Kazuya Hayase

Mathematical error analysis of normal map compression based on unity condition

Normal maps play an important role in realistic 3D image rendering to express pseudo roughness of the surface. In normal map compression, z components are often eliminated and calculated from x and y components based on the unity condition to achieve high compression rate. However, there is no theoretical background of the validity of eliminating z components so far. In this paper, a mathematical mean square error (MSE) model of such normal map compression based on the unity condition is proposed. In addition, the boundary condition whether to eliminate or include the z components in compression for the better efficient encoding is demonstrated based on our error analysis model.

Theoretical Modeling of Inter-Frame Prediction Error for High Frame-Rate Video Signal

Realistic representations using extremely high quality images are becoming increasingly popular. For example, digital cinemas can now display moving pictures composed of high-resolution digital images. Although these applications focus on increasing the spatial resolution only, higher frame-rates are being considered to achieve more realistic representations. Since increasing the frame-rate increases the total amount of information, efficient coding methods are required. However, its statistical properties are not clarified. This paper establishes for high frame-rate video a mathematical model of the relationship between frame-rate and bit-rate. A coding experiment confirms the validity of the mathematical model.

Mathematical PSNR prediction model between compressed normal maps and rendered 3d images

Normal mapping is an essential rendering technique in 3D computer graphics to express detailed wrincleness and bumpy texture of the surface. As the normal mapping is increasingly utilized, compression of normal maps is becoming a significant issue. The problem is there is no quality evaluation model for lossy compressed normal maps. Therefore, in this paper, we have developed a mathematical model to analyze the characteristics between lossy compressed normal maps and 3D images rendered with them. By calculating averages of the parameters which cannot be defined uniquely and by introducing some assumptions, the model has been expressed in a simple form. The validity and generality of our model have been demonstrated by experiments. The model proposed in this paper will be helpful for deciding normal map compression strategy considering the target quality of the rendered 3D images.

Encoder design for H.264/AVC based on contrast sensitivity considering spatio-temporal direction dependency

It is really important to use the proper coding mode in the H.264 encoder, since it offers many more modes than the conventional methods such as MPEG-2. Typical H.264 encoders like JM and JSVM use squared error as the criterion of distortion for mode decision. However, squared error does not always provide a correct measure of the distortion from the viewpoint of subjective quality. In this paper, we investigate a mode decision algorithm based on the spatio-temporal contrast sensitivity model in order to improve the H.264 encoder. Our algorithm is designed considering the direction dependency of spatio-temporal frequency. Experiments show that our method can achieve average bit-rate savings of the order of 4.0 to 5.5% compared to the original JSVM. We confirm that both methods yield reconstructed images that basically have the same subjective image quality.

Generalized Theoretical Model of Relationship Between Frame-Rate and Bit-Rate Considering Low Pass Filtering Induced by Shutter Opening

Higher frame-rates are being considered to achieve more realistic representations. Since increasing the frame-rate increases the total amount of information, efficient coding methods are required. However, the statistical properties of such data has not been clarified. This paper establishes, for high frame-rate video, a mathematical model of the relationship between frame-rate and bit-rate. The model incorporates the effect of the low-pass filtering induced by shutter open. By incorporating the open interval of shutter, our model can be extended to describes the various cases of downsampling frame-rates. A coding experiment confirms the validity of the mathematical model.