CP467 - Intensity transformation and Histogram Processing

Two types of image enhancement?

1. Spatial domain methods (The image plane itself)
2. Frequency domain methods (Based on Fourier transform)

Formula for spatial domain process

g(x,y) = T[f(x,y)]

T is an operator on f, defined over neighbourhood of (x,y)

What are the 4 types of point operations?

1. Image negatives
2. Log transformations
3. Power-law transformations
4. Piecewise-linear transformation functions

What are image negatives?

The negative of an image with grey levels in the range [0,L-1] obtained by s = L - 1 - r

What are log transitions? What's the general formula?

Transformation maps a narrow range of low gray-level values in the input image into a much wider range of output levels.

General formula: s = c log (1 + r)

What is the basic form of the power-law transformations?

s = cr^y

What are the 3 types of functions for piecewise-linear transformations?

1. Contrast stretching
2. Gray-level slicing
3. Bit-plane slicing

What is the principal advantage of piecewise-linear transformations?

Form of piecewise functions can be arbitrarily complex

What is the principal disadvantage of piecewise-linear transformations?

Their specifications requires considerably more user input

Purpose of contrast stretching?

To increase the dynamic range of the gray levels

Purpose of gray-level slicing?

Used for highlighting a specific range of gray levels in an image

Purpose of bit-plane slicing?

Highlights the contributions made to total image appearance by specific bits. Useful for image compression

Formula for histogram normalization

p(rk) = nk/MN (k is subscripted)
- Where MN is the number of pixels in the image M rows N columns

What is histogram equalization?

A technique to enhance image contrast by spreading out the intensity levels evenly across the histogram

What is the cumulative distribution function?

The mapping of a continuous or discrete random variable with the cumulative probability of occurrence

What is histogram matching?

The method used to generate a processed image that has a specified histogram