Makoto M. Miyahara

Objective picture quality scale (PQS) for image coding

A new methodology for the determination of an objective metric for still image coding is reported. This methodology is applied to obtain a picture quality scale (PQS) for the coding of achromatic images over the full range of image quality defined by the subjective mean opinion score (MOS). This PQS takes into account the properties of visual perception for both global features and localized disturbances. The PQS closely approximates the MOS, with a correlation coefficient of more than 0.92, as compared to 0.57 obtained using the conventional weighted mean-square error (WMSE). Extensions and applications of the methodology and of the resulting metric are discussed.

Comparison of image coding techniques with a picture quality scale

A newly developed picture quality scale (PQS) provides a numerical measure of image quality for monochrome images well correlated with the mean opinion score. In this paper, we report some results on the evaluation and comparison of image coding methods with such an objective quality measure. The emphasis is given here to the evaluation of the quality of JPEG coding standard. We also review and discuss the important new areas of research that an objective distortion measure now makes possible.

Objective picture quality scale for color image coding

This paper considers an objective picture quality scale for color images (PQScolor). PQScolor approximates the mean opinion score satisfactorily, it takes into account the color perception by using color difference and the properties of visual perception for global features and for localized disturbances. There are two type systems, PQScolor1 is based on Godloves color difference and PQScolor2 is based on H, V, C signal difference. The correlation coefficient between PQScolor (1, 2) and MOS is more than 0.9, which is very high compared to the value 0.34 obtained for the mean color difference scale.

Objective picture quality scale for video images (PQSvideo): definition of distortion factors

We propose a PQSvideo (Picture Quality Scale for moving image), a method of objective quality assessment for coded moving images. We expect that the proposed PQSvideo approximates subjective assessment well. In PQSvideo, we define essential distortion factors considering not only global distortions (such as random noise) but also distortions on local features. Then, we describe each distortion metrically considering human visual perception. The PQSvideo is given by a linear combination of define each essential distortion factor, utilizing the principal component analysis method and the multiple regression analysis method between quantity of each essential distortion factor and MOS (Mean Opinion Score) obtained by assessment test. We have confirmed that the PQSvideo approximates MOS successfully.

Corresponding affect between music and color

We propose a new method to realize the media conversion between music and image according to the feeling. In this research, we have focused on color combination and corresponded the affect evoked from music with color combination in subjective assessment. As the result, the affective mapping table between music and color combination has been obtained and the reliability of the obtained mapping table has been verified in the viewpoint of media conversion. The selected color combinations based on the mapping table evoke the affect like the musical affect: the maximum concordance rate between music and color combination is 70%. In this research, it is clarified that (1) musical affect and color affect have strong similarity each other, and (2) color combination can be applied to the sophisticated media conversion between music and image.

Important distortion factors in the encoding of very high quality images

The determination of an objective quality scale for image coding that corresponds to the subjective evaluation of quality is a long standing problem that has eluded researchers for many years because of its complexity. As a consequence, SNR, which is recognized as an inappropriate method for evaluating image coding, has been widely used for convenience. Recently, several of the authors have developed a new approach to the quantitative determination of image quality, defining a picture quality scale (PQS) that correlates well with subjective ratings, for mean opinion scores (MOS) in the range of 2 to 4. In this work, we extend and specialize these results for the case where the quality requirements become very high and where the distortion should be barely perceptible. We consider the detailed spatial distortion maps, which are the local contributions for distortion factors that make up PQS, as spatial indicators of perceptible distortions. We determine the applicability of these distortion maps to the type of distortions that remain perceptible at high quality. We propose some modifications to the PQS metric that would apply at high quality. The experimental results are established for images processed using the JPEG coding standard.

Consideration on objective estimation method for quality of video coding

The main media in multimedia communication are moving images, and the development of the objective quality evaluation method of the color moving image is strongly hoped for. In this research, as the preparatory steps for the development of the objective quality evaluation method, the subjective evaluation experiment was done using the semantic differential method, to clarify factors of the subjective quality evaluation in which the moving image was encoded using the MC plus DCT. These factors are the basic components which evaluate objectively the picture quality. Moreover, the difference of the evaluation factors was analyzed, it compared with the result of the subjective evaluation experiment of the intra-frame coding and the inter-frame coding. Next, the subjective evaluation experiment was done by the EBU method and the relation between the subjective evaluation factors which is derived from the SD method and the scale of the quality degradation (MOS) was investigated.

Optimum partition of two-dimensional frequency band with human visual sensitivity for subband image coding

This paper proposes a method of optimizing the partition of a two-dimensional frequency band so that high-quality reconstructed images are obtained by subband image coding. This partitioning is derived by minimizing the weighted quantization noise power with human visual sensitivity. To simplify the coding system, the structure of the filter bank is analyzed. The band partition parameters which makes the filter bank more efficient are selected, based on experimental results for actual images. The quality of images reconstructed by the proposed method is evaluated by using the relationship between the weighted quantized noise power and their entropy. The proposed method is subjectively evaluated by comparing it with a nonweighted method and the DCT method.

Two-dimensional optimum band partition based on band blocks for subband image coding

Subband coding is important (1) to decompose an input signal into an adequate set of subbands considering the property of an input signal and (2) to assign an adequate bits in proportion with the power of each subband signal. Investigation of auto-correlation characteristics of several kinds of images reveals us an isotropic correlation model. Based on this theoretical image model, we have derived the optimum band partition that minimizes the quantization noise power of the reconstructed signal at the receiving end. In order to apply the above theoretical optimum band partition to the image coding, we propose the optimum band partition scheme based on an idea of a set of band blocks, and we present the calculation algorithm with the low computational complexity to determine the optimum band partition. Also, we propose two methods to exploit the non-stationary nature of images, and the filter bank configuration to realize the optimum band partition including these methods. The proposed optimum band partition shows better result than that of the blocking DCT in obtaining the higher compression rate and the higher image quality.

Extra high quality imaging system

In order to obtain an extra high quality electronic imaging system, new important physical factors and system characteristics are considered and partly tested in addition to such traditional characteristics as the frequency characteristic and the signal to noise ratio. In particular, we consider the effect of the gama on the preservation of the quality, and the precision in the addition of R, G and B components in a display CRT, needed to maintain the high order global impression of an original image. The problem is discussed systematically both on the basis of measurements in the uniform lightness-chromaticity scale system and of high order psychophysical effects.