Limiter - does it work correctly?

[Si]

There's a discussion going on in usage (http://forum.doom9.org/showthread.php?s=&threadid=57778&perpage=20&pagenumber=1) about Limiter.

It prompted me to start writing a plugin to try and check the Y,U and V levels in YUY2 colourspace (ShowLevels)

I started to get unexpected results - e.g. my main TNG Huffyuv test capture clip seemed to have Y levels above 235 :( :o

So I put Limiter() in my script to see if was a problem with my filter or "real" and I found Limiter didn't make any difference. :confused:

So I went lookin on Avisynth.org to see if it needed parameters and found the documentation says it defaults to limiting Y levels to 236 :confused: :confused:

So my questions to the experts at this point are
1. Should it not be 235?
2. Is it the documentation thats wrong and/or the filter?
3. Or is it me :o

My experimental ShowLevels is available here (Version 0 in debug mode!) (http://geocities.com/siwalters_uk/showlevelsdbg.zip) (Need to right-click and use Save As)

It should just show Y levels above 235 as white pixels but I wouldn't fully trust it yet :o

regards
Simon

[sh0dan]

I made it default 236 for some strange reason - think it had something to do with histogram.

[Si]

Could/would you change it to 235 please :)
regards
Simon

[sh0dan]

Sure - for now you can just use limiter(16,235)

[mikeson]

I'm a little bit confused now... :)

What is right use of limiter? limiter() or should we use limiter(16,235)?

[Si]

IMO Limiter(16,235)

Simon

[Sigmatador]

Am i wrong if i think that, even if i put a limiter(16,235) at the end of my script, my xvid encode will not respect this limited value because of the compression ?

[Si]

Try it :)

Put ColourYUV(analyse=true) at the end of your script and see if it needs Limiter at all.


Encode the script (with Limiter in it) using XVid to a test file

Then use this script

Avisource("XVidTest.avi")
ColorYUV(analyze=true)

and feed it into VirtualDub(Mod) to see if it has had any effect.

regards

Simon

[sh0dan]

Quantizer rounding may produce values outside the CCIR range, but it will not really matter, as it will display as the original data.

BTW: If you use limiter() or the suggested setting above will not have any significant impact on your result (if any at all). There are a thousand things more important than that.