Digital images and point processing

Question 1

Spatial sampling

Answer 1

Clear picture:
Spatially continuous light intensity function
Projection onto discrete sensor array

Blurry picture:
Spatially discrete light intensity function
Sensor photosites register average colour

Question 2

Digital image formation - greyscale and colour

Answer 2

Colour images have 3 values per pixel, monochrome images have 1 value per pixel

A digital image is a grid of squares, each of which contains a single colour
Each square is called a pixel

Question 3

Human visual system

Answer 3

The human eye has 3 types of cone photoreceptors: sensitive to red, green or blue light

The brain transforms RGB into seperate brightness and colour channels

Question 4

Point Processing

Answer 4

The term point refers to pixel
Point processing adjusts a pixels value according to a transformation function usually for the purpose of improving the perceived image quality
The transformation is independent of the values of the neighbouring pixels

Question 5

Point processing - typical adjustments

Answer 5

Brightness and constant adjustment
Gamma correction
Histogram equalization
Colour correction

To determine quality of an image we must consider its histogram. The histogram just records the number of pixels within an image at each light intensity value and is displayed as a bar chart

Question 6

Histograms

Answer 6

There is one histogram per colour band

Question 7

LUT - look up table

Answer 7

An LUT implements a functional mapping of pixel intensity values
To remap the intensity values of an output image I, to the output image , J