Naoyuki Awano

Perceptual coding for a super high-definition video based on subjective assessment of viewing distance

Very high-resolution video systems, such as 4K (3840×2160), enable a very close viewing distance that is almost the same as the picture height. This technology enables high-reality systems in homes to be realized. However, the very short distance causes significantly different views across the picture, and uniform processing for the picture may not always be the best choice. Here, we calculate the actual view size of a pixel, which depends on the pixel position in close viewing. We proposed the perceptual coding methods using pre/post-processing for the picture to be coded. It is a quantization control by a contrast change. However, the control of quantization should be decided based on the perceptual performance between pixel size and quantization. Therefore, we carried out subjective assessment about this. The bit rate reduction is checked for each method. The 4K resolution processing is realized by four patterns of HDTV picture coding with AVC. As the results of these experiments, it is recognized that the bit rate reduction 15 percent by the optimal coding.

Evaluation and simplification of objective estimation for the quality of HDR images

High dynamic range (HDR) images that include large differences in brightness levels are studied to address the lack of knowledge on the quality estimation method for real HDR images. For this, we proposed the local peak signal-to-noise ratio (LPSNR), using the maximum value of neighboring pixels. Next, we proposed an objective estimation method that considers spatial frequency characteristics based on the actual brightness. In this method, we used 2D filter on an FFT for spatial frequency weighting. However, in the case of whole picture processing, the rational evaluation is difficult. To solve this problem, we divide a picture to small area, the weighting processing applied each area. Furthermore, we propose more simplified method without FFT/IFFT. In order to confirm performance of these objective estimation methods, we compared the results of the objective estimation with a subjective assessment. The results of the correlation of partial adaptive method processing does not give significant difference. The correlation of simplified method shows its usefulness.