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: Richard Sjolund <email@hidden>
- Date: Fri, 24 Sep 2004 22:12:01 -0500
If the original file from the scanner is a 16 bit file, it means that the
scanner had an analog-to-digital (A/D) converter that took the voltages and
converted them to 65,536 shades of gray. A scanner with an 8-bit A/D
converter converts the same voltages to 256 shades of gray. If there are
only 256 shades of gray in the file, there is no magic (even in Photoshop)
that can get the extra data from the file.
Dick
Wilderness Studio
Solon, Iowa
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From: James Schaefer <email@hidden>
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Date: Fri, 24 Sep 2004 22:20:34 -0400
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To: <email@hidden>
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Subject: 16 bit scan vs. 8 bit scan/16 bit conversion
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If I scan a 4x5 transparency RGB at 2500 dpi and 8 bit color, I get a
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file that is a bit over 300 MB; call it File A.
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If I scan the same transparency at the same dpi, but with 16 bit color,
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I get a file that is twice the size; call it File B.
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If I take the 8-bit File A and convert it in Photoshop to 16 bit color,
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it too is twice the size of A; call this File C.
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I know that File B has more color information in it than File A has.
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What I don't know is whether File C actually has more color information
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than A. I suspect not -- the Second Law must come into play somewhere
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along the line -- but can anyone confirm one way or t'other?
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There is a practical reason for my asking. I shoot panoramas composed
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of multiple overlapping 4x5 images that I assemble by hand in PS to
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produce a final seamless image. I do the assembly with files that are
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300 or 360 dpi and at print-size, up to 22.5 in. high. I print the
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final product on my 7600 at up to the 8-foot-wide limit of the print
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driver. (I don't have a RIP.)
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These panoramas can be up to 10 images wide, which means a lot of image
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manipulation before I get to the final color work. When I got my G4
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three years ago, its 1.5 GB of RAM seemed endless. It isn't. I'd love
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to have a G5 packed with 8 GB, but I don't. Thus, as I assemble these
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pans and they get larger, they get increasingly unwieldy. If I
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assemble them in 8 bit format, they can approach 800 MB in their
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intermediate stages, but if I try to work in 16 bit, they become simply
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gargantuan and completely impractical to work with.
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So here's the question: If I assemble the pans in 8 bit, then convert
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the final flattened image into 16 bit for final color work, have I
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gained anything? (I then return to 8 bit to print and to archive.) Or
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do I retain color headroom only by scanning in 16 bit and keeping the
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file that way until the bitter end?
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Jim Schaefer
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email@hidden
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