How to determine the transparency color of a bitmap

I know you can programmatically determine the tranparency c开发者_如何转开发olor of a .gif

Is there a way to do the same for a Bitmap?

Right now, I am doing this heuristically by sampling around the outer edge but of course this is not 100% reliable.

I don't believe the BMP file format supports the concept of transparency. My understanding is that if BMP images are used with transparency, it's using an application-defined colour, like RGB(255,0,255) to specify transparent areas.

What you may do is:

• To sample the occluded image.
• Apply canny edge detection algorithm to detect outer edges of the object in your bitmap image.
• You can be approximate, you may also need to tweak a bit to get only the outer edges.
• Then you can perform an intersection of these 2 samples to get the occluded image, across the bitmap image edges.
• By now, you will be having 2 images. Make sure the occlusion-extracted image is transparent and on top.
• Just put the original bitmap beneath the extracted image and you'll achieve transparency with your bitmap image too! :)