Re: 16 bits = 15 bits in Photoshop?
Re: 16 bits = 15 bits in Photoshop?
- Subject: Re: 16 bits = 15 bits in Photoshop?
- From: Robert L Krawitz <email@hidden>
- Date: Wed, 13 Apr 2005 18:59:19 -0400
Date: Wed, 13 Apr 2005 21:28:32 +0100
From: Martin Orpen <email@hidden>
on 13/4/05 21:01, Marco Ugolini at email@hidden wrote:
> To get back to the substance, it is obvious why Photoshop needs a 16 bit
> architecture to display the 15 bits it uses in its files, but still the
> question remains unanswered: why is Photoshop using 15 bits, and not 16? Why
> stop at 15 and not go all the way?
>
> I hope someone can clear that one for me. Thank you.
I already told you - because it's practical.
Photoshop has to be able to run on some old hardware that is going to be
screwed by huge numbers of 16-bit calculations.
Working with 32769 levels is a whole lot quicker than 65536 and having an
integer at the half way mark rather than a decimal also makes the maths
easier.
I don't see how working with 32769 levels is a lot quicker than 65536
in general. If you have a dense lookup table and a small cache you
might get some improvement from the smaller table, but the
arithmetic's no faster.
Computers normally do arithmetic in 8, 16, 32, or 64 bit chunks. It's
no faster working on a 15-bit quantity than a 16-bit quantity. If
they want to be able to detect overflows in some cases I can see the
point, but it seems very strange.
--
Robert Krawitz <email@hidden>
Tall Clubs International -- http://www.tall.org/ or 1-888-IM-TALL-2
Member of the League for Programming Freedom -- mail email@hidden
Project lead for Gimp Print -- http://gimp-print.sourceforge.net
"Linux doesn't dictate how I work, I dictate how Linux works."
--Eric Crampton
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