an intra mapping between the IntraSAD measures and the bits per frame measures, for each intra quantization level;

encodes each test video frame of each test video sequence with inter encoding, for each inter quantization level of a plurality of inter quantization levels;

generates an InterSAD measure for each inter encoded test video frame;

determines the bits per frame measure for each inter encoded test video frame; and

generates an inter mapping between the InterSAD measures and the bits per frame measures, for each inter quantization level.

19. The system of claim 18, wherein the conferencing system:

initializes a target bits per frame parameter;

receives the current video frame, wherein the current video frame is divided into a plurality of regions, each region being designated for intra encoding or for inter encoding;

generates an average IntraSAD measure for the current video frame;

generates an average InterSAD measure for the current video frame;

determines a percentage of intra regions and a percentage of inter regions for the current video frame;

selects an intra quantization level and an inter quantization level for the current video frame in accordance with the target bits per frame parameter, the plurality of intra mappings, the plurality of inter mappings, the average IntraSAD measure, the average InterSAD measure, the percentage of intra regions, and the percentage of inter regions;

encodes the current frame in accordance with the selected intra quantization level and the selected inter quantization level;

determines the bits per frame measure for the encoded current frame; and

updates the target bits per frame parameter in accordance with the bits per frame measure for the encoded current frame.

20. The system of claim 19, wherein the conferencing system initializes the target bits per frame parameter in accordance with a specified target bit rate and a specified target frame rate.

21. The system of claim 15, wherein the conferencing system comprises:

(1) a host processor; and

(2) a video board, wherein;

the video board receives the current video frame from the video source and encodes the current video frame; and

the host processor controls the operations of the video board.

22. The system of claim 21, wherein the video board comprises:

a video analog-to-digital converter for receiving unencoded analog video signals corresponding to the current video frame from the video source and for generating unencoded digital video signals;

a video capture module for capturing the unencoded digital video signals and generating unencoded captured video signals;

a memory device for storing the unencoded captured video signals;

a pixel processor for generating an encoded video frame corresponding to the current video frame from the unencoded captured video signals and storing the encoded, video frame in the memory device; and

a bus interface for transmitting the encoded video frame to the host processor.