Image Filtering

Problem!

• Noise is a problem, even in images!

Gaussian Noise Salt and Pepper Noise

What to do?

• Try to think of ways to remove the noise!

Gaussian Noise Salt and Pepper Noise

Smoothing

• The most obvious and easy way to remove the noise is by averaging.

• We can average pixels of a specific neighborhood by convolution with an averaging filter.

Smoothing

• Convolution is a simple mathematical operation.

Smoothing

• Smoothing using 3x3 mean filter.

Gaussian Noise Salt and Pepper Noise

Gaussian Filter

• Gaussian filter is more natural!

Gaussian Filter

• Gaussian mask with σ=1.

Gaussian Filter

• Gaussian filter is more natural!

Gaussian Noise Gaussian 5x5 Filter

Median Filter

• Median filter operation.

Median Filter

• Removing Salt and Pepper Noise using Median Filtering.

Salt and Pepper Noise 3x3 Median Filter

Edge Detection

• Finding the edges of images is a very useful tool.

• How do we find the edges in images?

Edge Detection

• Yes you’re right, derivatives!!

Edge Detection

• We use image filtering to find edges.• There are many masks: Prewitt, Sobel, Roberts

Roberts

Sobel

Prewitt

Edge Detection

• The gradient magnitude and gradient angle can be calculated as follows: