GDI+: Set all pixels to given color while retaining existing alpha value

Question

What is the best way to set the RGB components of every pixel in a System.Drawing.Bitmap to a single, solid color? If possible, I\'d like to avoid manually loop

Answer 1

I know this is already answered, but based on Hans Passant's answer the resulting code looks something like this:

public class Recolor
{
    public static Bitmap Tint(string filePath, Color c)
    {
        // load from file
        Image original = Image.FromFile(filePath);
        original = new Bitmap(original);

        //get a graphics object from the new image
        Graphics g = Graphics.FromImage(original);

        //create the ColorMatrix
        ColorMatrix colorMatrix = new ColorMatrix(
            new float[][]{
                    new float[] {0, 0, 0, 0, 0},
                    new float[] {0, 0, 0, 0, 0},
                    new float[] {0, 0, 0, 0, 0},
                    new float[] {0, 0, 0, 1, 0},
                    new float[] {c.R / 255.0f,
                                 c.G / 255.0f,
                                 c.B / 255.0f,
                                 0, 1}
                });

        //create some image attributes
        ImageAttributes attributes = new ImageAttributes();

        //set the color matrix attribute
        attributes.SetColorMatrix(colorMatrix);

        //draw the original image on the new image
        //using the color matrix
        g.DrawImage(original, 
            new Rectangle(0, 0, original.Width, original.Height),
            0, 0, original.Width, original.Height,
            GraphicsUnit.Pixel, attributes);

        //dispose the Graphics object
        g.Dispose();

        //return a bitmap
        return (Bitmap)original;
    }
}

Download a working demo here: http://benpowell.org/change-the-color-of-a-transparent-png-image-icon-on-the-fly-using-asp-net-mvc/