Autogain Issue in AVISynth and VirtualDub

[Gramps]

Hi,

I have been working on cleaning up some old music videos that I have. As part of that exercise, I've been attempting to use the AVISynth ColorYUV(autogain=true) filter to improve the brightness/contrast/gamma/color. I am using VirtualDubMod to open and tweak the AVS files. Anyway, the output video looks beautiful as a result, except for one problem.

In the videos, anytime there is a scene transition that uses a fade to totally black, the Autogain seems to freak out and displays the black frame as very severe white blocks. As soon as the next scene starts, Autogain goes back to working correctly.

As an experiment, I've also tried the AutoLevels 0.3 AVISynth filter. Again, beautiful output except for the severe white blocks that appear on black frames. HDRAGC doesn't exhibit the behavior, but it doesn't give nearly as nice output. In VirtualDubMod, I see the same effect if I try the MSU ColorEnhancement filter or the latest version of the VirtualDub AutoLevels filter as well. Interestingly enough, the older versions of the AutoLevels filter don't exhibit the behavior. I also have tried the videos in the latest version of VirtualDub. Same issue.

I've tried converting the videos to different colorspaces and tried setting the levels to "blacken" the black frames with the hope that the filters would see them as black and leave them alone. I've also tried moving the ColorYUV and AutoLevels to different points in the AVS script filter chain to see if that fixed it. Same behavior.

Has anyone seen this before and know of a solution?

Thanks!

[poisondeathray]

I'm fairly new to avisynth and still learning, but one possible way is to apply filter to segments e.g. 1000 frame video

a=avisource().trim(0,100).coloryuv()
b=avisource().trim(101,500)
c=avisource().trim(501,1000).coloryuv()

a+b+c

Something like that; in this example frames 101 to 500 are unfiltered. Of course you have to fill your arguments for coloryuv, and use proper paths/names. You could also use DirectShowSource(), or FFMpegSource(), etc...

I've also learned that how you view the video makes a big difference, e.g. if you are using VRM9 to render, colors are usually washed out, blacks are faded etc.., compared to video overlay. You can get around these problems by forcing RGB in ffdshow (if you use a directshow player like MPC), or just using differnt renders/overlays - but the underlying video may be perfectly normal

I've also learned to keep the filter chain (thru graphedit and the external filters in mpc) as clean as possible, or there are unexpected compounding effects (like color conversions).

I think Vdub automatically converts to RGB (at least in the preview window, and also internally if you use "full processing" as opposed to "fast recompress" while encoding), so the colors in the preview should look "normal"

Finally different video drivers and display settings might not be calibrated to full PC range or TV range RGB...This may have an effect on viewing

[manono]

HDRAGC doesn't exhibit the behavior, but it doesn't give nearly as nice output.

I was going to suggest HDRAGC until I saw that. Have you read the doc thoroughly and tried using some of the settings to achieve what you want? I find it does a great job with some tweaking, but you weren't very specific about what you didn't like about it.

I find the Autogain to be really horrible, partly for the reason you mentioned. The AutoLevels filter is just as bad. I wish the guy would get that one fixed, because otherwise it's pretty good.

By the way, before applying HDRAGC I tweak the Brightness and Contrast if they need it, using the Tweak Filter. To test I stick this at or near the bottom of the script:

ColorYUV(Analyze=True)
Limiter(Show="Luma")

You can learn a lot about what needs to be done by having a look after applying those 2.

[Gramps]

HDRAGC doesn't exhibit the behavior, but it doesn't give nearly as nice output.

I was going to suggest HDRAGC until I saw that. Have you read the doc thoroughly and tried using some of the settings to achieve what you want? I find it does a great job with some tweaking, but you weren't very specific about what you didn't like about it.

I find the Autogain to be really horrible, partly for the reason you mentioned. The AutoLevels filter is just as bad. I wish the guy would get that one fixed, because otherwise it's pretty good.

By the way, before applying HDRAGC I tweak the Brightness and Contrast if they need it, using the Tweak Filter. To test I stick this at or near the bottom of the script:

ColorYUV(Analyze=True)
Limiter(Show="Luma")

You can learn a lot about what needs to be done by having a look after applying those 2.

Thanks manono! I'll take a look at those filters. What I don't like about HDRAGC is that, while it brightens the video, it doesn't seem to deal with chroma corrections and saturation levels very well, especially if they change throughout the clip. Also, as it brightens a frame, the black areas also get brightened and washed out. Maybe it is time to re-read the instructions.

[manono]

Yeah, the problems you mentioned can happen if using the default settings. Doing something like this might help a bit:

HDRAGC(Corrector=0.8,Reducer=1.5)

The Reducer setting helps control the noise in dark and black areas, something that absolutely ruins ColorYUV(Autogain=True) and the AutoLevels filter. The Corrector setting keeps it from being brightened too much. He has a setting that boosts saturation, but I usually use Tweak for that. There are a couple of settings that can help with the washed out black levels. Reading the original Doom9 thread might prove useful, if you haven't seen it already:

http://forum.doom9.org/showthread.php?t=93571