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.