Quantcast Need to brighten the dark video with AVISynth - digitalFAQ Forum
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02-20-2014, 03:38 PM
metaleonid metaleonid is offline
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Hello,

Preface.

I digitized the video from Hi8. Some parts of video were shot during day time while other parts were shot at night. When I digitized it, I decided used my Philips SAA7134 chip based capture card with manual gain level set to 37 out of 100. When I initially set gain level to 50 (default), the brighter parts were a bit of blown up and had no details. Setting gain to 37 gave perfect details on white parts. However, the black level was kind of blown up. But the thing is that while I can't seem to be able to fix white level as post processing, the black level seems to be fixable.

I loaded the footage with gain 50 in VirtualDub and reduced brightness. I couldn't get back the details that were missing. But when I loaded the footage with gain 37 and increased brightness, I was able to get all the dark details that seemed to be invisible if no brightness applied.

So the question is...

Can someone recommend me AVISynth settings such that I can bright up dark parts to restore details while leave bright parts almost unchanged or brighten them without losing details. Thanks.

--Leonid

PS. The video was initially digitized by my friend who plugged his Hi8 camera into his DV camera and then ran FireWire output of the latter to his desktop computer. His footage is good as far as DV goes. But the white level is blown up a bit while the black level seems to be perfectly fine. I told him that DV is not as good as Huffyuv and asked him to give the Hi8 tape and his camcorder to me to redo it in Huffyuv. So I really don't want to be in the situation that the video that I made in Huffyuv looks worse than his DV version.
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  #2  
02-21-2014, 06:10 AM
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lordsmurf lordsmurf is offline
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Trying to perfect color correction with a scripted video tool is almost impossible. I use Adobe Premiere, VirtualDub and sometimes TMPGEnc Plus for correcting color.

I can do it, but never do. The settings are too rough, and not as nuanced as GUI editor.

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02-21-2014, 07:57 AM
metaleonid metaleonid is offline
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What's GUI editor?
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02-24-2014, 10:58 PM
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lordsmurf lordsmurf is offline
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GUI = graphical user interface. You click stuff. You don't type up scripts, or use a command line (DOS, Linux SSH, etc).
- Adobe Premiere is a GUI
- Avisynth is not.

There's an auto white balance filter for Avisynth. Have you tried that?

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02-25-2014, 06:58 AM
metaleonid metaleonid is offline
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Oh, I know what GUI is. i thought you had a specific GUI editor in mind that I could download and try. Thanks.
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07-23-2014, 07:11 AM
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lordsmurf lordsmurf is offline
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Just to add, AvsPmod (Avisynth GUI) has sliders for some filters. However, I never use it -- nor color grading in Avisynth -- so you'd just need to load it and see.

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07-23-2014, 07:57 AM
sanlyn sanlyn is offline
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This thread is a couple of months old, but.....

The original question for recommended Avisynth settings is impossible to answer in detail. With every source, especially analog home-made source, you'll encounter anything and everything. The chaotic changes are like a Marx Brothers movie. Levels and color balance change minute by minute, and even during scenes. The only hard and fast rules are those that you can deduce from looking over Avisynth's descriptions for ColorYUV, Tweak, and Levels parameters. The same linked articles are in the documentation installed with Avisynth, which you've probably seen by now.

Your description of the way you fixed the levels problem is a typical way of doing it. You've also seen how different values affect different parts of the image. Almost everything you do with this type of correction will vary with the source, which means that settings will have to suit the source. The best way to figure out what all those different settings do? Using them and observing what happens is probably the best way. It also helps to use a histogram or other graphic display to help you understand what's happening in detail. Here is a link to a still photo tutorial on how to read one type of histogram. It's a photo site, but the principles for all graphics are pretty much the same: http://www.cambridgeincolour.com/tut...istograms1.htm .

Usually (I repeat, usually) I first make basic levels and color corrections in YUV with Avisynth. Often those corrections will be good enough. The idea is to rescue bad darks and brights before conversion to colorspaces such as RGB, if RGB is required. Avisynth's SmoothAdjust plugin is another useful YUV tool (works in YV12 only). You can do only so much in YUV. For really serious tweaking and color grading you're likely to have to use RGB controls such as VirtualDub's ColorMill or gradation curves.

Lordsmurf mentioned the image controls in TMPGEnc Plus 2.5, which are quite clever and can fix a lot of problems. TMPGEnc Video Mastering Works has simialar controls. Note that those filters work in both YUV and RGB. Make YUV corrections first, then chain RGB-only filters as needed. The color controls in budget NLE's like Premiere Elements are rather basic and not really suited for cranky color problems. Higher-end apps like Premiere Pro, AfterEffects, Vegas Pro, etc., are far more sophisticated and precise. Several VirtualDub filters are similar to the high-end guys, but not as fancy.

There are hundreds of free internet tutorials on this subject that are very instructive. Almost all of them are associated with high-end apps or still cameras, but as I say the principles are the same. Why video sites spend more time on noise reduction (which is important, of course) but so little time on using similar Avisynth and VirtualDub filters in detail is a mystery to me. Many noise problems are impossible to fix completely, but decent levels and color can often mask those problems and make them seem less obvious.
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