RESEARCH ON ILLUMINATION INVARIANCE COLOUR INDEX ALGORITHM BASED ON COLOUR RATIO
Fei Cai1, 2, 3, Wenjun Wang1, 2
1School of Computer Science and Technology, Tianjin University, Tianjin 300072, China
2Tianjin Key Laboratory of Cognitive Computing and Application, Tianjin 300072, China
3School of Civil Engineering, Shandong Jianzhu University, Jinan, 250101, China
Statistics of colour value of each pixel in the image are output in traditional colour histograms. Therefore, though the two same images photographed in different illuminations are consistent in colour content, they have different colour distributions in the histograms. To solve the problem, this paper introduces an illumination invariance colour index algorithm based on colour ratio. According to the colour constancy theory, although colour values of its pixels will be changed once the image is subject to illumination, colour ratios remain unchanged. Colour ratio refers to the ratio between two contiguous pixels. As per colour ratios, colour ratio image may be obtained, which depicts obvious boundaries or margins of the image content so that we statistics of colour ratio histogram can be obtained as an index mechanism to remove illumination effect. Verified by lots of tests, this method can extract useful colour characteristics and remove illumination effect, so that it can be practically used in effective computer recognition of objects in traffic videos.