i'm not sure it's what i need. It changes rgb gamma and i need change gamma for each channel (like in photoshop).

i posted screen shot what i looking for

thanks for your reply! so, if i wanna change gamma for each channel separately i have to change your code so:

dst.rgb = pow(dst.rgb, float3(red[1], green[1], blue[1])/gammaRGB)

where red[1], green[1], blue[1] are the parameters of gamma

i compared the result which i've got and it's different from photoshop's

so, now my code looks like this

{

    parameter float3 red

    <

        minValue: float3(0.0,0.0,1.0);

        maxValue: float3(1.0,1.0,1.0);

        defaultValue: float3(0.0,1.0,1.0);

    >;

 

 

    parameter float3 green

    <

        minValue: float3(0.0,0.0,0.0);

        maxValue: float3(1.0,1.0,1.0);

        defaultValue: float3(0.0,1.0,1.0);

    >;

 

 

    parameter float3 blue

    <

        minValue: float3(0.0,0.0,0.0);

        maxValue: float3(1.0,1.0,1.0);

        defaultValue: float3(0.0,1.0,1.0);

    >;

 

 

    parameter float3 RGB

    <

        minValue: float3(0.0,0.0,0.0);

        maxValue: float3(1.0,1.0,1.0);

        defaultValue: float3(0.0,1.0, 1.0);

    >;

 

    input image4 src;

    output pixel4 dst;

 

 

    void

    evaluatePixel()

    {

        pixel4 p = sampleNearest(src,outCoord());

 

        float rgbdiff = RGB[2] - RGB[0];

 

        p.r = ( (p.r - red[0])/(red[2] - red[0]) - RGB[0])/rgbdiff;

        p.g = ( (p.g - green[0])/(green[2] - green[0]) - RGB[0])/rgbdiff;

        p.b = ( (p.b - blue[0])/(blue[2] - blue[0]) - RGB[0])/rgbdiff;

 

        p.rgb = pow(p.rgb, float3(red[1], green[1], blue[1]) / RGB[1]);

        dst = p;

    }

}

upd: i tried to apply this filter again and it seems to me it works! Thank you very much for your correct answer. Maybe you know how to use photoshop's 'output panel', this parameter increases/decreases values of channel. Photoshop has this parameter in the bottom of level's panel.