Draw image on top of another image with blending mode color

Question

In Photoshop you can select \"Color\" (the second from the bottom) to set the blending mode to the next lower layer:

Answer 1

Here is my solution. I've used Rich Newman's HSLColor class to convert between RGB and HSL values.

using (Bitmap lower = new Bitmap("lower.png"))
using (Bitmap upper = new Bitmap("upper.png"))
using (Bitmap output = new Bitmap(lower.Width, lower.Height))
{
    int width = lower.Width;
    int height = lower.Height;
    var rect = new Rectangle(0, 0, width, height);

    BitmapData lowerData = lower.LockBits(rect, ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
    BitmapData upperData = upper.LockBits(rect, ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
    BitmapData outputData = output.LockBits(rect, ImageLockMode.WriteOnly, PixelFormat.Format24bppRgb);

    unsafe
    {
        byte* lowerPointer = (byte*) lowerData.Scan0;
        byte* upperPointer = (byte*) upperData.Scan0;
        byte* outputPointer = (byte*) outputData.Scan0;

        for (int i = 0; i < height; i++)
        {
            for (int j = 0; j < width; j++)
            {
                HSLColor lowerColor = new HSLColor(lowerPointer[2], lowerPointer[1], lowerPointer[0]);
                HSLColor upperColor = new HSLColor(upperPointer[2], upperPointer[1], upperPointer[0]);
                upperColor.Luminosity = lowerColor.Luminosity;
                Color outputColor = (Color) upperColor;

                outputPointer[0] = outputColor.B;
                outputPointer[1] = outputColor.G;
                outputPointer[2] = outputColor.R;

                // Moving the pointers by 3 bytes per pixel
                lowerPointer += 3;
                upperPointer += 3;
                outputPointer += 3;
            }

            // Moving the pointers to the next pixel row
            lowerPointer += lowerData.Stride - (width * 3);
            upperPointer += upperData.Stride - (width * 3);
            outputPointer += outputData.Stride - (width * 3);
        }
    }

    lower.UnlockBits(lowerData);
    upper.UnlockBits(upperData);
    output.UnlockBits(outputData);

    // Drawing the output image
}