How Itten's color diagram fails to illustrate color mixing of paints.

Itten's color diagram, published in 1961, is still considered by many to be the cornerstone of color education. We show experimentally and theoretically that by mixing oil paints it is hardly possible to reproduce Itten's primary colors red, yellow and blue such that their mixtures produce Itten's secondary colors orange, green and purple. Optical models show why it is highly unlikely that paints can be created that follow the color mixing rules from Itten's color diagram.

Accurate physics-based digital reproduction of effect coatings.

We built an improved 3D rendering framework to accurately visualize the complete appearance of effect coatings, including metallic effects, sparkle and iridescence. Spectral reflectance measurements and sparkle indexes from a commercially available multi-angle spectrophotometer (BYKmac-i) were used together with physics-based approaches, such as flake-based reflectance models, to implement efficiently the appearance reproduction from a small number of bidirectional measurement geometries. With this rendering framework, we rendered a series of effect coating samples on an iPad display, simulating how these samples would be viewed inside a Byko-spectra effect light booth.

Visual validation of the appearance of chromatic objects rendered from spectrophotometric measurements.

We validate a physically based and spectral rendering framework with improved color reproduction. With a recently developed model, we take into account both the colorimetric specifications of the rendering display as well as the spectral and angular characteristics of lighting and also the spectral reflectance of the objects. Therefore, it should provide much better color reproduction than those based on the common standard red, green, blue (sRGB) color space.

Predicting the performance of low-cost color instruments for color identification.

During the past few years, several instruments for color measurement have become commercially available at unprecedented low prices. Although these instruments are no spectrophotometers, their price-performance ratio may be attractive for applications that do not require the high accuracy of traditional instruments. We investigated the performance of this class of instruments.

Improving Color Accuracy of Colorimetric Sensors.

Accurate measurements of reflectance and color require spectrophotometers with prices often exceeding $3000. Recently, new “color instruments” became available with much lower prices, thanks to the availability of inexpensive colorimetric sensors. We investigated the Node+ChromaPro and the Color Muse, launched in 2015 and 2016 by Variable Inc.

Improving color reproduction accuracy of a mobile liquid crystal display.

The default method for color representation on displays involves sRGB as device-independent encoding color space. For improving color reproduction accuracy, we develop a device-specific display characterization model for the Apple iPad Air 2. In separate articles, we will evaluate the same method for other devices and for other display technologies.

How color difference formulas depend on reference pairs in the underlying constant stimuli experiment.

For calculating color differences, the CIEDE2000 and CIE94 equations are widely used and recommended. These equations were derived more than a decade ago, based for a large part on the RIT-Dupont set of visual data. This data was collected from a series of psychophysical tests that use the method of constant stimuli.

Visibility of sparkle in metallic paints.

For suitable illumination and observation conditions, sparkles may be observed in metallic coatings. The visibility of these sparkles depends critically on their intensity, and on the paint medium surrounding the metallic flakes. Based on previous perception studies from other disciplines, we derive equations for the threshold for sparkles to be visible.

How psychophysical methods influence optimizations of color difference formulas.

For developing color difference formulas, there are several choices to be made on the psychophysical method used for gathering visual (observer) data. We tested three different psychophysical methods: gray scales, constant stimuli, and two-alternative forced choice (2AFC). Our results show that when using gray scales or constant stimuli, assessments of color differences are biased toward lightness differences.

Isochromatic lines as extension of Helmholtz reciprocity principle for effect paints.

Flake-based parameters were recently introduced as a physical concept to predict a series of measurement geometries producing similar reflection data for effect paints. We derive expressions to calculate these so-called isochromatic lines, connecting the two Helmholtz-reciprocal in-plane geometries with a series of out-of-plane geometries. Thus isochromatic lines can be regarded as an extension of the Helmholtz reciprocity principle, which is valid for effect paints.