Appendices - Feature Extraction and Image Processing - page 320

Processed

0 1 2 3 4 5 6 7 8 9

0 148 150 166 196 196 185 185 172 148 168

1 172 166 176 196 179 185 185 148 148 172

2 176 185 185 192 192 196 150 150 150 176

3 176 182 185 196 196 185 148 146 150 176

4 176 185 185 192 190 173 150 148 172 176

(b)

brighter = 5 185 185 185 196 188 166 148 174 172 184

6 186 185 180 190 173 148 168 185 185 185

7 185 179 196 192 166 148 176 176 185 185

Original

8 173 184 202 179 148 164 176 186 185 179

9 150 185 196 166 148 148 174 188 179 176

10 168 192 190 166 148 148 180 188 179 151

11 174 188 173 166 166 146 172 176 179 176

12 174 184 166 150 148 148 150 150 168 168

(c)

(a)

400

b_ey e_hist bright

200

0 0

100 200

Bright

Which is what we expect; it's just been moved along the brightness axis (it now starts
well after 100), and reveals some detail in the histogram which was obscured earlier.
Generally, for point operators we generate a function which is used as a look-up table
to find the new value of a point. Pure scaling is a look-up table whose graph is a straight
line with offset set by the level. The slope of this line can be:

(i) positive and >1 for magnification;
(ii) positive and <1 for reduction;

and (iii) negative ( + constant) for inversion.