Hiroaki Kotera

Novel color transformation algorithm and its applications

We propose a new algorithm available to variety of real-time color space transformations : color correction for hardcopy system, perceptual color control in CIE-LAB space, color coordinate conversions, and color recognition. This algorithm consists of color look up tables and a new 3D color space interpolator. This interpolator makes it easy to design a simple real-time color processor. The simulation shows how the flexible transformations can be performed without degrading the color and tone.

Analysis of color gamut for hardcopy based on Neugebauer theory

The gamut of color in digital color printer is discussed with a simple color mixing model based on Neugebauer theory. A colored halftone area is composed of at most 8 colored dots: Cyan, Magenta, Yellow, Red, Green, Blue, White, and Black. It is shown that a color gamut and a color-locus change by the 2 colored dot overlay method. Typical color changes in thermal transfer printer were observed experimentally in coincidence with theotretical estimations. The dot allocation of dither matrix causes the significant changes in the hue of red tone and the gamut of bluish colors.

The New Color Image Processing Techniques for Hardcopy

This paper addresses to provide some of the new image processing techniques for color hardcopy. The first requirement for high quality color imaging, is how to reproduce a continuous tone. In the actual printing systems, we often encounter the false contours caused by a lack of gray levels or a jump of dot density. Here, we present a tone smoothing method using an improved pseudo-noise modulation as a countermeasure for such a printer with discontinuities in gray scale reproduction. The second requirement is to get the correct color rendition. We discuss two models on color correction and show the practical applications for full color printing. As the third requirement, a function to adjust color-tone as you like, will be needed for the future hardcopies and we shortly discuss the color adjusting problem based on human color perception. Lastly, we report our latest works on the new color coding technique, which can reconstruct a full color image from a single color image by utilizing the strong correlation characteristics among RGB signals.

Indirect estimation of spectral response and its colorimetric evaluation.

カラー画像処理システムの入力部として, スキャナの色分解フィルタの設計は重要である.測色的な色再現を目的とするシステムでは, スキャナの3色分解系は原画の測色的な三刺激値を正しく伝達することが要求される.しかしながら, 実際の装置の色分解特性は, 種々の構成要素の分光特性を総合して得られるもので, 製作後の装置については, その総合特性を直接分光測定することが容易でないために, 測色的な評価が充分に行われないまま使用されていることが多い。本論文では, 分光器などを用いることなく, スキャナの3色分解信号を外部から観測するだけで, 間接的に内部の分光感度特性を推定する方法を論じ, 実際のスキャナの測色的評価に適用した実験結果を報告する.筆者らのスキャナでは, 測色係数q≅0.9が得られ, ほぼ満足すべき特性をもつことが確認された.本方法は, フィルタ設計ミスの修正や製品の検査に有効である.