Raw have a higher bit-depth and
greater color space, but why should 4.
trillion colors matter when the human eye is
only capable of discerning about 10 million
different colors?
The extra color information becomes
crucial when we begin making tonal edits.
By boosting contrast or adjusting tones, we
squeeze the existing color information; with
a narrower color space, this means a greater
chance of image degradation. This often
takes the form of ugly color banding in areas
of tonal gradation like smooth skies, as you
can see in the edited JPEG here. Images with a
higher bit-depth have less chance of banding.
Raws and
TIFF files are
lossless formats: no
matter how many
times you open and
close them, they
never deteriorate.
By contrast, JPEG
is a lossy format.
Every time a JPEG is
opened, its data is
uncompressed, then
compressed again
on closing, which
affects image quality.
This JPEG has been
opened and closed
50 times, and the
result is a mess.