replace color in an image in c#

Question

What is the way in C# to replace a color for some parts of an image without affecting its texture?

You can see good example of the result here
Thanks

Answer 1

One way to efficiently replace a color is to use a remap table. In the following example, an image is drawn inside a picture box. In the Paint event, the color Color.Black is changed to Color.Blue:

private void pictureBox_Paint(object sender, PaintEventArgs e)
{
    Graphics g = e.Graphics;
    using (Bitmap bmp = new Bitmap("myImage.png"))
    {

        // Set the image attribute's color mappings
        ColorMap[] colorMap = new ColorMap[1];
        colorMap[0] = new ColorMap();
        colorMap[0].OldColor = Color.Black;
        colorMap[0].NewColor = Color.Blue;
        ImageAttributes attr = new ImageAttributes();
        attr.SetRemapTable(colorMap);
        // Draw using the color map
        Rectangle rect = new Rectangle(0, 0, bmp.Width, bmp.Height);
        g.DrawImage(bmp, rect, 0, 0, rect.Width, rect.Height, GraphicsUnit.Pixel, attr);
    }
}

More information: http://msdn.microsoft.com/en-us/library/4b4dc1kz%28v=vs.110%29.aspx

Answer 2

Upon doing research i found no efficient/smoothe way of doing this, so i dont it myself, the code could be cleaned up ALOT but it gets the job done, its not efficient but it is smoother and allows you to set a tolerance.

public static Image ColorReplace(this Image inputImage, int tolerance, Color oldColor, Color NewColor)
    {
        Bitmap outputImage = new Bitmap(inputImage.Width, inputImage.Height);
        Graphics G = Graphics.FromImage(outputImage);
        G.DrawImage(inputImage, 0, 0);
        for (Int32 y = 0; y < outputImage.Height; y++)
            for (Int32 x = 0; x < outputImage.Width; x++)
            {
                Color PixelColor = outputImage.GetPixel(x, y);
                if (PixelColor.R > oldColor.R - tolerance && PixelColor.R < oldColor.R + tolerance && PixelColor.G > oldColor.G - tolerance && PixelColor.G < oldColor.G + tolerance && PixelColor.B > oldColor.B - tolerance && PixelColor.B < oldColor.B + tolerance)
                {
                    int RColorDiff = oldColor.R - PixelColor.R;
                    int GColorDiff = oldColor.G - PixelColor.G;
                    int BColorDiff = oldColor.B - PixelColor.B;

                    if (PixelColor.R > oldColor.R) RColorDiff = NewColor.R + RColorDiff;
                    else RColorDiff = NewColor.R - RColorDiff;
                    if (RColorDiff > 255) RColorDiff = 255;
                    if (RColorDiff < 0) RColorDiff = 0;
                    if (PixelColor.G > oldColor.G) GColorDiff = NewColor.G + GColorDiff;
                    else GColorDiff = NewColor.G - GColorDiff;
                    if (GColorDiff > 255) GColorDiff = 255;
                    if (GColorDiff < 0) GColorDiff = 0;
                    if (PixelColor.B > oldColor.B) BColorDiff = NewColor.B + BColorDiff;
                    else BColorDiff = NewColor.B - BColorDiff;
                    if (BColorDiff > 255) BColorDiff = 255;
                    if (BColorDiff < 0) BColorDiff = 0;

                    outputImage.SetPixel(x, y, Color.FromArgb(RColorDiff, GColorDiff, BColorDiff));
                }
            }
        return outputImage;
    }

Answer 3

try this:

Color color = Color.Black; //Your desired colour

byte r = color.R; //For Red colour

Bitmap bmp = new Bitmap(this.BackgroundImage);
for (int x = 0; x < bmp.Width; x++)
{
    for (int y = 0; y < bmp.Height; y++)
    {
        Color gotColor = bmp.GetPixel(x, y);
        gotColor = Color.FromArgb(r, gotColor.G, gotColor.B);
        bmp.SetPixel(x, y, gotColor);
    }
}

Answer 4

Found the way to do that, this requires RGB<->HSL conversions (good class for HSL color can be found here)
1. Get a reference value (in hsl) representing the color you want to replace
2. Get the hsl value for your target color
3. Get image pixels and for each pixel:
4. calculate the hsl value of the pixel, and replace it with (pixelHsl / refHsl) * targetHsl

This did the job for me, thanks for all who helped