Search

Featured Application: To compute total spectral irradiance on the surface of Mars from a selected value of correlated color temperature in the range of 2333 K–5868 K. We analyzed the main colorimetric characteristics of lights on Mars' surface from 3139 total spectral irradiances provided by the COMIMART model (J. Space Weather Space Clim. 5, A33, 2015), modifying the parameters of 'solar zenith angle' and 'opacity', related to the time of day and the amount of dust in the atmosphere of Mars, respectively. Lights on Mars' surface have chromaticities that are mainly located below the Planckian locus, correlated color temperature in the range of 2333 K–5868 K, and CIE 2017 color fidelity indices above 93. For the 24 samples in the X-Rite ColorChecker® and an extreme dust opacity change from 0.1 to 8.1 in the atmosphere, the average color inconstancy generated by the change in Mars' light using the chromatic adaptation transform CIECAT16 was about 5 and 8 CIELAB units for solar zenith angles of 0° and 72°, respectively. We propose a method to compute total spectral irradiances on the surface of Mars from a selected value of correlated color temperature in the range of 2333 K–5868 K. This method is analogous to the one currently adopted by the International Commission on Illumination to compute daylight illuminants on the surface of Earth (CIE 015:2018, clause 4.1.2). The average accuracy of 3139 reconstructed total spectral irradiances using the proposed method was 0.9999558 using GFC (J. Opt. Soc. Am. A 14, 1007–1014, 1997) and 0.0009 ΔEu′v′ units, a value just below noticeable chromaticity differences perceptible by human observers at 50% probability. Total spectral irradiances proposed by Barnes for five correlated temperatures agreed with those obtained from the current proposed method: on the average, GFC = 0.9979521 and 0.0023 ΔE′v′ units. [ABSTRACT FROM AUTHOR]

We analyzed the main colorimetric characteristics of lights on Mars’ surface from 3139 total spectral irradiances provided by the COMIMART model (J. Space Weather Space Clim. 5, A33, 2015), modifying the parameters of ‘solar zenith angle’ and ‘opacity’, related to the time of day and the amount of dust in the atmosphere of Mars, respectively. Lights on Mars’ surface have chromaticities that are mainly located below the Planckian locus, correlated color temperature in the range of 2333 K–5868 K, and CIE 2017 color fidelity indices above 93. For the 24 samples in the X-Rite ColorChecker® and an extreme dust opacity change from 0.1 to 8.1 in the atmosphere, the average color inconstancy generated by the change in Mars’ light using the chromatic adaptation transform CIECAT16 was about 5 and 8 CIELAB units for solar zenith angles of 0° and 72°, respectively. We propose a method to compute total spectral irradiances on the surface of Mars from a selected value of correlated color temperature in the range of 2333 K–5868 K. This method is analogous to the one currently adopted by the International Commission on Illumination to compute daylight illuminants on the surface of Earth (CIE 015:2018, clause 4.1.2). The average accuracy of 3139 reconstructed total spectral irradiances using the proposed method was 0.9999558 using GFC (J. Opt. Soc. Am. A 14, 1007–1014, 1997) and 0.0009 ΔEu′v′ units, a value just below noticeable chromaticity differences perceptible by human observers at 50% probability. Total spectral irradiances proposed by Barnes for five correlated temperatures agreed with those obtained from the current proposed method: on the average, GFC = 0.9979521 and 0.0023 ΔE′v′ units.

Color constancy is something we take for granted. An apple appears red despite monumental changes in the intensity and spectral balance of illumination. There are many components to the human visual system that make this illusion possible. Nonetheless, the system is imperfect. Objects will change apparent color under different illumination. The CIELAB color space allows for the computation of color values under any illuminant. CIELAB values will, in general, change as the illuminant changes. It would be natural to assume that these changes in CIELAB values would agree with the apparent color change that a human would experience. But the chromatic adaptation built into CIELAB is known to be less than optimal due to an imperfect emulation of how the adaptation process is performed in the human visual system. As a result, at least part of the illuminant color change implied by the CIELAB values is an artifact of this imperfect emulation. This paper investigates the magnitude of this artifact by comparing color changes implied by CIELAB with color changes in a color system that mimics CIELAB, except that it more closely emulates the human visual system. The difference between the two estimates of color change is assumed to be an artifact of CIELAB's poor emulation of the chromatic adaptation process. As color manufacturers are dealing with a wider spectrum of illumination sources, they may wish to consider the issue of color constancy; what colors and what formulations of colors exhibit better color constancy? Can CIELAB be used to quantify this? Or are color spaces that are based on LMS rather than XYZ more appropriate? [ABSTRACT FROM AUTHOR]

Metamerism is a critical color phenomenon which can cause serious problems for products assembled by various parts. Customers generally expect all parts are color‐matched under different observing conditions. This article extends the concepts of illuminant and observer metamerism to observing‐condition metamerism, that is, objects are color‐matched under one observing condition but not under others. The color inconstancy of a single object is also expanded to be evaluated under multiple observing conditions. Moreover, four Waypoint (Wpt) Shift Manifold difference metrics are proposed to evaluate not only observing‐condition metamerism of metamers and paramers but also observing‐condition color inconstancy of single objects: The Mean Object Inconstancy Index (MOII), The Mean Object Color Difference (MMOCD), Object Metamer Index (OMI), and Object Hue Similarity Index (OHSI). Existing indices of metamerism and color inconstancy employ appearance matching using a Chromatic Adaptation Transform (CAT) and color difference formulas such as CIEDE76 or CIEDE2000. The proposed metrics utilize material matching based upon the Waypoint Material Adjustment Transform (Wpt‐MAT) and Euclidian color difference in the perceptually uniform Material Color Equivalency Space WLab. Conceptual comparisons between these approaches are discussed and evaluated. Additionally, computational evaluation results under observing conditions composed by 99 illuminants and 70 observers show that MOII provides a measure of color inconstancy for single objects, MMOCD provides a measure of metamerism between metamers and paramers with a generalized assessment of color difference between two objects, OMI provides a measure of paramers, and OHSI provides a quantitative measure of hue characteristics for different observing conditions. [ABSTRACT FROM AUTHOR]

The main goals of this research are investigation and determination of color balance failure (color inconstancy) of offset printed images expressed by color difference depending on the material used and different standard illuminant conditions. For the experiment, we chose three of the most commonly used in practice illuminants -- CIE D50 natural horizon daylight with color temperature 5003 K; CIE F2 cool white fluorescent, 4230 K; CIE A typical Tungsten-filament lighting, 2856 K. A special test form that has been used contains different control strips and measurement components include test chart TC6.02 with about 1000 color patches with different percent combinations of cyan, magenta, yellow and black. The paper, printing inks and printing presses employed in the experiment are some of most commonly used in practice for producing high quality color reproductions. A series of colorimetric and densitometric measurements were performed for different combinations of C, M, Y, K in single, double, triple and quadruple overprint for high tones, middle tones and dark tones. For estimating color balance failure for all the above mentioned measurements there have been calculated the color difference ΔEab* and CMCCON02 depending on standard illuminants CIE D50, F2 and A. For the first time via experimental research in real production conditions (for offset printing method), 3D and 2D presentations and comparison of color gamuts and color gamut volumes for different illuminants were made. According to the results, CIE A has the biggest color gamut volume and CIE F2 -- the smallest one. The results obtained are important from scientific and practical points of view. For the first time a methodology is suggested and implemented for examination and estimation of color shifts by studying a big number of color changes in various ink combinations for different illuminants. [ABSTRACT FROM AUTHOR]