Adjusting Lightness using ColorMatrix

Question

I'm trying to adjust the lightness of an image (You can see this option in Photoshop when trying to adjust the Hue, also lightness and brightness are two different features) using ColorMatrix but am lost on which values to change to achive this.

Currently I'm able to change the Hue using this code

public static void adjustHue(ColorMatrix cm, float value)
    {
        value = cleanValue(value, 180f) / 180f * (float) Math.PI;
        if (value == 0)
        {
            return;
        }
        float cosVal = (float) Math.cos(value);
        float sinVal = (float) Math.sin(value);
        float lumR = 0.213f;
        float lumG = 0.715f;
        float lumB = 0.072f;
        float[] mat = new float[]
        { 
                lumR + cosVal * (1 - lumR) + sinVal * (-lumR), lumG + cosVal * (-lumG) + sinVal * (-lumG), lumB + cosVal * (-lumB) + sinVal * (1 - lumB), 0, 0, 
                lumR + cosVal * (-lumR) + sinVal * (0.143f), lumG + cosVal * (1 - lumG) + sinVal * (0.140f), lumB + cosVal * (-lumB) + sinVal * (-0.283f), 0, 0,
                lumR + cosVal * (-lumR) + sinVal * (-(1 - lumR)), lumG + cosVal * (-lumG) + sinVal * (lumG), lumB + cosVal * (1 - lumB) + sinVal * (lumB), 0, 0, 
                0f, 0f, 0f, 1f, 0f, 
                0f, 0f, 0f, 0f, 1f };
        cm.postConcat(new ColorMatrix(mat));
    }

I want to understand on how to use the colormatrix to change the lightness in the same way. If there is any other way of achieving this, I'm open for solutions :)

Answer 1

Ok..So I finally figured this out.

Lightness can be adjusted using the PorterDuffColorFilter Class

Here's the method that I'm using

public static PorterDuffColorFilter applyLightness(int progress) {

    if(progress>0)
    {
        int value = (int) progress*255/100;
        return new PorterDuffColorFilter(Color.argb(value, 255, 255, 255), Mode.SRC_OVER);
    } else {
        int value = (int) (progress*-1)*255/100;
        return new PorterDuffColorFilter(Color.argb(value, 0, 0, 0), Mode.SRC_ATOP);
    }

}

The value of progress is from -100 (dark) to 100(bright)

Just pass the values as in photoshop to this method. The filter that you get can be used with paint and canvas.

Hope this helps someone.

Answer 2

You can use this to change lightness

public static void adjustLightness(ColorMatrix cm, float value)
{
    value = cleanValue(value, 100);
    if (value == 0)
    {
        return;
    }

    float[] mat = new float[]
            {
                    1,0,0,0,value,
                    0,1,0,0,value,
                    0,0,1,0,value,
                    0,0,0,1,0,
                    0,0,0,0,1
            };
    cm.postConcat(new ColorMatrix(mat));
}

//Helper method
protected static float cleanValue(float p_val, float p_limit)
{
    return Math.min(p_limit, Math.max(-p_limit, p_val));
}

You can read more here, but I'd recommend you to use RenderScript because of it's speed.