Luminous Landscape Forum
Raw & Post Processing, Printing => Digital Image Processing => Topic started by: Edalongthepacific on February 10, 2011, 05:36:31 pm
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As a scale of recommended DPI (or PPI if you wish) for scanning, how could the attached illustration be improved?
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Scanning at 360 for high quality inkjet printing isn't going to get you there. Think about it for a second. If you've got a frame of 1x1.5" film, scan it at 360 ppi then print it at 360 ppi, how bit is your print going to be?
For scanning film with the intent of printing you want to scan at the highest optical resolution of the scanner. So if the scanner has a resolution of 4800 ppi, scan at that. Other than that, I think you're making it much more difficult than it needs to be. Documents/photo prints scanned at 200 to 300 ppi will be fine. Much lower than that and they're not going to be much good for anything. Higher than that is overkill.
What are the column headings supposed to represent? I don't understand the association of 48 bit ProPhoto with rare documents.
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Yes, thank you, I omitted film from this chart. I believe (right or wrong) that rare documents should be scanned at 600 DPI and saved in a ProPhoto color space. This would be a large file but good as an archive...Yes?
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Yes, thank you, I omitted film from this chart.
You could add an output magnification factor (a simple multiplication factor) to deal with that.
I believe (right or wrong) that rare documents should be scanned at 600 DPI and saved in a ProPhoto color space. This would be a large file but good as an archive...Yes?
Your criteria only account for theoretical resolution requirements. What is omitted is that a scanner has a native resolution. Using lower resolutions tends to introduce increased (aliasing) artifacts. The aliasing will exaggerate fine detail transitions, e.g. paper structure or sharp edges leading to stairstepping artifacts. From a quality perspective the best results are to be had from scanning at the native scanner resolution, and downsampling with a good resampling method. All other methods will result in sub-optimal results, although for some less critical uses they may be good enough.
Sometimes speed is more important than quality, in which case all bets are off. A compromise can be used in these cases, e.g. scan at twice the required resolution, and downsample to 50%. That will give the best of both worlds.
The required resolution is always a function of the intended end use.
Cheers,
Bart
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Good point. Native resolution is important but the chart is a guide rather than a rule. See updated version.
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It could be somewhat improved by correctly spelling jpeg ;)
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Yes! It is: JPEG (J-PEG), pardon my dyslexia. I believe the latest version (attached) is more accurate, simpler and more completely illustrative of bit depth and DPI (or PPI as it should be except for scanners or whatever).