Chapter 4

Question 1

What is point processing?

Answer 1

Calculates value of pixel in output image based on the same posiotioned pixel in the original image. (f(x,y) - g(x,y))

Question 2

What is grey level mapping?

Answer 2

Output pixel is equal to input pixel plus a constant (g(x,y) = f(x,y) + b)

Question 3

What is grey level contrast?

Answer 3

difference in pixel values

Question 4

How to change grey level contrast?

Answer 4

g(x,y) = a * f(x,y)

Question 5

How to combine brightness and contrast adjustment:

Answer 5

G(x,y) = a*f(x,y) + b - this is a straight line.

Question 6

How to perform an optimal brightness and contrast change

Answer 6

see notes

Question 7

What can we use a image histogram for?

Answer 7

Investigating the gray-level/colour ranges expressed in the picture.

Question 8

What is histogram stretching?

Answer 8

Making sure that an image histogram ranges from 0 to 255 (grey level) done by:

g(x,y) = 255/(f_high - f_low) * (f(x,y)-f_low)

Question 9

Problems with histogram stretching?

Answer 9

Vulnerable to outliers - histogram equalization can be done instead.

Question 10

What is gamma-mapping?

Answer 10

g(x,y) = f(x,y) ^ gamma - more dynamic in certain regions

Question 11

What is log mapping?

Answer 11

g(x,y) = c*log(1+f(x,y))

c =255/Log(1+f_max)

Good for enhancing low pixel values.

Question 12

What is thresholding?

Answer 12

Everything on either side of a threshold either dark or light.

Question 13

Prerequisites for thresholding:

Answer 13

Bimodal histogram

Question 14

Otzu’s method:

Answer 14

does automatic thresholding into 2 classes by minimizing combined class variance.