Decomb vthresh Clarification
Posted: Sat Jun 01, 2013 6:52 pm
I'm trying to IVTC DVD content, but I'm having trouble understanding the best way to set the vthresh value. From what I can tell by taking screenshot comparisons and using post=3 and show=true, it's necessary to select a high enough vthresh value to detect all combed frames, as a value that's too low will allow some combed frames to slip through into the output file. Most of the time, it's sufficient to use vthresh values in the 30-60 range (which is near the default setting of 50), but I've seen some frames with a "chosen" vmetric > 180 at times, which would require using a pretty high vthresh value.
If the vmetric can vary so widely, and as the manual says, "It's better to catch some progressive frames than to miss some combed ones," my question is: why isn't the vthresh value just set at the maximum of 255 all the time, rather than defined as a user-controlled parameter? Is it just because setting a high vthresh value results in slower processing, or is there some sort of quality degradation that occurs from catching all of the progressive frames by using a high vthresh to ensure that no combed frames remain in the output?
The manual also says that you can define "zones" where vthresh values can differ between different points in the same clip, so I assume that feature exists because there is some drawback to using a high vthresh value for the entire clip "just to be sure", so to speak. Is it possible to reduce the range of possible vmetric values by tweaking another parameter, or would that yield essentially the same result as using a high vthresh?
Note: I'm working with anime content, if that is important. The Doom9 IVTC guide says it is one of the most difficult things to process, which I suppose means I've chosen an arduous task. Thanks for any advice you might be able to provide.
If the vmetric can vary so widely, and as the manual says, "It's better to catch some progressive frames than to miss some combed ones," my question is: why isn't the vthresh value just set at the maximum of 255 all the time, rather than defined as a user-controlled parameter? Is it just because setting a high vthresh value results in slower processing, or is there some sort of quality degradation that occurs from catching all of the progressive frames by using a high vthresh to ensure that no combed frames remain in the output?
The manual also says that you can define "zones" where vthresh values can differ between different points in the same clip, so I assume that feature exists because there is some drawback to using a high vthresh value for the entire clip "just to be sure", so to speak. Is it possible to reduce the range of possible vmetric values by tweaking another parameter, or would that yield essentially the same result as using a high vthresh?
Note: I'm working with anime content, if that is important. The Doom9 IVTC guide says it is one of the most difficult things to process, which I suppose means I've chosen an arduous task. Thanks for any advice you might be able to provide.