Much beyond 8-bit per channel is rare.  8-bit gives you 2^(83) or 2^(24) or 16777216 individual colors plus 256 alpha grey-levels.  At 16-bit per channel, you're talking 281474976710656 (281 trillion colors - way, way, way far beyond the human eye's ability to distinguish) individual colors with 65536 alpha grey-levels.  The numbers at 64-bit per channel might not even be printable here.  Just think about a 2^(643) or 2^(192) number of colors.  That is a 6 with 57 zeroes after it.

Are you sure you are not confusing image bits-per-pixel with 32-bit vs. 64-bit OS/addressing/size schemes?

C makes it easy to shoot yourself in the foot. C++ makes it harder, but when you do, you blow your whole leg off.

 -- Bjarne Stroustrup

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