As illustrated in Figure 7, in the first stage T and 
reduce and reorganize the color space. The color images are first low-pass filtered and subsampled to approximately 128 x 128 pixels. The insignificant detail is further reduced in the image by non-linear filtering. This processing is accomplished using a median filter on each of the HSV channels of the subsampled image. The non-linear median filtering in HSV space eliminates outliers and emphasizes prominent color regions while preserving boundary information and avoiding the introduction of false hues.
Figure 7: First stage of color region extraction: (1) transformation T of RGB color image I[m,n] to HSV color space, (2) quantization and (3) color median filtering. The processed color image R[m,n] has dominant color regions emphasized.