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Moving image encoding device and moving image encoding method

Moving image encoding device and moving image encoding method description/claims

1. Field of the Invention

The present invention relates to a digital image signal encoding device, a digital image signal decoding device, a digital image signal encoding method, and a digital image signal decoding method used for an image compression encoding technology or a compressed image data transmission technology.

2. Description of the Related Art

An international standard video encoding system such as MPEG or ITU-TH. 26x (e.g., “Information Technology Coding of Audio-Visual Objects Part 10: Advanced Video Coding”, ISO/IEC 14496-10, 2003: (hereinafter, referred to as Non-Patent Document 1)) has conventionally been premised on use of a standardized input signal format called a 4:2:0 format. The 4:2:0 format is a format where a color moving image signal of RGB or the like is transformed into a luminance component (Y) and two chrominance components (Cb, Cr), and the number of chrominance component samples is reduced to half of luminance components both in horizontal and vertical directions (FIG. 23). The chrominance component is inferior to the luminance component in visibility. Accordingly, the conventional international standard video encoding system has been based on the premise that the amount of original information to be encoded is reduced by downsampling chrominance components before encoding is executed as mentioned above. In video encoding for business purposes such as a broadcast material video, a 4:2:2 format for downsampling Cb and Cr components reduce the number of the components to half of that of luminance components only in a horizontal direction may be used. Thus, color resolution in a vertical direction becomes equal to luminance, thereby increasing color reproducibility compared with the 4:2:0 format. On the other hand, recent increases in resolution and gradation of a video display have been accompanied by studies on a system for performing encoding by maintaining the number of samples equal to that of luminance components without downsampling chrominance components. A format where the numbers of luminance and chrominance component samples are completely equal is called a 4:4:4 format. The conventional 4:2:0 format has been limited to Y, Cb, and Cr color space definitions because of the premise of downsampling of chrominance components. In the case of the 4:4:4 format, however, because there is no sample ratio distinction between color components, R, G, and B can be directly used in addition to Y, Cb, and Cr, and a plurality of color space definitions can be used. An example of a video encoding system targeting the 4:4:4 format is, Woo-Shik Kim, Dae-Sung Cho, and Hyun Mun Kim, “INTER-PLANE PREDICTION FOR RGB VIDEO CODING”, ICIP 2004, October 2004. (hereinafter, referred to as Non-Patent Document 2).

In a high 4:2:0 profile encoding the 4:2:0 format of AVC of the Non-Patent Document 1, in a macroblock area composed of luminance components 16×16 pixels, corresponding chrominance components are 8×8 pixel blocks for both Cb and Cr. In motion compensation prediction of the high 4:2:0 profile, block size information which becomes a unit of motion compensation prediction, reference image information used for prediction, and motion vector information of each block are multiplexed only for the luminance components, and motion compensation prediction is carried out for chrominance components by the same information as that of the luminance components. The 4:2:0 format has characteristics in color space definition that almost all pieces of structure information of an image is integrated into a (texture) luminance component, distortion visibility is lower for a chrominance component than for the luminance component, and a contribution to video reproducibility is small, and prediction and encoding of the high 4:2:0 profile are based on such characteristics of the 4:2:0 format. On the other hand, in the case of the 4:4:4 format, three color components equally hold texture information. The system for performing motion compensation prediction based on inter prediction mode, reference image information, and motion vector information depending only on one component is not necessarily an optimal method in the 4:4:4 format where the color components make equal contributions in representing a structure of an image signal. Thus, the encoding system targeting the 4:2:0 format performs different signal processing from the encoding system targeting the 4:4:4 format to execute optimal encoding, and definitions of pieces of information multiplexed in an encoded bit stream are also different. As a result, to construct a decoding device capable of decoding compressed video data of a plurality of different formats, a configuration where bit streams for signals of the formats are individually interpreted needs to be employed, thereby making a device configuration inefficient.

It is therefore an object of the present invention to provide a bit stream generation method for providing compatibility between a bit stream encoded in a Y, Cb, and Cr space as in the case of the conventional 4:2:0 format and a bit stream having no sample ratio distinction between color components such as the 4:4:4 format and obtained by compressing a video signal having freedom in color space definition, and a decoding method.

A moving image encoding device that receives, compresses, and encodes a digital moving image signal includes: a first intra prediction mode deciding unit for performing intra prediction on a signal component corresponding to a luminance component in a case where a chroma format of the input moving image signal is 4:2:0 or 4:2:2; a second intra prediction mode deciding unit for performing intra prediction on a signal component corresponding to a chrominance component in the case where the chroma format of the input moving image signal is 4:2:0 or 4:2:2; a variable length encoding unit for variable-length encoding a first intra prediction mode determined by the first intra prediction mode deciding unit or a second intra prediction mode determined by the second intra prediction mode deciding unit; a first intra prediction image generation unit for generating a first intra prediction image based on the first intra prediction mode; a second intra prediction image generation unit for generating a second intra prediction image based on the second intra prediction mode; and a encoding unit for performing transform and encoding on a predicted error signal obtained as a difference between the first intra prediction image or the second intra prediction image and corresponding color component signals of the input moving image signal. Based on a control signal for providing a chroma format type of the input moving image signal, in the case of a chroma format of 4:2:0 or 4:2:2, the first intra prediction mode deciding unit and the first intra prediction image generation unit are applied to the luminance component of the input moving image signal, and the second intra prediction mode deciding unit and the second intra prediction image generation unit are applied to the chrominance component of the input moving image signal. In the case of a chroma format of 4:4:4, the first intra prediction mode deciding unit and the first intra prediction image generation unit are applied to all color components of the input moving image signal to perform encoding, and the variable length encoding unit multiplexes the control signal as encoding data to be applied to a moving image sequence unit on a bit stream.

Encoding/decoding can be performed for the plurality of different chroma formats such as 4:2:0, 4:2:2, and 4:4:4 in a unified manner by the efficient device configuration, and mutual connectability between the video encoded data can be increased.

In the accompanying drawings:

FIG. 1 is an explanatory diagram showing a relation among a sequence, a picture, a slice, and a macroblock;

FIG. 2 is an explanatory diagram showing a common encoding process;

FIG. 3 is an explanatory diagram showing an independent encoding process;

FIG. 4 is a block diagram showing a configuration of an encoding device according to a first embodiment of the present invention;

FIG. 5 are explanatory diagrams showing intra N×N prediction modes (N=4 or 8);

FIG. 6 are explanatory diagrams showing intra 16×16 prediction modes;

FIG. 7 are explanatory diagrams showing 4:2:0/4:2:2 Cb/Cr intra prediction modes;

FIGS. 8A to 8H are explanatory diagrams showing macroblock units;

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