Re: 16 bit versus 8bit
Re: 16 bit versus 8bit
- Subject: Re: 16 bit versus 8bit
- From: "Tim Mimpriss" <email@hidden>
- Date: Thu, 7 Feb 2002 16:29:11 -0000
In reply to LeeVaris, Bruce Fraser wrote:
<<
Gaps in histograms don't necessarily
indicate a problem. They do, however, indicate a potential problem
should you need to further differentiate the tones on each side of
the gap. You'll have a lot more freedom to do so without introducing
posterization and banding if you have some data inbetween than if you
don't. That's really all the histogram tells you.
>
>
My guess is that most of us see smooth tonal gradation with as few as 128
evenly spaced levels between black and white, so in most real world
situations it is going to be rather difficult to prove to the sceptic that
16 bit editing is superior to 8 bit. Whether there are actually 16 bits
worth of data in the file, or merely 10 or 12, is not the issue. The ability
to reduce rounding errors of successive tonal moves is.
In a highly contrived test it is easy enough to show that 16 bit editing can
preserve detail which would be lost in 8 bit mode. Make a 8 bit, grayscale
mode gradient from black to white using PhotoShop's gradient tool, and make
a copy. Convert the copy to 16 bit mode: it still has only 256 levels, of
course. Now change the gamma of each file, first to 0.5 with a Levels
adjustment, and then to 2.0 with another Levels adjustment. The 8 bit file
now shows significant posterizing both on screen and on print, but the 16
bit file doesn't, even though, in this case, it started with the same 8 bit
data.
This suggests to me that it is better to use 16 bit data and 16 bit mode
editing while making significant tonal moves (gamma, levels, curves, color
adjustments). And if, like me, import essentially raw image data from the
scanner and do all the adjustments in PS, it is doubly important to start
with high bit data. If later I need to re-purpose my 8 bit final, saved
file, I still have some scope for enhancements without wrecking the image.
Tim Mimpriss
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