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Interpolating between two HSL Values


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I am attempting to interpolate between two different HSL value, but I can't seem to figure out why this does not work:

double lerp(double a, double b, double t){
    return a * (1 - t) + b * t ;
}

ColorBgra out_hsl(double hue_a,double hue_b,double sat_a,double sat_b,double intensity_a,double intensity_b,double pos){
    //new_pos is always in range [0,1).
    double new_pos = pos - Math.Floor(pos);
    double H = lerp(hue_a,hue_b,new_pos);
    double S = lerp(sat_a,sat_b,new_pos);
    double L = lerp(intensity_a,intensity_b,new_pos);
    int section = (int)(H/60);

    double C=(1 - Math.Abs(2*L-1))*S;
    double X=C*(1-Math.Abs((double)(section%2-1)));
    double m = L - C/2;
    double red,green,blue;
    switch(section){
        case 0:
        red = C; green = X; blue = 0;
        break;
        case 1:
        red = X; green = C; blue = 0;
        break;
        case 2:
        red = 0; green = C; blue = X;
        break;
        case 3:
        red = 0; green = X; blue = C;
        break;
        case 4:
        red = X; green = 0; blue = C;
        break;
        default:
        red = C; green = 0; blue = X;
        break;
    }
    red=(red+m)*255;
    green=(green+m)*255;
    blue=(blue+m)*255;
    return ColorBgra.FromBgraClamped((int)(blue),(int)(green),(int)(red),255);
}

 

I have used this source : https://www.rapidtables.com/convert/color/hsl-to-rgb.html

 

It should work because the formula used here are the same.

Edited by Reptillian

G'MIC Filter Developer

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Well, I already solved it.  I solved it by isolating the HSL2RGB function into a test code, and figured what's wrong. For anyone stumbling upon this problem:

 

ColorBgra hsl2rgb(double H,double S,double L){
    int iH = (int)(H)/60;
    double C = (1-Math.Abs(2*L-1))*S;
    double X = C * (1 - Math.Abs((H/60)%2-1));
    double m = L - C/2;
    double tr,tg,tb;
    switch(iH){
        case 0:
            tr=C;
            tg=X;
            tb=0;
            break;
        case 1:
            tr=X;
            tg=C;
            tb=0;
            break;
        case 2:
            tr=0;
            tg=C;
            tb=X;
            break;
        case 3:
            tr=0;
            tg=X;
            tb=C;
            break;
        case 4:
            tr=X;
            tg=0;
            tb=C;
            break;
        default:
            tr=C;
            tg=0;
            tb=X;
            break;
    }
    tr+=m;
    tg+=m;
    tb+=m;
    tr*=255;
    tg*=255;
    tb*=255;
    tr=Math.Round(tr);
    tg=Math.Round(tg);
    tb=Math.Round(tb);
    return ColorBgra.FromBgraClamped((int)(tb),(int)(tg),(int)(tr),255);
}

 

Edited by Reptillian

G'MIC Filter Developer

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