non-linear brightness reduction?

[FredThompson]

I'm looking for a way to reduce the brightness of RGB pixels above a user-specified level. Essentially, those RGB pixels with a brightness which exceeds the trigger value should have their brightness reduced by reducing the brightness range.

To illustrate on a 100-point scale:

Suppose the trigger value is 80 and the maximum value is 90. This changes the brightness range for those pixels above 80 to a 10-point spread instead of the 20 starting points.

That's a very clean example and doesn't match actual video values but does illustrate the idea.

How can this be done with VirtualDub?

Asciiwhale's Parser (http://askywhale.free.fr/avi2ascii/parser.html) might be usable but I still can't figure the thing out.

Alexander Nagiller's gradation curve filter (http://members.chello.at/nagiller/VDub/) looks like it might do this type of thing but I'm each value has to be manually remapped. I'm really hoping for something with auto-ranging.

[rfmmars]

You might want to look at the "Autolevels plugin", it can be downloaded from Donold Graft's site or I can email it to you.

Anything that automatic scares hell out of me, but this is different. My business is telecine of old 8mm super 8mm, 16mm film to DVD.

You have many settings....white & black input levels, white and black strecth points, and rgb levels. This is a rewrite of the ACD-see plugin which had no adjustments.

I had a chance to redo a conversion that the client had done about 15 years ago. When he saw the proofing clip on one monitor and his old conversion on the other, he couldn't believe it, all the color were back.

Give it a try.

richard
photorecall.net

[FredThompson]

Which filter, specifically, are you talking about?

I'll take a look but that doesn't seem like what I'm looking for. Only those pixels over the trigger brightness level should be modified.

[rfmmars]

The filter is called "autolevels" it was first called ACD-SEE EOD. The one you want is the revised one. It's on Donald Graft's site with source.

Right now I have two workstations prossesing 2000 35mm slides for basicly what you are asking for. You can sit back with the two windows side by side, and when the video is good, you see no difference, but when there is a problem side, it is amazing.

It cost nothing to try it out and maybe you can customize the code.

richard
photorecall.net

[FredThompson]

I've looked through my stuff and found the filter you mentioned. EOD's filter is an attempt to lighten overly dark images. That's not what I'm looking for. I need to darken pixels which are over a specified brightness.