**5.2 Enhancement of visual images**

The ETNUD algorithm was applied to 16 visual images as shown in Figure 6 under different illumination conditions. In all figures besides the regular room lights, the four extra spot lights located in the front of the person were turned off and on for creating different illumination conditions. To enhance those visual images, the luminance is first balanced, then image contrast is enhanced and finally, the enhanced image is obtained by a linear color restoration based on chromatic information contained in the original image. The results in the luminance enhancement part showed that the algorithms work well for dark images. All the details, which cannot be seen in the original image, become evident. The experiment results have shown that for all color images, the proposed algorithms work sufficiently well.
