1 Effects of Texture on Colour Appearance David P. Oulton 1 *, Elise Peterman 2 , and Andrew W. Bowen 1 . 1 Dept of Textiles, UMIST, Manchester, M 60 1QD, U.K 2 Oxley Thread, Ashton-u-Lyne, Manchester. *Correspondance to Mr. David P. Oulton, Dept of Textiles, UMIST, Manchester, M 60 1QD, U.K. Introduction This paper reports on part of a comprehensive EPSRC funded investigation [1] into colour and texture. The project aimed to establish as separate variables of colour appearance, a model of colorant formulations, and a model of the colour appearance of that formulation when applied to a given texture. The models are validated using a visual simulation of colour appearance on a computer screen that has been accurately calibrated [2,3,4] , so that individual pixel colour can be controlled and reproduced to within an average E 0.5 CMC(2:1) D 65 CIE 10 o Observer colour difference [5] . Photo-realistic images of a wide range of textures have been captured [6] . They focused on materials such as lace and sewing thread, multi-coloured melange yarns, and lustrous crepe fabric. The detailed colour differences between each point making up the surface texture have been recorded at a resolution of approximately 100 microns [7] . The definition of surface colour appearance produced, consists of many thousand CIE co-ordinate colour definitions arranged in a two-dimensional array of pixels, which combine to give a realistic simulation of a coloured textured surface. The additive properties of Tristimulus values [8] are invoked, to model the relationship between variations in colour appearance due to texture, and the intrinsic colour represented by a colorant formulation. The paper seeks to establish quantifiable relationships between intrinsic colour and texture as distinct contributing variables of colour appearance. The results of visual matching experiments are the basis for colorimetric modeling, and have been used to define the psychophysical attributes of the human sensation of colour [8,9,10,11] . They define on one hand colour identity, and on the other the modification of colour identity by factors external to the interaction of colorants with light. Human observers are naturally skilled at judging when dissimilar textures are an acceptable match in colour appearance. In this investigation visual matching techniques have been combined with colorimetric analysis of matched images; in order to quantify colour appearance differences. Both the colorimetric accuracy of the data derived from images, and the accuracy of the matching process itself is assessed. Surface texture effects are responsible for substantial visual colour shifts. Industrial colorant formulation only works well, if texture, measurement, and observation conditions are all held constant, and reflectance curve colour definitions generated