The gamma level formula goes wrong?

Hello

I am teaching how to build a Pixel Bender (2.5) plug-ins for AE CS5 by porting a FCP FXScript I wrote recently.

I do some [other stuff] to the image and it works fine, but after other functions, I want to allow the adjustment of the red channel of the image gamma correction, and so I have a parameter:

parameter float redGamma

<

minValue: 0.01;

maxValue: 5.0;

defaultValue: 1,0;

stepInterval: 0.01;

displayName: "Red channel Gamma."

>;

.. .and then I apply the change gamma later in the script, with what I understand, this is the formula of standard gamma correction:

SRC.r = pow ((src.r / 255.0), redGamma/1.0) * 255.0;

However, the range is not in the same way to the effect of AE normal levels, where it crashed into the black around gamma 0,0 and died in the red suit at about 5.0. In the formula I put in place, levels crash to around 0.5 gamma black and Red full to about 1.66.

Is there a scale factor or another Exhibitor the levels effect incorporated EI use that I am missing, or something else that I'm not wrong?

Thank you!

MB

I'm not an expert on gamma, or AE applied on the way, but I'm suspicious about your use of the constant 255.0. Once you run in a PB filter color values are floats in the range 0.0-1.0. The formula that you quoted seems to be asuming that color values 0-255 and it's a necessary step, and I suspect incorrect conversion.

If you leave the / 255.0 and the * 255.0 do the results match what you expect?

Tags: Pixel Bender

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