Saturation clipping in the LHS and YIQ color spaces

A common approach for color image processing is to rst transform the RGB image to a new color space (such as LHS and YIQ), do the processing, and then transform back to RGB space. In many applications, only the luminance component is processed, and the hue and saturation are preserved. However, when the processed values in the new color system are transformed back to RGB, the transformed values may lie outside the RGB cube. Some researchers clip the processed luminance values before transformation from the processing color space to RGB space. This can lead to a loss of luminance contrast because many pixels may be clipped to approximately the same luminance value. Instead of clipping the luminance, this paper investigates clipping the saturation component. The gamuts of two color coordinate systems, LHS and YIQ, are studied. The procedures for saturation clipping are presented for both systems. Experimental results of clipping saturation and luminance in histogram equalization are presented in the paper. The results show that the contrast of the processed image is much better when saturation clipping is used. The luminance of the image can utilize the full dynamic range, thereby resulting in improved contrast enhancement.