1. // Adrian Cruceru
    2. // Redshift Rendering Technologies 2020
    3. // This file is licensed under Apache 2.0 license
    4. // luma
    6. shader Luma
    7. [[  string help = "computes the relative luminance = luma of an input in various formats",
    8.     string label = "Luma/Relative Luminance" ]]
    9. (
    10.     // inputs
    11.     color inColor = 0
    12.     [[string label = "In Color"]],
    13.     // various modes to compute the relative Luminance
    14.     int mode = 0
    15.     [[  string label = "Mode",
    16.         string widget = "mapper",
    17.         string options = "Rec. 709 (HD):0|Rec. 2020 (4k):1|Ccir 601 (SD):2|Average:3|Red:4|Green:5|Blue:6"]],
    18.     float gamma = 2.2
    19.     [[  string label = "Gamma",
    20.         float min = 0, float max = 3 ]],
    21.     int preGamma = 1
    22.     [[  string widget = "checkBox",
    23.         string label = "Pre Gamma" ]],
    24.     int postGamma = 1
    25.     [[  string widget = "checkBox" ,
    26.         string label = "Post Gamma" ]],
    27.     // outputs
    28.     output color outColor = 1
    29.     [[  string label = "Out Color" ]]
    30. )
    31. {
    32.     // define various luma standards
    33.     vector rec709   = {0.2126,  0.7152, 0.0722};
    34.     vector rec2020  = {0.2627,  0.678,  0.0593};
    35.     vector ccir601  = {0.299,   0.587,  0.114};
    36.     float R = preGamma*pow(inColor[0],1/gamma)+(1-preGamma)*inColor[0];
    37.     float G = preGamma*pow(inColor[1],1/gamma)+(1-preGamma)*inColor[1];
    38.     float B = preGamma*pow(inColor[2],1/gamma)+(1-preGamma)*inColor[2];
    40.     if (mode == 0)
    41.     {
    42.         // internally the luminance function is using REC709
    43.         // outColor = luminance(inColor);
    44.         color C = rec709[0]*R +rec709[1]*G+rec709[2]*B;
    45.         color powC = pow(C,gamma);
    46.         outColor = postGamma*powC+(1-postGamma)*C;
    47.     }
    48.     else if (mode == 1)
    49.     {
    50.         color C = rec2020[0]*R+rec2020[1]*G+rec2020[2]*B;
    51.         color powC = pow(C,gamma);
    52.         outColor = postGamma*powC+(1-postGamma)*C;
    53.     }
    54.     else if (mode == 2)
    55.     {
    56.         color C = ccir601[0]*R+ccir601[1]*G+ccir601[2]*B;
    57.         color powC = pow(C,gamma);
    58.         outColor = postGamma*powC+(1-postGamma)*C;
    59.     }
    60.     else if (mode == 3)
    61.     {
    62.         color C = (R+G+B)/3;
    63.         color powC = pow(C,gamma);
    64.         outColor = postGamma*powC+(1-postGamma)*C;
    65.     }
    66.     else if (mode == 4)
    67.     {
    68.         outColor = postGamma*pow(R,gamma)+(1-postGamma)*R;
    69.     }
    70.     else if (mode == 5)
    71.     {
    72.         outColor = postGamma*pow(G,gamma)+(1-postGamma)*G;
    73.     }
    74.     else if (mode == 6)
    75.     {
    76.         outColor = postGamma*pow(B,gamma)+(1-postGamma)*B;
    77.     }
    78. }