Re: [Gimp-user] 8 bit vs. 16 or more bit

[Kevin Brubeck Unhammer <unhammer fsfe org>]

Alexandre Prokoudine <alexandre prokoudine gmail com> writes:

> On Mon, Dec 19, 2011 at 8:06 PM, Kevin Horkan wrote:
> > I've tried some research on this subject but have come up with little
> > definitive information.  I'm new to gimp, have used photoshop some,
> > and am new to the iMac and OSx operating system.  As a
> > photographer moving from prosumer to professional (hopefully), I am
> > wondering about the quality differences between gimp and photoshop,
> > especially in the bit rate area.
>
> Photoshop wins right now

But Darktable (http://darktable.sf.net/) runs on Mac, right? I highly
recommend using Darktable for RAW editing (especially things that have
to do with color/exposure changes), then opening in GIMP for
transformations and touch-up. 

I'm no expert, but the way I understand it:

If you're producing for screen/web at least, 8 bit vs 16 bit doesn't
matter for a static image in itself, since what you see on the screen is
no more than 8 bit anyway. Where it matters is in the editing process,
since certain operations (e.g. color curve changes) can lead to minor
"rounding errors". 16 bits means you have more numbers of each color,
similar to having more decimal places. E.g. if you don't know how to
deal with decimal points, and you do one operation that divides by 3 and
then times 2,

    10 / 3 = 3.333… ≃ 3,
    3 * 2 = 6

while if you keep one decimal until you're done calculating,

    10 / 3 = 3.333… ≃ 3.3,
    3.3 * 2 = 6.6,
    (and now we're done calculating, round off the last digit:)
    6.6 ≃ 7

And that kind of rounding can add up.

The picture in
http://www.microstockgroup.com/photoshop-discussion/8-bit-or-16-bit/
gives an example of an image edited once in 8 bit and once in 16 bit
which was then converted to 8 bit.


HTH,
Kevin Brubeck Unhammer