A Computational Introduction to Digital Image Processing, 2nd Edition

Point Processing 77

FIGURE 4.16: The function used in Figure 4.15

A Piecewise Linear Stretching Function

We can easily write our own function to perform piecewise linear stretching as shown in

Figure 4.17. This is easily implemented by first specifying the points (a

i

, b

i

) involved and

a

1

a

2

a

3

a

4

b

1

b

2

b

3

b

4

FIGURE 4.17: A piecewise linear stretching function

then using the one-dimensional interpolation function

interp1 to join them. In this case,

we might have:

MATLAB/Octave

>> a = [0 100 150 255]

>> b = [40 100 220 255]

>> lin = interp1(a,b,0:255,’linear’);

Then it can be applied to the image with

MATLAB/Octave

>> cl = uint8(lin(c+1));

Python also provides easy