US 2014/0177709 A1Published application

Image encoding apparatus, image encoding method and computer program

AssigneeCanon Kabushiki Kaisha

InventorHideaki Hattori

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Abstract

To reduce power consumption in an encoding process without extremely lowering encoding efficiency, a chrominance of each pixel of a prediction block is derived as a reference chrominance block according to a chrominance intra prediction mode from a reference chrominance sample representing a chrominance of a pixel necessary for intra encoding, a difference between the reference chrominance block and a chrominance sample of an input encoding block is derived as a chrominance prediction residual, and an evaluation value of the chrominance prediction residual is derived. This process is performed to a candidate of the chrominance intra prediction mode adoptable irrespective of a luminance intra prediction mode. The chrominance intra prediction mode corresponding to the evaluation value when this evaluation value is equal to or smaller than a threshold is adopted as the chrominance intra prediction mode of the prediction block.

Claims15

Dependent claims

An image encoding apparatus which compresses an input image with respect to each encoding block and outputs an encoded stream, comprising:

a first intra-screen prediction unit configured to, with respect to a plurality of candidates of a first prediction mode, derive a first prediction residual block which is a difference between a value of a first image component of a block obtained by performing intra-screen prediction to the first image component in the first prediction mode and a value of the first image component in a block obtained from the first image component of the input image, per a prediction block corresponding to the encoding block or a plurality of prediction blocks obtained by dividing the encoding block;
a second intra-screen prediction unit configured to, with respect to a plurality of candidates of a second prediction mode, derive a second prediction residual block which is a difference between a value of a second image component of a block obtained by performing intra-screen prediction to the second image component in the second prediction mode and a value of the second image component in a block obtained from the second image component of the input image, per the prediction block corresponding to the encoding block or the plurality of prediction blocks obtained by dividing the encoding block;
and
a prediction mode determination unit configured to determine the second prediction mode to be used in the intra-screen prediction for the second image component of the input image, on the basis of an evaluation value representing an estimated generated code amount of the second prediction residual block obtained for the candidate of the second prediction mode,
wherein, in a case where the evaluation value representing the estimated generated code amount of the second prediction residual block for the candidate of a specific second prediction mode among the candidates of the second prediction mode satisfies a predetermined condition, the prediction mode determination unit determines the candidate of the specific second prediction mode at a time when the evaluation value satisfying the predetermined condition is obtained, as the second prediction mode to be used in the intra-screen prediction for the second image component of the input image.

2 more elements

An image encoding method which compresses an input image with respect to each encoding block and outputs an encoded stream, comprising:

a first intra-screen prediction step of, with respect to a plurality of candidates of a first prediction mode, deriving a first prediction residual block which is a difference between a value of a first image component of a block obtained by performing intra-screen prediction to the first image component in the first prediction mode and a value of the first image component in a block obtained from the first image component of the input image, per a prediction block corresponding to the encoding block or a plurality of prediction blocks obtained by dividing the encoding block;
a second intra-screen prediction step of, with respect to a plurality of candidates of a second prediction mode, deriving a second prediction residual block which is a difference between a value of a second image component of a block obtained by performing intra-screen prediction to the second image component in the second prediction mode and a value of the second image component in a block obtained from the second image component of the input image, per the prediction block corresponding to the encoding block or the plurality of prediction blocks obtained by dividing the encoding block;
and
a prediction mode determination step of determining the second prediction mode to be used in the intra-screen prediction for the second image component of the input image, on the basis of an evaluation value representing an estimated generated code amount of the second prediction residual block obtained for the candidate of the second prediction mode,
wherein, in a case where the evaluation value representing the estimated generated code amount of the second prediction residual block for the candidate of a specific second prediction mode among the candidates of the second prediction mode satisfies a predetermined condition, the prediction mode determination step determines the candidate of the specific second prediction mode at a time when the evaluation value satisfying the predetermined condition is obtained, as the second prediction mode to be used in the intra-screen prediction for the second image component of the input image.

2 more elements

Dependencies are inferred from the claim text.