Histogram equation & quantization:

Image Processing - Performing intensity transformations: histogram equalization, and optimal quantization

some exemples:

histogram equalization:

gray image:

before equalization:

after equalization:

RGB image:

before equalization:

after equalization:

optimal quantization:

gray image:

before quantization: 🐒

after quantization to 4 intensities:

after quantization to 2 intensities:

RGB image:

before quantization:

after quantization to 10 intensities:

after quantization to 4 intensities:

after quantization to 2 intensities: