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