Field of the Invention
The present invention relates to moving image coding devices, moving image decoding devices, moving image coding methods and moving image decoding methods.
Description of the Related Art
In the standard methods related to video compression represented by Non-patent reference 1 and Non-patent reference 2, in in-screen prediction (intra prediction), a method is used in which a reference value, which is a decoded value of an adjacent coded block, is used as a prediction value for a pixel located at a position along a prediction direction. With this method, a plurality of prediction directions are defined in advance, and coding performance can be improved by applying an appropriate prediction direction.
Non-patent reference 3 and Non-patent reference 4 describe a method in which, in the aforementioned intra prediction, the reference value is weighted based on a pixel value of a neighboring decoded pixel, rather than using a simple copy of the reference value. Non-patent reference 5 describes a method of weighting a reference pixel based on a result of analysis that corresponds to the distance from the reference pixel.    Non-patent reference 1: “High Efficiency Video Coding (HEVC) text specification draft10,” JCT-VC 12th meeting, JCTVC-L1003 v34, January 2013.    Non-patent reference 2: Joint Video Team (JVT) of ISO/IEC MPEG and ITU-T VCEG, “Text of ISO/IEC 14496-10 Advanced Video Coding,”    Non-patent reference 3: L. Wang, L.-M. Po, Y. Uddin, K.-M. Wong and S. Li, “A Novel Weighted Cross Prediction for H.264 Intra Coding,” ICME2009.    Non-patent reference 4: S. Yu, Y. Gao, J. Chen and J. Zhou, “Distance-based Weighted prediction for H,264 Intra Coding,” ICALIP2008.    Non-patent reference 5: R. Cha, O. C. Au, X. Fan, X. Zhang and J. Li, “Improved Combined Intra-Inter Prediction using Spatial-Variant Weighted Coefficient,” ICME2011.
With the methods described in Non-patent references 1 and 2, when generating the prediction value based on the prediction direction in the intra prediction, the correlation of the pixel values among pixels decreases as the distance between the pixels increases. For this reason, if the block size of a processing block increases, prediction performance decreases the further the distance of a pixel from the reference pixel is.
Then, a reduction in the block size of the processing block is conceivable. This can prevent an increase in the distance between pixels, and accordingly a decrease in the prediction performance can be suppressed. However, a reduction in the block size of the processing block increases the number of blocks, resulting in an increase in control information to be provided to each processing block, and there is a concern that compression performance cannot be improved.
With the methods described in Non-patent references 3 and 4, as for a pixel whose distance from a coded pixel is small in a processing block, improvement in compression performance can be expected. However, as the distance from a coded pixel increases in the processing block, improvement in the compression performance cannot be expected.
Meanwhile, with the method described in Non-patent reference 5, as mentioned above, a reference pixel is weighted based on a result of analysis that corresponds to the distance from the reference pixel. For this reason, improvement in compression performance can be expected even if the distance from the reference pixel is large. However, the method described in Non-patent reference 5 uses information of an inter coding frame when performing the aforementioned analysis. For this reason, improvement in compression performance cannot be expected in the intra prediction.