Colour normalization of fundus images based on geometric transformations applied to their chromatic histogram
The high variability in fundus image databases is an important limiting drawback for detecting some retinal pathologies automatically. Age, human retinal pigmentation or lighting conditions affects in the colour of the acquired images. In this paper a colour-normalization method is presented as an initial pre-processing step in order to reduce the heterogeneity of retinal databases. The proposed method is based on geometric transformations applied to the chromaticity diagram of a target image taking into account a reference image. With the aim of quantifying the effect of the proposed colour normalization, a bright lesion detection from pathological images is carried out. A home-made system based on texture analysis and Support Vector Machine classification is used for this purpose. An improvement around a three percent in the detection accuracy demonstrates the importance of a retinal image colour pre-processing before any specific analysis.