Contrast: Range of darkest to lightest colors in an image.

Arithmetic operations: add, subtract, multiply and divide by scalar.

Add and subtract: make image lighter and darker. Does not affect contract.

Multiply and divide: increases or decreases contrast.

Histogram manipulations: Bar graph showing intensity versus frequency.

Histogram equalization: create uniform distribution of gray levels. Steps:

- computer histogram H(I)
- Calculate normalized sum histogram:

H_n(I) = SUM_i=0~I H(i) MAX(I)/Number of Pixels - Transform input to output using H_n(I) as your LUT.

former post is more clear.

Intensity transforms: Gamma Correction: Non-Linear transform approximating the brightness (luminance) control on a CRT (computer monitor, video or image system)

V_out = V_in ^ gamma

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