Impose limits to autogain

[filo74]

I wish to autolevel the B&W movie about Pitkin.
Usually I copy some representative frame from VirtualDub with Ctrl+1 to Photoshop. Then press Ctrl+L and watch for darker and lighter position of channels. I made very intuitive efforts to level each RGB channel individually using AdjustRGB and levels together in the past, but usually they can be adjusted alltogether. By the way I wonder why there is no script parameters support for Levels to work on each channel separately 8-(. And if the function exists why it is not called Levels?

The greyscale movie (about Pitkin) (when I copy some frames to Photoshop) shows that some scenes need like levels(28, 1, 233, 0, 255) but some need up to levels(60, 1, 218, 0, 255). If I use ColorYUV(autogain=true) it does all the work, but here comes another tradeoff - the dark frames between scenes become consisting of large squares of bright white and black :eek:. It happens because autogain adjusts the levels of those frames to something like levels(105, 1, 110, 0, 255).

I need a way to limit the autogain function to some... degree? - I am afraid to call it a maximum or minimum.

[hartford]

Well, to me, the solution seems obvious: do not use "autogain."

Cut the movie into seperate pieces and apply levels to each piece,
then join the processed pieces.

[foxyshadis]

http://forum.doom9.org/showthread.php?p=829019#post829019

Just discussed a solution there. Also, a white balance filter is around here somewhere that also does better than autogain. Autogain's implementation is basically exactly as you say, it fully relevels every frame individually, whereas hdr has a delay factor built-in.