نقل قول:
It really means that 18% of incident light is reflected.
Human perception of brightness is logarithmic, though, and not linear.
Basically, logarithmic means we are multiplying instead of adding.
Compound interest is logarithmic. So is the frequency of the notes on
a piano. So is the decibel scale for measuring sound pressure.
Likewise with the light plotted on a typical histogram.
You can make (or imagine) a set of brightness patches by starting with
100% reflection and halving each time. The next is 50%, then 25%,
12.5%, 6%, 3%, and 1.5%. That's 7 patches. It is a logarithmic
sequence; the factor is 1/2. The first patch is white, the last very
dark gray, virtually black. In the middle it will be middle gray,
12.5% actually, a bit darker than 18% gray.
You can fiddle with sequences like this to make as many patches as you
like, with different gradations of brightness between them. Using a
factor of 0.75, we get 13 steps, with the middle being 18%:
100 75 56 42 32 24 18 13 10 7.5 5.6 4.2 3.2.
ترجمه تحت الفظی: