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#1 Posted : Monday, June 9, 2008 8:20:37 AM(UTC)


Groups: Registered, Tech Support, Administrators
Posts: 764

8bpp (or less than 8) PNG images can have a full alpha channel, but due to the way they are stored, it can be a little bit more difficult to display them in LEADTOOLS.  The main image is still palettized just like a GIF would be.  However, PNGs have another byte array in the file which can give an alpha value for each color in the main palette with values between 0 and 255.  Therefore, if you wanted the alpha value of the 5th color in the palette, you would check the 5th entry in the transparency information.  To get and set this information, you must use L_GetPNGTRNS and L_SETPNGTRNS.  For an example specific to those functions, see:


This example shows how to properly display an 8bpp PNG file with alpha information using L_FeatherAlphaBlendBitmap.  The main difficulty is that you must manually construct the Alpha mask bitmap since L_GetBitmapAlpha only works on 16, 32, and 64 bit images.
File Attachment(s):
API-v15-8bppPNGFeatherAlphaBlend.zip (15kb) downloaded 61 time(s).

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