Brightness of a region is perceived by the ye that does not depend on the absolute grey level values. This is because the human eye does not respond with equal sensitivity to all visual information. Some information is visually more important than others. Information which is not visually important is called Psychovisual Redundancy. Psychovisual redundancies exist in all images and are eliminated without hampering the subjective quality of image. Simply reducing the quantization i.e. number of bits of representation, compress the image but also produces false contouring I.G.S. coding reduces the quantization but also reduces false contouring. Steps involved in I.G.S coding are:

• Lower 4-bits on the preceding modified pixel are added to the present pixel.
• The new 4MSB’s of the present pixel are taken as the I.G.S code.
• Repeat step 1 and 2 after moving on to new pixel.
• If the MSB is 1111, then add 0000 instead of the 4 LSB’s of the previous sum.

For eg: Construct the IGS code for the given grey level data set {100,110,124,124,130,110,200,210}

Solution: From the grey level values it is clear that we could require 8-bits for their representation. Let I be the first pixel. We start by adding 0000 to the 1st pixel and then follow the steps given,

This type of coding reduces false contouring which is a pitfall of the uniform quantization. It also eliminates psychovisual redundancies.