ADS Technologies USBAV-708 INSTANT VIDEOMPX, User Manual

Page: 69 / 116

The
Guide
69
Cro
p
a
nd
Re
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Re
size
Resizing scales the video dimensions on one or both axis.
You can select the type of sampling that is performed in
the source image to calculate the color of each pixel in the
resized image. Different sampling options create slightly different
effects in the resized image.
Bilinear sampling is best used when reducing an
image. The color of each pixel in the resized image
depends on where the pixel would fall in the source
image.
The color is interpolated from the four surrounding
pixels based upon the theoretical position of the
new pixel.
Because bilinear sampling considers only 2x2 pixels
in the source and interpolates linearly it produces a
softened image on resizing and can cause pixelation
in enlarged images.
Bicubic sampling is more complex than bilinear
sampling, calculating the color of each pixel in the
resized image from 4x4 pixels in the source
Instead of simply interpolating linearly between
pixels bicubic sampling weights the contribution of
each pixel in the source using a spline function
based upon the offset of each pixel from the pixel
being calculated.
Changing the spline parameters allows the
sharpness of the resized image to be controlled.
Three presets -
soft , normal and sharp —are
available to choose from.
Bicubic sampling produces better quality over
bilinear sampling when enlarging an image but
because more samples are taken and calculations
are more complex for the bicubic method it also takes longer to compute.
QUICK GUIDE
Resize
35% 65%
30%
70
%
New color =
70%( 65% + 35% ) +
30%( 65% + 35% )
Linear
Offset
Co
ntr
ib
uti
on
Bicubic (soft)
Offset
Co
ntr
ib
uti
on
Bicubic (normal)
Offset
Co
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ib
uti
on
Bicubic (sharp)
Offset
Co
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ib
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on
0 2 1 0 1
0 2 1 0 2 1
Source Bilinear resample Bicubic resample