Phytec eGrabber-4plus, Руководство по оборудованию

Страница: 132 / 206

eGrabber-4plus
122 
PHYTEC Meßtechnik GmbH 2004 L-608e_4
Examples:
l
field-based digitizing
A quadratic image of the size 256 x 256 pixels should be digitized
with a resolution and proportion corresponding to the TV picture.
(a) Resolution and Scaling
For digitization a field (288 lines) is sufficient. In order to obtain a
correct width/height ratio, the resolution in X-direction has to be
reduced to the half (since field = half height).
Therefor 720:2 = 360.
The result is : ppl=360, lines=288
(b) Size of the section
The image should have a quadratic size of 256 x 256 pixels.
The result is : hsize=256, vsize=256
(c) Positioning
It is advisable to center the section of the image.
In x-direction only 256 pixels of 360 pixels are displayed in the
window. At the edge 360 – 256 = 104 pixels remain, which are
divided in equal parts to both sides, which result in 52 pixels on
both sides. hpos is the size of the left edge, so hpos=52.
Correspondingly in Y-direction: (288-256):2=16; vpos=16.
Note:
It would be wrong to set ppl=256 and lines = 256. In this case the
width/height ratio (TV-Norm 4:3) would be changed to 1: 1 and
the image would be distorted. It would be possible to set
lines = 256 and to compute ppl by the width/height ratio. In this
case we would gain the optimal height of the image.