Number of pixels levels of 16 bit Grayscale scans

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Posted By
Chris_D_Johnson_1122
Jan 19, 2007
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372
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4
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Closed
I’m looking for a answer to what is probably an obvious question.

I understand the importance of acquiring as many pixel levels as possible when I scan, and shooting in raw format; to provide headroom in editing for example.

My question is, how many pixel levels result when I scan my black and white negative in 16 bit grayscale mode?

Presumably an 8 bit scan would result in 256 pixel levels and, the logic would be, that a 16 scan would result in a file with 65,536 levels of tone in one grayscale channel. Is this correct?

And, if the answer is not specifically 65,536, the gist of my question is, how many more than 256 levels are there.

Also, does it follow that when I do scan a color neg in 48 bit RGB, I’m ending up with trillions of pixels levels?

Note that I’m not primarily asking about what would happen if I scan my black and white negative as if it were a color negative and used the 48 bit RGB mode. I’m strictly asking about what results when the scanner interface is set to 16 bit grayscale mode.

The question I’m asking is not specific to any particular scanner but, if it helps, I’m using Silverfast Ai Studio with an Epson 4990 scanner.

Thanks,
Chris
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16-bit bit grayscale level number pixel scan

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TT
Toby_Thain
Jan 19, 2007
Yes… up to 2^16 (65536). But of course your scanner probably does not really have 16 bit precision.
AR
alan_ruta
Jan 20, 2007
I’m not sure of the exact number when its 48bit. It might be 2^16 * 2^16 * 2^16. If its not trillions its alot.

While it may not be that less is more, more may not be all that much, depending on the image. 16 bits per channel of a sunset might not look much different than 8. IMHO there are at least 3 important factors.
1. the d-max (density range) of the scanner. 64 bits per channel won’t help if the scanner doesn’t recognize nuances in the dark shadows or specular highlight areas.
2. How well the scanner or photoshop or some other software compression from 16 to 8 bit. Since many rips handle 8 bit, image data must be discarded.
3. If the files are to be screen printed, many CTP setters have limits. If the imager has a dpi of 2400 (pretty standard though many do 3600) at 2400dpi a 200ls will yield a maximum of 144 shades of gray (much less than the 256 that 8 bit does) so 16 bit can be overkill.

alan
B
Bernie
Jan 20, 2007
There were some old threads on 16-bit mode where IIRC, Chris Cox said that for a variety of reasons, 16-bit channels actually had 2^15+1 bits (32769 bits)

this is in Photoshop, what your scanner hardware/software does is a whole other matter
TT
Toby_Thain
Jan 21, 2007
alan – any imagesetter/platesetter using stochastic screening is effectively continuous tone, so 16 bit would be a win (assuming the whole pipeline transports the deep data).

Nomad – yes, Photoshop drops one bit, and works with 2^15+1 representable levels. In most photographic or scanned images this isn’t a problem because the original data has less precision anyway.

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