Image Processing Reference

In-Depth Information

Fig. 4.11
The histograms of a color image

Fig. 4.12
The concept of histogram stretching

We obtain this by mapping the left-most non-zero bin in the histogram to 0 and the

right-most non-zero bin to 255, see Fig.
4.12
.

We can see that the histogram has been stretched so that the very dark and very

bright values are now used. It should also be noted that the distance between the

different bins is increased, hence the contrast is improved. This operation is denoted

histogram stretching
and the algorithm is exactly the same as Eq.
4.3
with
a
and
b

defined as in Eq.
4.4
.
f
1
is the left-most non-zero bin in the histogram and
f
2
is the

right-most non-zero bin in the histogram of the input image.