Hint:

The maximum value of an unsigned 8bit integer is 255. So which value do you get if you calculate 255/256? It is probably not 1 . More like 0.9xxxx  So divide by 255.

Greetings

Normally for [0..1] you'd divide it by 255.

(0..1) ... you mean narrowing the integer range 0..255 down to the interval excluding 0.0 and 1.0 ?

Edit ninja'd ninja'd ... 

I won't

I made my last off by one error just yesterday ;-)

Your secret is safe. 

If unsure, let the compiler figure it out for you ?. Here's two "generic" methods using limits.h:

constexpr auto ucharMax = std::numeric_limits<unsigned char>::max();
float value = pixel / float(ucharMax);
  

float value2 = pixel / float(UCHAR_MAX);

Or you could roll your own for any byte size (which in a general case is overwhelmingly likely but not actually guaranteed to be 8 bits)...

using byte_t = unsigned char;
const byte_t ucharMax = byte_t(0xffffffff); // support any size of uchar up to 64 bits

Or if you know the size of your byte... Use mad hax!