US 7,453,938 B2Granted

Target bitrate estimator, picture activity and buffer management in rate control for video coder

AssigneeApple Inc.

InventorsBarin Geoffry Haskell, Adriana Dumitras, James Normile, Hsi-Jung Wu, Xiaochun Nie, Atul Puri

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Abstract

A rate control system is disclosed for video coding applications. The rate controller assigns a quantization parameter for video data in a picture in response to complexity indicators indicative of spatial complexity, motion complexity and/or bits per pel of the picture. A virtual buffer based quantizer parameter is proposed based on a virtual buffer fullness analysis and a target rate estimate, which is derived from the complexity indicators. A second quantizer parameter is proposed from a linear regression analysis of quantizer parameters used to code previously coded pictures of similar type (e.g., I pictures, P pictures or B pictures). A coding policy decision unit defines a final quantizer parameter from a comparison of the two proposed quantizer parameters.

Claims4

Dependent claims

A quantizer selection method, comprising:

calculating a normalized average activity level of a picture from on image information of the picture,
adjusting a base quantizer value according to the picture's normalized average activity level, and
selecting a quantizer value for the picture based on the adjusted quantizer value,
wherein the calculating comprises:
for a plurality of macroblocks in the picture, calculating variances of image data for a plurality of blocks therein,
from minimum variance levels of the macroblocks, calculating minimum activity levels of the macroblocks, wherein the minimum activity of each macroblock is calculated as:
actmin=1+min(blkvar1, blkvar2, blkvar3, blkvar4), where blkvar represents the variances of 8×8 blocks within a respective macroblock, and
normalizing the minimum activity levels of the macroblocks, wherein the normalized minimum activity per macroblock is calculated as:
actnorm
=
(
2
×
act
⁢
⁢
min
)
+
act
⁢
⁢
min
⁢
⁢
avg
act
⁢
⁢
min
+
(
2
×
act
⁢
⁢
min
⁢
⁢
8
⁢
⁢
avg
)
where actminavg is a sum of actmin values for all macroblocks in a previously processed picture and the actnorm values for all macroblocks in the picture are averaged to obtain the normalized average activity level of the picture.

43 more elements

Dependencies are inferred from the claim text.

Facts

Application: 10/812,062Filed 30 Mar 2004 · us provisional application
Priority: 6 Feb 2004
Published: US 2005/0175093 A111 Aug 2005
Granted: 18 Nov 2008
Term ends: Not estimatedThe source records don’t support an estimate.

Classification17 codes

H04N 19/33
Using hierarchical techniques, e.g. scalability: in the spatial domain
H04N 19/107
Selection of coding mode or of prediction mode: between spatial and temporal predictive coding, e.g. picture refresh
H04N 19/115
Characterised by the element, parameter or selection affected or controlled by the adaptive coding: selection of the code volume for a coding unit…
H04N 19/117
Characterised by the element, parameter or selection affected or controlled by the adaptive coding: filters, e.g. for pre-processing or…