Tutorial Images

Clifford Watson,
Department of Applied Mathematics,
University of Washington,
Seattle, Washington 98195

This is a demo showing different image processing techniques.

Here is the ORIGINAL image, taken from the photo "Robin Jeffers at Ton House" (1927) by Edward Weston. [Weston]

SAMPLING RATE

Here is the image with every 3rd pixel sampled, and the intermediate pixels filled in with the sampled values.

Note the blocky appearance of the new image.

QUANTIZATION

Here is the image with only 5 greyscale shades; the original has 184 shades.

Note how much detail is retained with only 5 shades!

LOW PASS FILTERING

Here is the image filtered with the following kernel:

                     1/9 1/9 1/9
                     1/9 1/9 1/9
                     1/9 1/9 1/9

This filter is a 3-by-3 mean filter - notice how it smooths the texture of the image while blurring out the edges.

LOW PASS FILTERING II

Here is the image filtered with the following 5-by-5 mean kernel:

                     1/25 1/25 1/25 1/25 1/25
                     1/25 1/25 1/25 1/25 1/25
                     1/25 1/25 1/25 1/25 1/25
                     1/25 1/25 1/25 1/25 1/25
                     1/25 1/25 1/25 1/25 1/25

Notice the difference between the images from the two filters?

EDGE DETECTION

Here is the image filtered with the following kernel:

                     0 -1  0
                    -1  4 -1
                     0 -1  0

This filter is a 2-dimensional Laplacian (actually the negative of the Laplacian) - notice how it brings out the edges in the image.

EDGE DETECTION II

Top right: Here is the image filtered with the following kernel:


      0 -1  0     0 0 0         0 -1  0
     -1  4 -1  +  0 1 0    =   -1  5 -1
      0 -1  0     0 0 0         0 -1  0

This is the Laplacian filter with the original image added back in - notice how it brings out the edges in the image while maintaining the underlying greyscale information.