topic 5 - image noise

Question 1

what is image noise? (correlated noise)

Answer 1

Correlated noise

Halftone distortion / moiré patterns

Due to electrical interference

Due to source / sensor interference.

Question 2

what is image noise? (uncorrelated noise)

Answer 2

Uncorrelated noise

Shot noise & thermal noise in sensor

Silver halide grains in film photography

Neuronal noise in a retina

Quantization noise in digital photographs.

Question 3

how do you remove noise with an averaging filter?

Answer 3

The result is actually no better. There’s less noise but the blurring looks worse.

Question 4

how do you remove salt and pepper noise with a median filter?

Answer 4

Returns the median value of the pixels in a neighborhood

Is non-linear

Is similar to a uniform blurring filter which returns the mean value of the pixels in a neighborhood of a pixel

Unlike a mean value filter the median tends to preserve step edges.