Re: 16 bit scan vs. 8 bit scan/16 bit conversion
Re: 16 bit scan vs. 8 bit scan/16 bit conversion
- Subject: Re: 16 bit scan vs. 8 bit scan/16 bit conversion
- From: David Scharf <email@hidden>
- Date: Fri, 24 Sep 2004 20:14:06 -0700
DAVID SCHARF PHOTOGRAPHY
Scanning Electron Microscopy
Phone 323-666-8657
Fax 323-666-0449
2100 Loma Vista Place
Los Angeles, CA 90039
http://www.scharfphoto.com
http://www.soquelec.com/dscharf/images.htm
Hi James,
Here's what I think:
Dave Scharf
_________________________________________________
James Schaefer wrote:
If I scan a 4x5 transparency RGB at 2500 dpi and 8 bit
color, I get a file that is a bit over 300 MB; call it File A.
If I scan the same transparency at the same dpi, but with 16 bit color,
I get a file that is twice the size; call it File B.
If I take the 8-bit File A and convert it in Photoshop to 16 bit color,
it too is twice the size of A; call this File C.
I know that File B has more color information in it than File A has.
What I don't know is whether File C actually has more color information
than A. I suspect not -- the Second Law must come into play somewhere
along the line -- but can anyone confirm one way or t'other?
File C does not have more information.
There is a practical reason for my asking. I shoot panoramas composed
of multiple overlapping 4x5 images that I assemble by hand in PS to
produce a final seamless image. I do the assembly with files that are
300 or 360 dpi and at print-size, up to 22.5 in. high. I print the
final product on my 7600 at up to the 8-foot-wide limit of the print
driver. (I don't have a RIP.)
These panoramas can be up to 10 images wide, which means a lot of image
manipulation before I get to the final color work. When I got my G4
three years ago, its 1.5 GB of RAM seemed endless. It isn't. I'd love
to have a G5 packed with 8 GB, but I don't. Thus, as I assemble these
pans and they get larger, they get increasingly unwieldy. If I
assemble them in 8 bit format, they can approach 800 MB in their
intermediate stages, but if I try to work in 16 bit, they become simply
gargantuan and completely impractical to work with.
Why don't you scan in 16 bit do your processing, then convert to 8 bit.
After you have done this with each image, then join them together. You
must, however do the exact same processing to each image.
Then save your money for a G5 and a terabyte HD.
So here's the question: If I assemble the pans in 8 bit, then convert
the final flattened image into 16 bit for final color work, have I
gained anything? (I then return to 8 bit to print and to archive.) Or
do I retain color headroom only by scanning in 16 bit and keeping the
file that way until the bitter end?
The only thing you may gain by converting your 8 bit to 16 bit is
possibly (depending on if you leave shadow and highlight headroom) some
elbow room for processing so that you don't clip.
Jim Schaefer
email@hidden
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