Hiroaki Sobagaki

Opponent-colors responses in the visually evoked potential in man

Abstract The responses of visually evoked cortical potential (VECP) of three observers with normal-color vision were measured for 10 different spectral stimuli ranging from 400 to 700 nm with the equal retinal illuminance of 300 td. These responses were analyzed by use of the principal component analysis, and the results obtained are as follows: (1) Opponent-colors responses were found for two of the three observers which were similar to those derived by Jameson-Hurvich on the basis of psychophysical methods. (2) The VECP responses for another observer were almost independent of the different spectral stimuli applied. This was interpreted as a noncolor-coding observer, as shown by Shipley. (3) The same analysis was applied to the VECP responses measured by Shipleyet al. (1968). Though the waveforms are significantly different from those by the present authors, similar opponent-colors responses were also derived.

Prediction of experimental results on additivity-law failure

Experimental results on additivity-law failure observed by direct brightness matching are estimated for various combinations of two spectrum colors. The estimations are made by using the prediction equation of the Brightness/Luminance (B/L) ratio effect on chromatic colors, which is based upon the Variable Chromatic Color (VCC) method for the effect. The predicted results confirm the existence of the two types of additivity-law failures called enhancement or cancellation, already reported by several researchers. The prediction equation also clarifies that the effect of additivity-law failure does not change for a wide change of adapting luminance used in observation. Both B/L effect and additivity-law failure can be estimated quite nicely by the same prediction equation without making any modification to it. The Helmholtz–Kohlrausch effect can imply both effects in its wide definition.

On the field trials of CIECAM97s and its model structure

The structure of the color-appearance model CIECAM97s is examined. The problems with its chromatic-adaptation transform, called the Bradford transform, are discussed in detail. The contradictions existing between the measures at various stages of CIECAM97s are described, which are ea-eb, saturation s, chroma C, and colorfulness M. The main contradictions are (1) the inversion of chromatic components between test and reference colors at different measures; and (2) the similarity between chroma and colorfulness found in the experiments done under different adapting illuminances. The structural problems in CIECAM97s are clarified by comparing its predictions with those using CIECAT94LAB, which consists of the CIE chromatic-adaptation transform published in 1994 and the CIELAB formula.

Estimation of Spectral Reflectance Distributions of Highly Saturated Colors in Munsell Color Order System

In the previous study (Sobagaki et al., 1983) , we applied principal component analysis to the measured spectral reflectance distributions (SRDs) of the JIS Z 8721 color chips, and proposed a reconstitution method for deriving the SRD corresponding to any specified Munsell renotation. However, the SRD generated by the method did not satisfy the object color condition (0•...p(ƒÉ)•...1) for highly saturated colors, where p (X) denotes to the SRD. In this paper, we derive the SRD satisfying the object color condition in the region of highly saturated colors. The SRD of highly saturated colors is given by combining the SRD obtained by the reconstitution method with that of optimal colors and with those of achromatic colors. This method was applied to all the highly saturated colors specified in JIS Z 8721 to provide the standard colorimetric values under CIE standard illuminant D65.

ON THE NONLINEARITY OF CHROMATIC RESPONSES BASED ON ERG DATA IN MAN

ERG data measured by Riggs et al. was analysed by use of some multivariate techniques. The results were compared with those derived by their trial and error method based on the psychophysical point of view, especially in the estimation of chromaticity diagram. The multivariate techniques applied are Torgerson-Gower method(i. e. principal coordinate analysis), Shepard-Kruskal method(well known nonmetric multidimensional scaling), and a new method proposed by one of the authors, T. I. The features of the three methods were discussed during the course of analysing the ERG data. The chromaticity diagram predicted in the present study satisfied the psychophysical requirements better than that predicted by Riggs et al. In addition, the present analysis allowed to estimate the noise component in the observed ERG data and clarified their latent structures.

A Theoretical Classification of Metameric Pairs Including Fluorescent Samples

Along the guidelines for field-trials of the proposal for assessing the performance of artificial daylight by the CIE TC-1.3 (Colorimetry), the following studies were made for ultraviolet assessment of the light sources.(1) Metameric pairs including fluorescent samples are theoretically classified into eight categories, according to whether each of themetameric samples is fluorescent or nonfluorescent and according to whether its spectral reflectance function is zero or not. These eight categories are summarized into three fundamental groups.(2) Among these eight kinds of metameric pairs, the following pairs is found to be most adequate for ultraviolet assessment of artificial daylight: The pairs consists of two metameric samples which have the same spectral reflectance curves and the same spectral coefficients of fluorescence emission but different spectral coefficients of quantum absorption.(3) The differences are clarified among three methods of assessment for artificial daylight by use of fluorescent samples. These methods are (a) the assessment of color rendering property by Terstiege, (b) the assessment by Berger and Strocka, and (c) the proposed assessment by use of the metameric pairs. It is described that the method (a) does not give the exact assessment of ultraviolet range of the light sources.

Studies on Color Rendering and Illuminant Metamerism (Part 3)

Based on the spectral power distributions of actual fluorescent lamps (about 6, 500 K in color temperature), the amounts of line spectra were pre-assigned as 80.0 to 405 nm, 200.0 to 436 nm, 100.0 to 546 nm and 30.0 to 578 nm, respectively.The existence of the spectral power distributions of the test illuminants with these amounts of line spectra, which fulfil the following requiremnts further was examined.(1) With respect to any of the reference illuminatnts, the test illuminants have the same chromaticity coordinates and the general color-rendering index of Ra=100, provided that the spectral power distributions of the reference illuminants are normalized as 100 or near 100 at the wavelength of 560 nm.(2) In addition to the requirement 1), the minimum value of the sum of squares is expected with respected to the difference in spectral power distributions between the reference and the test illuminantsThese conditions are reduced to solving the linear homogeneous equations derived by applying the Lagrange multiplier method. The spectral power distributions Jt (λ) of the test illuminant was obtained with respect to the CIE standard illuminant C as the reference, which also satisfied the above two requirements.However, the computed results give an imaginary spectral power distribution which corresponds to negative radiations in some of the visible spectra. This might suggest the impossibility to realize the general color rendering index of Ra=100 with a fluorescent lamp having the pre-assigned amounts of line spectra shown above.