Digital Signal Processing Reference
In-Depth Information
Original pixels
2
1
4
New pixels
1
2
2
Co-eff: 1, 0
Co-eff: 0.75, 0.25
Co-eff: 0.25, 0.75
Co-eff: 0.5, 0.5
Figure 5.4.
The weighting coefficients for each pixel are given below.
New pixel 1 will just be a copy of the original pixel 1.
New pixel 2 will weigh 75% of original pixel 1 and 25% of
original pixel 2.
New pixel 3 will weigh 50% of original pixel 1 and 50% of
original pixel 2.
New pixel 4 will weigh 25% of original pixel 1 and 75% of
original pixel 2.
These are the simplest scaling algorithms and in many cases
these suffice for video scaling.
It's easy to see how this method of creating a pixel can be
increased in complexity by using more and more original pixels.
For example, you can choose to use nine original pixels each
multiplied by a different coefficient to calculate the value of your
new pixel.
Figure 5.5
shows an example of what is known as bicubic
scaling, or 4
4 matrix of image pixels is
downscaled by a factor of four in both the horizontal and the
vertical dimension
4 scaling. A sample 4
4 matrix of pixels is reduced to
a single pixel. The four pixels in the vertical dimension are scaled
first
so a 4
e
these four pixels belong to four different lines of video in
that frame.
By using any appropriate set of coefficients, the four pixel
values are converted into a single pixel value. This is then
repeated for the next four pixels, and so on. Finally we are left
with four pixels. These are further reduced to a single pixel by
e
