The color components computation had intermediate results that could overflow
a signed int. So now the computation is done using unsigned int instead, which
prevents the overflow (since the max intermediate value is 255*255*257*257,
which fits in an unsigned int).
Note: I also considered adding an explicit cast to do the uint8 * uint8
operations using uint32, but decided not to as it is not required (there is no
overflow due to integer promotion) and makes the code more difficult to read.
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