How do I overlay an image in .NET

Question

I have a .png image i wish to overlay on a base image.

My overlay image contains just a red slant line. I need to get the red line overlayed on the base image at the same co-ordinate as it is in overlay image.

The problem is I do not have the co-ordinates location.

I need to find it programmatically with C#. The overlay image will always be transparent or of white background. What code to find the line co-ordinates from overlay image?

Answer 1

You can create new image, render background image first and then render overlay image over it. Since overlay has alpha channel and line is placed where it should be (i mean there is opaque space on top and left side of line) you do not need coordinates. Illustration code:

Image imageBackground = Image.FromFile("bitmap1.png");
Image imageOverlay = Image.FromFile("bitmap2.png");

Image img = new Bitmap(imageBackground.Width, imageBackground.Height);
using (Graphics gr = Graphics.FromImage(img))
{
    gr.DrawImage(imageBackground, new Point(0, 0));
    gr.DrawImage(imageOverlay, new Point(0, 0));
}
img.Save("output.png", ImageFormat.Png);