Image Processing Reference
In-Depth Information
Fig. 4.25
An example of overflow and how to handle it. The addition of the images produces
values above the range of the 8-bit image, which is handled by storing the result in a temporary
image. In this temporary image the highest value is identified, and used to scale the intensity values
down into the 8-bit range. The same approach is used for underflow. This approach also works for
images with both over- and underflow
Image arithmetic has a number of interesting usages and here two are presented.
In Chap. 8 we present another one, which is related to video processing.
The first one is simply to invert an image. That is, a black pixel in the input
becomes a white pixel in the output etc. The equation for image inversion is defined
in Eq.
4.17
and an example is illustrated in Fig.
4.26
.
g(x,y)
=
255
−
f(x,y)
(4.17)
Another use of image arithmetic is
alpha blending
. Alpha blending is used when
mixing two images, for example gradually changing from one image to another
image. The idea is to extend Eq.
4.16
so that the two images have different impor-
tance. For example 20% of
f
1
(x, y)
and 80% of
f
2
(x, y)
. Note that the sum of the
two percentages should be 100%. Concretely, the equation is rewritten as
g(x,y)
=
α
·
f
1
(x, y)
+
(
1
−
α)
·
f
2
(x, y)
(4.18)
