Invariance

Question 1

List the 5 types of invariance

Answer 1

Illumination
Scale
Rotation
Affine
Full Perspective

Question 2

How do you achieve illumination invariance?

Answer 2

Normalise the image to the highest intensity value in the image

Question 3

What is the pyramid method for scale invariance?

Answer 3

Take an image and apply your feature detection. Reduce the images height and width by 50% and apply the same feature detection. Repeat this. If the feature appears in all images it is a scale invariant feature.

Question 4

What is the difference of gaussian method of scale invariance?

Answer 4

Like pyramid, but apply several Gaussian filters to each image. Keep the features that appear in all of the filtered images.

Question 5

How do you achieve rotation invariance?

Answer 5

Make a histogram of all gradient directions. Rotate all images to the most dominant one.