Katsuhiro Kanamori

Fast color processor with programmable interpolation by small memory (PRISM)

We present a novel color processor with programmable interpolation by small memory (PRISM). The input/output signals to/from the devices are flexibly converted by a 3-0 look-up table (LUT) with a PRISM interpolator. The PRISM architecture provides a simple computation algorithm with sufficient accuracy. The performance of PRISM interpolation is compared with other conventional methods. In practice, PRISM is less complicated than CUBE and PYRAMID, and more accurate than PYRAMID and TETRAHEDRON. PRISM cuts the memory size of LUT drastically to an orderof iO compared with a full-size LUT method and brings with it a large-scale integration color processor operating at a higher than video rate. The PRISM structure is the most suitable for the perceptual color spaces such as YCrCb or CIELAB and very useful for device-independent color reproduction and transmission. Typical applications by a PRISM color processor are presented.

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.

Averaged subtracted polarization imaging for endoscopic diagnostics of surface microstructures on translucent mucosae

Abstract. An endoscopic image processing technique for enhancing the appearance of microstructures on translucent mucosae is described. This technique employs two pairs of co- and cross-polarization images under two different linearly polarized lights, from which the averaged subtracted polarization image (AVSPI) is calculated. Experiments were then conducted using an acrylic phantom and excised porcine stomach tissue using a manual experimental setup with ring-type lighting, two rotating polarizers, and a color camera; better results were achieved with the proposed method than with conventional color intensity image processing. An objective evaluation method that uses texture analysis was developed and used to evaluate the enhanced microstructure images. This paper introduces two types of online, rigid-type, polarimetric endoscopic implementations using a polarized ring-shaped LED and a polarimetric camera. The first type uses a beam-splitter-type color polarimetric camera, and the second uses a single-chip monochrome polarimetric camera. Microstructures on the mucosa surface were enhanced robustly with these online endoscopes regardless of the difference in the extinction ratio of each device. These results show that polarimetric endoscopy using AVSPI is both effective and practical for hardware implementation.

Interpolation errors on gray gradations caused by the three-dimensional lookup table method

Three-dimensional table interpolation techniques are now widely used in color management systems. These techniques are practical because complicated color conversions such as gamma conversion, matrix masking, under color removal, or gamut mapping can be executed at once by use of a three-dimensional lookup table (3D LUT). However, in some cases, the resultant interpolated reproduction of gradation has visible artifacts that degrade neutral and color gradations. Several research works concerning interpolation accuracy have been published. However, those articles have focused on an average color difference derived from experiments based on very few types of color conversions with no theoretical explanation. This paper describes a theoretical evaluation of errors and reproduced gradation curves using three-dimensional interpolation for several nonlinear color conversions. Two types of errors; conventional error and ripple error that is difference between piece-wise linear approximation and interpolated curves are defined, and gray gradation is used for an input image. The errors with a tetrahedral interpolation technique are also examined. Several nonlinear color conversions are tested and significant ripples have been found in case of the matrix-gamma with negative coefficients and minimum (MIN) function. The error goes down with decreasing of the distance between the lattice points (D), however, the decreasing rate is quite different. From these analyses we can get useful information about optimal 3D LUT sizes and which conversions are suitable for three-dimensional interpolation.

Image enhancement of surface micro-structure on mucosa for polarimetric endoscopy

This paper describes a novel image processing method for endoscopy that enhances the appearance of microstructures on mucosa. The new technique employs two pairs of parallel- and crossed-nicols polarimetric images, from which an averaged subtracted polarization image (AVSPI) is calculated. Experiments were first executed using a manual experimental setup with ring-type lighting, two rotating polarizers and a color camera. A new objective evaluation method that uses texture analysis (GLCM) was developed and applied to evaluation of the enhanced microstructure images. Experiments using excised porcine stomach tissue showed better results than with conventional color intensity image processing. Next, an online rigid-type polarimetric endoscope system using a polarized ring-shaped LED and a special three-CCD color polarimetric camera was developed. The two types of equipment described above are quite different as to extinction ratio values, but show similarly enhanced image quality. Our results show that polarimetric endoscopy is not only effective but also practical for hardware implementation.

Color management system with multilayer perceptrons

This paper has two objectives. The first is to explain our color reproduction procedure, especially our new gamut check and mapping method and comparative experimental results on it. The second is to discuss availability and effectiveness of multilayer perceptron (MLP) in the color reproduction fields. We will show problems and merits of MLP and its learning through experiments.

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.

Fish freshness estimation using eye image processing under white and UV lightings

A non-destructive method of estimating the freshness of fish is required for appropriate price setting and food safety. In particular, for determining the possibility of eating raw fish (sashimi), freshness estimation is critical. We studied such an estimation method by capturing images of fish eyes and performing image processing using the temporal changes of the luminance of pupil and iris. To detect subtle non-visible changes of these features, we used UV (375 nm) light illumination in addition to visible white light illumination. Polarization and two-channel LED techniques were used to remove strong specular reflection from the cornea of the eye and from clear-plastic wrap used to cover the fish to maintain humidity. Pupil and iris regions were automatically detected separately by image processing after the specular reflection removal process, and two types of eye contrast were defined as the ratio of mean and median pixel values of each region. Experiments using 16 Japanese dace (Tribolodon hakonensis) at 23℃ and 85% humidity for 24 hours were performed. The eye contrast of raw fish increase non-linearly in the initial period and then decreased; however, that of frozen-thawed fish decreased linearly throughout 24 hours, regardless of the lighting. Interestingly, the eye contrast using UV light showed a higher correlation with time than that using white light only in the case of raw fish within the early 6- hour period postmortem. These results show the possibility of estimating fish freshness in the initial stage when fish are eaten raw using white and UV lightings.

Inherent limitations on specular highlight analysis

We analyse specular highlight modelling using microfacet-based physics illumination models. The ability to perform effective modelling is shown to depend on the ratio of the quantisation noise, ε, in the normal data to the object’s surface roughness parameter, m. We characterise how the accuracy degrades with increasing normal vector noise, when fitting is done in the Least Mean Squares sense. We show that it is not possible to accurately characterise sharp specular highlights, unless ε is very much less than m, and give examples of the practical implications of this theoretical result. We observe that the recently reported frequency-domain approaches can obscure this problem. We also present a novel characterisation of the importance of the geometric attenuation term in the microfacet models.