07-05-2014, 03:07 PM
Digital Image Processing
What Is Image Enhancement?
Image enhancement is the process of making images more useful
The reasons for doing this include:
Highlighting interesting detail in images
Removing noise from images
Making images more visually appealing
Spatial & Frequency Domains
There are two broad categories of image enhancement techniques
Spatial domain techniques
Direct manipulation of image pixels
Point processing
Histogram processing
Neighbourhood operations
Frequency domain techniques
Manipulation of Fourier transform or wavelet transform of an image
For the moment we will concentrate on techniques that operate in the spatial domain
Point Processing
In this lecture we will look at image enhancement point processing techniques:
Negative images
Thresholding
Logarithmic transformation
Power law transforms
Grey level slicing
Bit plane slicing
Logic operations
Image subtraction
Image averaging
Gamma Correction
Prior Knowledge about gamma correction
Varying the value of gamma correction changes not only the brightness, but also the ratio of red to green to blue.
Applications
Internet
Millions of people and millions of monitors
Gamma represents an “average ”of the types of monitors and computer systems
Scanners, Printers have different values of gamma
Summary
We have looked at different kinds of point processing image enhancement
Next time we will start to look at:
Histogram processing
Neighbourhood operations – in particular filtering and convolution