How to add outlines to transparent images?

Question

I am trying to create a feature where I could apply a stroke effect (similar to how Photoshop does it) to my images.

I have scoured the inte.net, but have not been able to find a proper solution. How would one approach create such a feature?

I want to use the alpha channel as the source for the outline. Something like this:

I know there are solutions that use dilate method. But to be honest, I don't really know much about that.

Is there some algorithm that can be used in creating a such outline? Would appreciate any help

Answer 1

A way to add outlines to transparent images is to use the Image. Clone method to create a copy of the original image and then use the Graphics.DrawImage method to draw the outline.

using (var bitmap = (Bitmap)originalImage.Clone())
using (var graphics = Graphics.FromImage(bitmap))
{
    var pen = new Pen(Color.Black, 2);
    graphics.DrawImage(originalImage, new Rectangle(0, 0, bitmap.Width, bitmap.Height), 0, 0, bitmap.Width, bitmap.Height, GraphicsUnit.Pixel, imageAttributes);
}

The above will create an outline of width 2 and the color black.

Note : the above code assumes that you have already loaded an image into a Bitmap object called "originalImage". Also, the Graphics. The DrawImage method will keep the transparency of the image.

This is one way. HTH Pablo