how can I create the 32bpp images? (I need an additional alpha channel for the fuzzy edges of icons). Do I have to use Photoshop (or else) to create the toolbar icons?
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Yes. Getting the final 32-bit RGBA bitmap can be tricky. One
way to do it is to export the image as PNG, then open with Microsoft
Paint, finally, save as “24-bit Bitmap”, which will save a 32-bit
bitmap with the alpha channel preserved.

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