Another Avia Question - Sharpness Level

Discussion in 'Archived Threads 2001-2004' started by Dave H, Dec 21, 2001.

  1. Dave H

    Dave H Producer

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    Since disabling SVM, my pictures looks SO much better. Gone is the ringing and bad edge enhancement. DVDs look so much more filmlike. However, the picture is a bit softer looking.

    Prior to disabling SVM, I had my sharpness at zero. While the sharpness pattern hasn't changed since getting rid of SVM, I tried increasing the sharpness just a little bit and I automatically noticed the "white outline" or noise being added to a black thin line in the center of the pattern. Now, despite the added white noise on the pattern, the black lines do get sharper.

    So, what I'm asking is whether having a little white noise is ok if it sharpens the black lines, or whether ANY increase in sharpness should be halted once the white noise is evident? Is any white tolerable? Or, is about compromise (similar to black vs. shadows while adjusting black level)?
     
  2. Guy Kuo

    Guy Kuo Supporting Actor

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    A little bit of white outlining in those lines is acceptable. The better measure to look at on the pattern is the evenness of the frequency sweep at the top of the pattern. Adjust sharpness to make that even in brightness but without overenhancing any frequencies. The black lines in the center of the pattern are very severe tests which practically no DVD playback device except a home theater PC can reconstruct at full bandwidth. On consumer players, a little bit of outlining is normal.

    Because of this restriction in consumer DVD players, the new sharpness pattern in Home Theater Tune-up has intentionally limited bandwidth in its lines to avoid the appearance of any white outlining.
     
  3. Joe Ferrari

    Joe Ferrari Agent

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    Should I turn my scan velocity modulation down to zero on my RPTV? I know the service code to do it I was just wondering why. I don't really know what it is or does.

    Thanks,

    Joe
     
  4. Guy Kuo

    Guy Kuo Supporting Actor

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    Scan velocity modulation is a strategy which is used to increase peak contrast and reduce the blurring of the electron beam during momentary high beam energies. SVM works by retarding the normally constant rate at which the electron beam is painted across the screen during bright portions of the picture. If done well, it can make small, bright image details smaller and brighter than normally possible.

    Unfortunately, SVM also creates geometry distortions and falsely enhanced edge transitions. You can see the geometry distortions created by SVM activity by viewing the checkerboard pattern in AVIA. The black and white square's corners actually meet each other just like a checkerboard. If SVM is active, the beam is slowed during the white squares so the white squares end up horizontally shorter than the black squares. The corners no longer touch each other as normal.

    Since, home theater contrast level settings are lower than torch mode, the increased peak level and sharpening done by SVM isn't beneficial. One gets the disadvantage of SVM but not the advantages when contrast level is set low. For home theater viewing SVM is therefore not a feature but something which distorts the image more than it helps the image. Turning it off removes one source of image distortion which can be avoided.
     

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