[EXPERT TIPS][GUY
KUO][AVIA]
Detecting SVM presence vs. Sharpening
<< Back to Avia page
Scan Velocity Modulation (SVM) and edge
enhancement due to oversharpening are often both present in a display. While these
"enhancments" are desired by less critical viewers, their presence produces
geometric and object edge artifcacts which are anathema to realistic depiction of images.
The traditional method to look for SVM is comparison of the black and white portions of
the lines in a Needle Pulse pattern. AVIA adds a right hand side needle pulse to help
detect geometry distortions which would otherwise be missed using a traditional single
pulse pattern as in VE. There is another, simpler way to tell if SVM is present.
When SVM is active, the horizontal movement of the electron beam is slowed during
bright portions of the image. This slowing horizontally shrinks bright objects. Edge
enhancement due to over-sharpening does not geometrically distort objects in this manner.
We take advantage of this when comparing the line thickness in AVIA's Needle Pulses
pattern, but some people seem to have difficulty with that method.
Display the AVIA Checkerboard 100 IRE pattern (Title 2 Chapter 25) and you will see a
checkerboard of black and white. The corners of the pattern actually just touch each
exactly as in a real checkerboard, but if SVM is present this does not happen. You will
notice that the white tiles don't touch the corners of each other if SVM is active. That's
because SVM activity horizontally shrinks the white tiles (and hence stretches the black
tiles) making the WHITE tiles fail to touch each other's corners.
This makes for a quick and easy way to determine if SVM has actually been turned off
should there be confusion over whether or not a poorly labeled service control changes
sharpness vs SVM.
If the white tile corners touch each other, SVM is off. If the white tile corners fall
short of each other horizontally, SVM is on.
|
