On the edge: A scalable daltonization method focusing chromatic edges and contrast

Joschua Simon-Liedtke,Ivar Farup,Reiner Eschbach

doi:10.2352/issn.2470-1173.2017.18.color-030

Abstract

Color Vision Deficiency (CVD) leads to a reduced capability to identify chromatic edges and contrast and may cause significant problems in various color tasks like, for example, comparative color tasks. Many daltonization methods to improve color perception of color-deficient people, however, change naturalness of confusion colors, which might complicate other color tasks like, for example, connotative and denotative color tasks. Thus, we present a daltonization method focusing on the enhancement of chromatic edges and contrast while preserving the naturalness of object colors as good as possible. Our proposed method, Yoshi-II-edge, is based on a previously presented method, Yoshi-II, which projects and rotates the lost information by color-deficient observers along the direction of optimal visibility. Yoshi-II-edge limits this enhancement to chromatic edges and contrast by computing an edge map obtained from the gradient of the error image between the original and its simulation. Furthermore, we propose a threshold and dilation to influence the width of the daltonized edge. We show that the performance of this method depends on the juxtaposition of confusion colors in the image. More precisely, Yoshi-II-edge performs well in images with adjacent areas of confusion colors but performs poorly in images with non-adjacent areas of confusion colors.

Highlights

Luminance and chromatic edges and contrast play a major role in the processing of visual information of the human visual system (HVS) [2]
We presented a spatial daltonization method based on transformations in the gradient domain and scale-space improving chromatic edges and contrast at different scales of the image
In Yoshi-II, we create a modified gradient, G, by projecting and rotating in color space the lost information between the original image and its simulation towards the direction of optimal visibility that is orthogonal to both the direction of lightness and the direction of maximum information loss: G = ∇u0 + (∇u0 · ed )(χec). In this formula, ed and ec are unit vectors representing the direction of maximum information loss and direction of optimal visibility respectively. (∇u0 · ed) represents an approximation of the lost information. χ is an spatial scalar influencing how much a confusion color is changed at any given point

Summary

Introduction

Luminance and chromatic edges and contrast play a major role in the processing of visual information of the human visual system (HVS) [2]. Color-deficient observers can be said to have a higher level of metamerism than normal-sighted observers This leads them to see two colors as identical that are distinguished by a normal-sighted observer. In YoshiII-edge, we introduce an edge map that restricts daltonization only to chromatic edges and contrasts that are difficult to perceive by color-deficient people. We propose an option for “artificial mach bands” to highlight said chromatic edges more clearly [6][pp.131]. Computations for both Yoshi-II-edge and Yoshi-II take place in the gradient domain, which is well suited to detect chromatic edges and contrast. We can solve the Euler-Lagrange equation for G resulting in a Poisson equation that can be solved numerically by gradient descent

Results

Discussion

Conclusion