Influence of Luminance L* in the L*a*b* Color Space during Color Segmentation in Highly Saturated Color Images

In this paper a study of the influence of luminance L* at the CIE L* a* b* color space during color segmentation in highly saturated color images is presented. A comparative study is made between the behavior of segmentation in color images using (1) the Euclidean metric of the RGB channels (2) the Euclidean metric of a* and b* in CIE L*a*b* color space and (3) an adaptive color similarity function defined as a product of Gaussian functions in a modified HSI color space. For the evaluation, synthetic images were particularly designed to accurately assess the performance of the color segmentation. The testing system can be used either to explore the behavior of a similarity function (or metric) in different color spaces or to explore different metrics (or similarity functions) in the same color space. From the results it was obtained that the color parameters a* and b* are not independent of the luminance parameter L* as one might initially assume. In the majority of cases the CIE L*a*b color space was more influenced by the faded shadow than the RGB color space. The segmentation using the Euclidean metric in L*a*b* color space suffered errors in all cases. It manifested in different degrees and at different levels of faded shadow (less than 10% to 80%).