![background image](http://html1.mh-extra.com/html/snell-and-wilcox/arc130s/arc130s_operators-manual_1309051053.webp)
ARC130S SECTION
5
System Overview
ARC130S 060801 Version 1 Issue 1
5.1
The ARC130S is a digital-in digital-out Aspect ratio
Converter.
To change the aspect ratio, the picture has to be
stretched or compressed in either or both the
horizontal and vertical plane. To stretch or
compress the picture, data has to be interpolated
from adjacent pixels.
The ARC130S vertical temporal interpolation
operates on four fields and six lines of the
incoming video and is effectively a 24-point filter
(optimised individually for every pixel point of the
picture). Filtering is carried out separately for
luminance and chrominance. A large horizontal
filter is applied after the vertical filter.
There are two factors influencing the performance
of the interpolation, one is the number of points
being used in the filter, and the other is the need to
carry out vertical-temporal interpolation. To explain
the latter factor, six lines on one field would only
access half the information in the interlace system
but when we use 12 lines from a full frame, the
information in the second field is displaced in time
from the first field; this must be taken into account
when interpolating.
In the diagram you are looking at the lines of the
video structure end-on as if you are looking into the
side of the CRT face while the pixels of four fields
are displayed. The field offset of the required pixel
from field 2 is the temporal offset and the line
offset from the nearest line in field 2 is the vertical
offset. The area shaded is the aperture which is
centred on the required pixel position. A proportion
of every pixel in the aperture is used in creating the
new pixel; the proportions diminish as the distance
from the required pixel increases.
In addition to changing the picture aspect ratio, the
unit can read and act on line 23 signalling on the
input signal and can insert line 23 signalling on the
output.