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The YUV 4:2:0 format is a representative format for color images in international standards. In this format, both color difference components U and V reduce the number of pixels in the horizontal and vertical directions by one-half. Consequently, this reduction degrades the color difference components. At a relatively high bit rate, the degradation produced by reducing the number of pixels is often worse than the degradation that depends on the coding. Thus, processing to compensate for the degradation due to the format transform becomes necessary. The pixels of the color difference components reduced once on the encoding side are determined by interpolation on the decoding side. The typical interpolation methods are bilinear interpolation, bicubic interpolation, and interpolation by a finite impulse response (FIR) filter. When these interpolation methods were applied to interpolate the color difference components in the YUV 4:2:0 format, blur and lower saturation were produced in the colors in the color difference components returned to the original number of pixels. In this paper, we propose a method that uses information in the luminance component not having a reduced number of pixels to interpolate the color difference components in the YUV 4:2:0 format. Consequently, color blurring is prevented in the edges of the image, and an objective is to improve the saturation in the entire image. We based the proposed method on bilinear interpolation and bicubic interpolation, and formulated an interpolation method using the luminance component as an extended form. The proposed method and the bicubic interpolation are compared in both objective and subjective evaluations, and demonstrate the effectiveness of the proposed method. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 89(9): 1–10, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20218 [ABSTRACT FROM AUTHOR]

Since the dimensions for digital images are set by the acquisition system, digital image enlargement is indispensable when the dimensions that can be displayed are larger in the display system than in the acquisition system. Conventionally, this enlargement process was performed by interpolation. The digital image enlargement corresponds to a larger Nyquist frequency, but the frequency band that is expanded during the enlargement cannot be considered by the interpolation scheme, and blur is produced in the enlarged image. The parts where the image blur stands out subjectively are primarily the signals forming the image contours having the step edge shape and the details of the image consisting of mountain- and valley-shaped signals when viewed microscopically. Therefore, the proposed method moves the coordinate points interpolated to preserve the discontinuities of step edge signals and decides whether the interpolated points are the vertices of the mountain- or valley-shaped signals, and then moves the amplitudes of the interpolated points for creating these peak signals up or down. In other words, we explain an interpolation scheme involving the warping and biasing that randomly moves the coordinate points and the signal amplitudes, and implement digital image interpolation with improved resolution. Furthermore, the parameter settings for the proposed method are both objectively and subjectively evaluated. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 88(2): 10–21, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20095 [ABSTRACT FROM AUTHOR]