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I have searched the web (via Google) for examples on how to convert a GIF image
into a transparent GIF image without much success. What I wanted was there,
just not in the way I wanted it.
Some of the methods I've seen on the web that converts a non-transparent GIF to
a transparent GIF used unsafe code to perform the conversions. With luck, I
stumbled across a couple of examples that performed the conversion without
unsafe code, and I ran into Bob
Powell's transparency page and voila, found what I was looking for.
Although what I was looking for was there, it was mixed in with the UI code and
not put together in a way I could understand. So I took Bob's code, moved the
code that did the conversion into it's own class, put some extra comments in
there, re-formatted the code, and changed some variable names.
Using the code
The GifConverter class contains a single public shared method,
GetTransparentGif. This class takes two arguments, Image (Bitmap) and
TransparentColor (Color). The Image argument is the image to be converted. The
original image is not touched, instead the image is "copied" to a new image
that the method returns. The TransparentColor argument is the color within the
palette that will be set as the color to make transparent. There are currently
no checks within the method to verify the source image is a GIF image.
Points of Interest
Instead of using unsafe code to perform the copy, this library uses the
System.Runtime.Marshal class to perform bit-by-bit reading/writing to
effectively copy the source bitmap's data to the destination bitmap.
I learned a lot rewriting the original by Bob Powell into a usable
v1.0 Initial Release
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My favorite development projects include developing the Windows Form Controls and Web Controls in .Net. Primarily, the design-time classes (Designer and TypeConverters) for controls and classes, and GDI+.