Spatial intra prediction has been added recently to the latest video coding standard H.264/AVC. In the intra
prediction of H.264/AVC, there are 9, 9 and 4 prediction modes for 4×4, 8×8 and 16×16 blocks, respectively.
Prediction signals are generated by using one or several reference pixels. The value of a reference pixel is copied
as the prediction value. In some prediction modes, we calculate a weighted mean by averaging several pixels.
The same prediction value is copied to several of the pixels lying in the prediction direction. However, if original
image has patterns like gradations, the residual energy could increase which would result in low coding efficiency.
In this paper, we propose a new intra prediction that generates prediction signals with a spatial gradient to deal
with this problem. Simulation results show that it improves the picture quality and reduce the bit-rate by about
0.14 dB and 1.0 % on average for CIF sequences, respectively. It is also confirmed that our method is effective
at high bit-rates.
In this paper, we propose a multi-frame synchronization method which has sufficient scalability, and describe an SHR codec system we have developed that uses MPEG-2 codecs and a multi-HDTV frame synchronizer
based on our method.
Intra coding for lossy block base transform video coding and still picture coding has been studied. In H.264, pixel domain prediction is applied, where all pixel values in a block are predicted from decoded images in surrounding blocks. There are some advantages in pixel domain prediction comparing with DCT domain prediction. One thing is
that in pixel domain prediction, residual data at block boundaries becomes smaller. On the other hand, in pixel base prediction scheme for lossless coding, each pixel value is predicted from surrounding pixels generally. In Multiplicative Autoregressive Models (MAR) or JPEG-LS, each pixel is predicted from some neighboring pixels. This pixel base prediction scheme is more effective to reduce prediction error than block base prediction. In this paper, the new intra prediction method, Recursively Weighting pixel domain Intra Prediction (RWIP) method for block base transform coding is proposed. The RWIP applies similar approach to pixel base prediction scheme in order to reduce prediction error more than the conventional block base prediction scheme, especially for blur or complicated
directional edge images. This paper also demonstrates the efficiency of the RWIP over the normal intra prediction of H.264.
In image coding, the distribution of quantization error is uniform
across the transformed domain (i.e., coding error). To minimize
visually perceptible noise, the quantization step size should suit the
most sensitive area in the color space used. Consequently, we can
expect to improve the coding efficiency while achieving the same
subjective quality by adopting a perceptually uniform color space.
Currently used image coding schemes such as JPEG and MPEG, make
extensive use of the YCbCr color space. However, its perceptual
non-uniformity is significant. In this paper, we introduce the
uniform color space 'LST', which is obtained by smoothly deforming
the CIE xy chromaticity diagram with a look-up table with 333 morphing
points so that every MacAdam JND (just noticeable difference) ellipse
is mapped onto or close to a unit circle. Test color images that use
this LST color space, as well as the CIELAB, CIELUV and YCbCr spaces,
are JPEG coded. The coding algorithm itself does not need to be
changed. Subjective comparisons by six subjects of the decoded images
to the originals show the superiority of LST to the three other
spaces; the most commonly-used YCbCr was ranked last despite its
highest PSNR. No significant difference was observed between CIELUV