You can implement transparency when doing any of the following:
Once a region is defined, you can create a mask from it, using the CreateMaskFromRegion method, which you can save in the alpha channel of a 16-bit or 32-bit file. Refer to the SetAlphaImage method for an example of how to save a region in an alpha channel. When specifying a transparent color, you can use the Windows PALETTEINDEX macro to refer to a particular palette index (where the RasterColor value is >= 0x01000000). Using a palette index for transparency means that one of the remaining colors in the palette can have the same RGB value as the transparent color, without being interpreted as transparent.
Medical Web Viewer .NET