Image Processing Reference

In-Depth Information

Fig. 4.26
Input image and

inverted image

Fig. 4.27
Examples of alpha blending, with different alpha values

where
α

∈[

0
,
1

]

and
α
is the Greek letter “alpha”, hence the name alpha blending.

If
α

0
.
5 then the two images are mixed equally and Eq.
4.18
has the same effect

as Eq.
4.16
.InFig.
4.27
, a mixing of two images is shown for different values of
α
.

In Eq.
4.18
,
α
is the same for every pixel, but it can actually be different from

pixel to pixel. This means that we have an entire image (with the same size as

f
1
(x, y), f
2
(x, y)
and
g(x,y)
) where we have
α
-values instead of pixels:
α(x,y)
.

Such an “
α
-image” is often referred to as an
alpha-channel
. This can for example

be used to define the transparency of an object.

=

4.7

Programming Point Processing Operations

When implementing one of the point processing operations in software the follow-

ing is done.