Introducing WLab—Going from Wpt (Waypoint) to a uniform material color equivalency space

Abstract

A set of invertible non-linear transforms was derived that adjusts Wpt (Waypoint) coordinates (based on Wpt normalization) to and from a perceptually more uniform coordinate system (WLab or Waypoint-Lab) than that provided by Wpt that allows for the advantageous features of Wpt to be directly applied to situations where other standard color spaces are typically used. The proposed transformations were found by optimizing for perceptual uniformity over both large and small color difference scales. The Munsell color order system was used as a representation for optimizing large-scale perceptual uniformity. Correlations with Munsell value, chroma and hue along with comparisons with CIELAB and CAM02-UCS were used to correct and assess overall large-scale uniformity. The DE* 94 color difference formula was used for optimization purposes for small-scale uniformity. A STRESS analysis was applied to compare color differences based on Euclidean WLab distances with color differences based upon DE* ab , DE* 94 , DE 00 , DIN99o, CIECAM02, and CAM02-UCS. It was found that WLab is a reasonably uniform material color equivalency space with small Euclidean WLab distances not being statistically different from DE* 94 , DE 00 , and Euclidean distances of DIN99o and CAM02-UCS under reference observing conditions.

Wpt (waypoint) shift manifold difference metrics for evaluation of varying observing‐condition (observer + illuminant) metamerism and color inconstancy

“…where the function μ w (Á) is defined by several steps to adjust lightness and chroma. The details of how to convert between Wpt and WLab is described in Derhak and Berns' paper 15 and Excel spreadsheets as well as Matlab code are downloadable. 17 The color difference between two Wpt coordinates of w i 1 ,j 1 ,k 1 and w i 2 ,j 2 ,k 2 is defined by a Euclidean difference in WLab:…”

“…Alternatively, the perceptually uniform material color equivalency space, WLab, can be employed which is derived from nonlinear adjustments of chroma and lightness of Wpt coordinates. The Euclidean differences in WLab are statistically equivalent to CIEDE2000 15 , which is one of the color difference formulas employed by existing indices of color inconstancy and metamerism.…”

Review and evaluation of color spaces for image/video compression

“…Hence, these color spaces can also be called as “MAT based color spaces.” Two color equivalency‐based spaces proposed in Refs. are shown in Table .…”

“…WLab (Waypoint Lab) is obtained from the Wpt color space by nonlinear transformations on the polar coordinates of Wpt (C pt and h pt ). 102 Unlike Wpt, WLab is a perceptually uniform color space and hence can be used in situations where other standard color spaces are applicable. Like CIE L*a*b*, L coordinate in WLab indicates lightness (luminance), while a and b components represent chrominance.…”

Method to determine the degrees of consistency in experimental datasets of perceptual color differences

“…Among many color-difference formulas currently available [1,[26][27][28][29][30], here we use just the CIEDE2000 formula, because it is the current CIE/ISO recommendation to achieve the best agreement with a Note the very similar values of color coordinates of the samples and ΔE oo color differences, while the two visual differences ΔV are very different (more than a factor of 6). FM is the degree of consistency of each of these pairs from the method described in [23]; ΔM ij1 and ΔM ij;2 are distances between couples of pairs; and I ij is the degree of inconsistency (see text).…”