[opendtv] Re: Precision
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Thu, 31 May 2007 09:34:09 -0400
At 8:16 PM -0400 5/28/07, Allen Le Roy Limberg wrote:
The discussion seems to dwell on the type of resolution sometimes referred
to as "fine line" resolution -- i.e. how small a detail can be reproduced.
An important type of resolution in displays is "edge" resolution -- i.e. how
accurately a diagonal line can be positioned and how well well "jaggies" can
be suppressed. This doesn't involve extended frequency response, but rather
accurate phase response of the frequency components of the video image. Jim
Davis out at RCA avionics in Van Nuys, CA pointed this out in a patent I
filed for him 35 years ago or so, as I recall.
Fewer lines in the display hurts the angular resolution of an edge and
lowers the step frequency making jaggies more visible. The human visual
system is quite sensitive to jaggies. We easily espy low-spatial-frequency
parts of a display being out of correct spatial or temporal position, while
superposed random noise is largely disregarded.
Video compression may have fewer problems with accurately defining phase
response of the moving edge than with defining moving fine line detail.
Good points. As I just noted in a response to Tom, excessive
quantization can cause major problems in the areas of high frequency
edges. We can only provide accurate edges IF we do not quantize them
excessively. Unfortunately just the opposite is what is happening.
The edges are the first thing to fall apart when we compress too
much, whereas, in blocks with uniformly distributed fine details we
just replace those details with correlated noise.
Regards
Craig
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