David R. Wyble

A critical review of spectral models applied to binary color printing

A critical review of binary color printing models is presented. The goal is to provide an understanding of the application of color printer models as a component for device profiles within a color management system. A short description of a modern color management system is pre- sented, followed by a brief explanation of the halftoning process. This leads into the discussion of the individual models, which takes an historical approach. The discussion starts with early models proposed in the 1930s by Murray, followed by Neugebauer, Yule and Nielsen, and other much more recent model forms. To aid in gathering the appro- priate data for printer modeling, experimental techniques are then discussed, followed by an explanation of the model optimization methods needed for parameter fitting. The re- view concludes with procedures for model evaluation and a presentation of the results from an application of the models to a sample dataset for an electrophotographic printer.

Prediction of Munsell Appearance Scales Using Various Color-Appearance Models

The chromaticities of the Munsell Renotation Dataset were applied to eight color-appearance models. Models used were: CIELAB, Hunt, Nayatani, RLAB, LLAB, CIECAM97s, ZLAB, and IPT. Models were used to predict three appearance correlates of lightness, chroma, and hue. Model output of these appearance correlates were evaluated for their uniformity, in light of the constant perceptual nature of the Munsell Renotation data. Some background is provided on the experimental derivation of the Renotation Data, including the specific tasks performed by observers to evaluate a sample hue leaf for chroma uniformity. No particular model excelled at all metrics. In general, as might be expected, models derived from the Munsell System performed well. However, this was not universally the case, and some results, such as hue spacing and linearity, show interesting similarities between all models regardless of their derivation.

Matching image color from different cameras

Can images from professional digital SLR cameras be made equivalent in color using simple colorimetric characterization? Two cameras were characterized, these characterizations were implemented on a variety of images, and the results were evaluated both colorimetrically and psychophysically. A Nikon D2x and a Canon 5D were used. The colorimetric analyses indicated that accurate reproductions were obtained. The median CIELAB color differences between the measured ColorChecker SG and the reproduced image were 4.0 and 6.1 for the Canon (chart and spectral respectively) and 5.9 and 6.9 for the Nikon. The median differences between cameras were 2.8 and 3.4 for the chart and spectral characterizations, near the expected threshold for reliable image difference perception. Eight scenes were evaluated psychophysically in three forced-choice experiments in which a reference image from one of the cameras was shown to observers in comparison with a pair of images, one from each camera. The three experiments were (1) a comparison of the two cameras with the chart-based characterizations, (2) a comparison with the spectral characterizations, and (3) a comparison of chart vs. spectral characterization within and across cameras. The results for the three experiments are 64%, 64%, and 55% correct respectively. Careful and simple colorimetric characterization of digital SLR cameras can result in visually equivalent color reproduction.

Analysis of spectrophotometer specular performance using goniometric information

The 1986 CIE document 15.2, Colorimetry, was necessarily broad in specifying the use of the gloss trap or specular port in integrating sphere measurements. This has led to a variety of spectrophotometer configurations that adhere to the CIE recommendation. To help uses of these devices determine the performance of their instruments with respect to specular excluded measurements, a procedure has been demonstrated to quantify the effective specular port width of an integrating sphere device. The proposed procedure has been tested on four spectrophotometers, three of which use conventional specular ports of varying sizes. The specular ports of these three devices can be physically measured, however the fourth device uses and alternative method for the specular excluded measurement, and the diameter of its specular port cannot simply be measured. The procedure allows for a relative comparison of conventional devices and those using an alternative method.