Figure 1
No effect
Figure 2
%Approximate
Output_image=Input_image-L/2;
or
output_image=slope*input_image+(-c) % Decide C as per figure
Figure 3
Divide in 3 zones and do the same as Figure 2
Figure 4
Same as figure 2, change the slope and c
See the contrast stretching or gray level transfomation topics (Golzalez Book)
