From: Mats Broberg (mbroberg@swipnet.se)
Date: 04/12/00-10:56:28 AM Z
Gregory Parkinson wrote:
> I've been reading a lot on scanning and one number I've come across
> is that color prints don't give you any better than 200dpi - so scanning
> at a higher resolution is pointless. I supposed if your prints were
> large enough you'd get additional dots in the final scan.
The resolution of a (photographic) color print is the same as the number
of gelatin grains per inch in the emulsion, which exceeds 200 dpi by
many many times. It's true that you don't need them if you don't plan on
blowing up a 6 x 6 neg to wall size, but IF you plan to output a
considerably larger (offset or the equivalent) print than the original,
it is usually better to do most of the blowing up photographically than
on the scanner.
When it comes to scanning color work, it comes down to basically four
important parameters - color depth of the scanner (number of bits per
color), density, resolution and ratio between the original and the final
size of image. If you aim to print a colour image with a 150 lpi screen,
there's no use to scan it in any higher resolution than perhaps 375 dpi
since the additional information won't add quality to the final image.
However, this is only valid if the ratio between the original and the
screened print is 1:1. If the original is smaller in size than the print
the resolution I mentioned above needs to be multiplied with the number
of times the print is larger than the original.
Desktop scanners have come along way and it is impressive what you can
get for that little money. But I wouldn't be overly enthusiastic anyway.
The color depth is usually 36 bits, the OPTICAL resolution is most often
only 600 x 1200 dpi and the density somewhere around 3.2 or so. If you
look at drum scanners or the v.v.v.best flatbed scanners (e.g.
Linotype-Hell) you will find that that color depth, optical resolution
and density is far greater, which shows in the final prints.
By the way, OPTICAL resolution is what counts, so don't fool yourself
when scanner manufacturers brag about 2400 x 2400 dpi, 9600 x 9600 dpi
and stuff like that. If they do they are referring to software
interpolated resolution and not optical resolution and software
interpolation is only mathematics, and nothing else. What it does is it
guesses by advanced calculations what the areas in the optically
recorded pixel would look like if that pixel was split into 4 pixels, 9
pixels, 16 pixels etc. That does not mean it actually records any new
information from the original. Avoid using software interpolated resolution.
Mats Brobergs
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