Re: High Resolution Scans
Re: High Resolution Scans
- Subject: Re: High Resolution Scans
- From: MARK SEGAL <email@hidden>
- Date: Wed, 16 Apr 2008 13:31:47 -0700 (PDT)
I think there may be some lack of clarity here. There is input resolution (the number of pixels per inch created in the imaage file) and output resolution (the number of pixels per inch in the document outputted to the printer). And for sake of further clarity let us call this PPI (pixels per inch) rather than dpi (dots per inch), because dots relates to ink sprayed from inkjet printers (not relevant here), whereas pixels relates to image resolution. Let us assume it is not desired to resample the image for printing. Let us further assume the desired print resolution is 240 PPI, the long dimension of a 35mm size frame is 1.5 inches and the long dimension of the corresponding print will be 9 inches, creating a magnification factor of 6 between the file and the print. The print will have a total of 9*240 pixels on the long dimension = 2160 pixels. This is the total number of pixels which need to be scanned in to the long dimension of the image for this
print size. Therefore the scanner must be set to a PPI setting of 2160 pixels/1.5 inches = 1440 PPI. This of course is a small print size. The same arithmetic applied to a final print size with a long dimension of say 18 inches would need 4320 total pixels at an output resolution of 240 PPI, hence an input resolution from the scanner of 2880 PPI. This all relates to the minimum acceptable resolution of the final OUTPUT (the number of pixels needed to preserve smooth tonal gradations in a print) and has nothing to do with the resolution of the film - another matter. No matter how high or low the resolution of the film, there is a lower limit to the PPI needed for a good print. That is true regardless of the fact that once the print PPI is above a normally accepted quality threshold for the viewing distance, the overall binding constraint on image quality would be the resolution of the film itself. The resolultion of film is not straightforward, because
film grain is clumpy as discussed here http://www.luminous-landscape.com/essays/clumps.shtml,
Mark Segal
----- Original Message ----
From: "email@hidden" <email@hidden>
To: email@hidden
Sent: Wednesday, April 16, 2008 3:32:08 PM
Subject: Re: High Resolution Scans
I worked a number of years ago at a Retouching lab where we output to an
LVT On 32 ISO Slide film. Kodak had us outputting to 1018 DPI. We were
told this was the optimal resolution for the film. I have seen people scan
film at much higher resolutions, but I think you are only piling pixels on
at that point. I mean sure you can scan, with a drum scanner at 5000 dpi,
but if the film is only capable of excepting res 30, I am not sure I see
the point. Just a thought.........
Dan Burbank
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