Convert a Color Image into Grayscale

First create a new C# Windows Form Application, Add two picture boxes and a button. (I am using default names of the controls.)

Set an image for the first Picture Box (pictureBox1)

Add the following code to the button click event.

Bitmap bitmap1 = new Bitmap(pictureBox1.Image);

int width1 = bitmap1.Width;
int height1 = bitmap1.Height;

Bitmap bitmap2 = new Bitmap(width1, height1);

for (int i = 0; i < width1; i++)
{
    for (int j = 0; j < height1; j++)
    {
	Color color1 = bitmap1.GetPixel(i, j);

	byte R = color1.R;
	byte G = color1.G;
	byte B = color1.B;

	int common = (R + G + B) / 3;

	color1 = Color.FromArgb(common, common, common);

	bitmap2.SetPixel(i, j, color1);
    }
}

pictureBox2.Image = bitmap2;