Vien Cheung

Characterization of trichromatic color cameras by using a new multispectral imaging technique.

We investigate methods for the recovery of reflectance spectra from the responses of trichromatic camera systems and the application of these methods to the problem of camera characterization. The recovery of reflectance from colorimetric data is an ill-posed problem, and a unique solution requires additional constraints. We introduce a novel method for reflectance recovery that finds the smoothest spectrum consistent with both the colorimetric data and a linear model of reflectance. Four multispectral methods were tested using data from a real trichromatic camera system. The new method gave the lowest maximum colorimetric error in terms of camera characterization with test data that were independent of the training data. However, the average colorimetric performances of the four multispectral methods were statistically indistinguishable from each other but were significantly worse than conventional methods for camera characterization such as polynomial transforms.

Quantitative assessment of commercial filter 'aids' for red-green colour defectives

The claims made for 43 commercial filter ‘aids’, that they improve the colour discrimination of red‐green colour defectives, are assessed for protanomaly and deuteranomaly by changes in the colour spacing of traffic signals (European Standard EN 1836:2005) and of the Farnsworth D15 test. Spectral transmittances of the ‘aids’ are measured and tristimulus values with and without ‘aids’ are computed using cone fundamentals and the spectral power distributions of either the D15 chips illuminated by CIE Illuminant C or of traffic signals. Chromaticities (l,s) are presented in cone excitation diagrams for protanomaly and deuteranomaly in terms of the relative excitation of their long (L), medium (M) and short (S) wavelength‐sensitive cones. After correcting for non‐uniform colour spacing in these diagrams, standard deviations parallel to the l and s axes are computed and enhancement factors El and Es are derived as the ratio of ‘aided’ to ‘unaided’ standard deviations. Values of El for traffic signals with most ‘aids’ are <1 and many do not meet the European signal detection standard. A few ‘aids’ have expansive El factors but with inadequate utility: the largest being 1.2 for traffic signals and 1.3 for the D15 colours. Analyses, replicated for 19 ‘aids’ from one manufacturer using 658 Munsell colours inside the D15 locus, yield El factors within 1% of those found for the 16 D15 colours.

Evaluation of a model to predict anomalous-observer performance with the 100-hue test

Two subjects, protanomalous and deuteranomalous, performed the Farnsworth-Munsell 100-hue test with and without prescribed ColorView spectacle aids under simulated D65 lighting. Errors were greater with aids than without. Using spectral measurements of test reflectance, aid transmittance and lighting, chromaticities of the 100-hue caps were calculated with and without aids in the uniform chromaticity diagrams for protanomaly and protanomaly [Ophthalmol. Physiol. Opt.30, 685 (2010).]. Errors were modeled from chromatic spacing on a smoothed 100-hue locus together with a distractor term, derived from the distances of raw data from that locus. Good correspondence was found between the measured test and model profiles for the major maxima as well as other aspects of shape and position.

Knitted fabric effects using two-coloured (marl) yarns

Marl yarn, which is regularly used in knitwear and contributes to the scope of knitted fabrics, is often used in response to the colour effects that this yarn can offer the designer. Whilst there is relatively little understanding of the formation of such colour effects, this paper summarises a study on a marl yarn knitting technique to move the level of understanding forward. In this study, four elements: yarn type, yarn colours, knitting machine gauge, and knitting structure have each been considered within the knitting process. A set of 72 samples were knitted by combining different elements systematically. A new terminology ‘marledness’ has been defined and is referred to as: two plied or twisted yarns of different colours to form a knitted sample with colour effects that are evenly distributed in a dotted manner. If the yarns are not twisted together before knitting and tension variations occur, then the result can be a barred effect. Based on the criterion of ‘marledness’, 10 experts and 10 inexperienced observers were asked to rank the outcomes in order. These results allow for a better understanding on how to prepare the yarns and knitting process to achieve different degrees of marledness.