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Old Oct 9, 2003, 2:10 PM   #1
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I got a scanner that scans optically at 2400x2400. I would like to scan a few pics and possibly one day i might print them out. When I scan them I can pick the DPI I would like to choose. I know at 72dpi would be fine for viewing on a monitor. My question would be what would be a good dpi to select to scan so i could possibly edit and reprint one day, 300dpi, 600, 1200 2400, etc.
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Old Oct 9, 2003, 4:43 PM   #2
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Read this and go on to the next page where he runs tests with an image taken with a fixed focal length Nikon on a tripod. The upshot is that you are spinning your wheels over 300PPI. You just get a large file with no extra detail. http://www.scantips.com/basics08.html
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Old Oct 9, 2003, 6:38 PM   #3
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Depends on what you're scanning...if you're going to print the same size as your source you are, but if you're scanning a slide (or anything else you want to blow up) you need those higher resolutions (I didn't bother reading the article so I don't know if they said that, I just know from more than a decade of scanning experience).
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Old Oct 9, 2003, 7:52 PM   #4
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thanks for the info guys. I kinda figured that scanning a 4x6 over 300dpi would be a waste unless you want to enlarge it. You should scan 35mm film at higher dpi since it is getting enlarged many times, like mike said.
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Old Oct 9, 2003, 8:40 PM   #5
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Well you said you wanted to scan pictures. The article specifically says the 300PPI refers to your question about scanning photos and that slides and negatives are a completely different thing. I think someone should read the referenced material before disagreeing with it.

The post is wrong about the 300PPI not applying to “anything else you want to blow up”. You get all of the information available from a very good print scanning at 300PPI, and the resolution is smaller than that for most prints. There is no reason to scan or archive at higher than that. The scan takes forever and it gobbles space and RAM to work with it. When you are ready to print upsample the image – that is effectively all the scanner is doing. An exception might be for someone who is going to print a large photo quality blow-up directly from the scan – but few people are willing to spend the money for ink and paper without first taking it through some tweaking.

You can get improvements in film and slides up to at least 4000PPI and probably higher.
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Old Oct 9, 2003, 9:29 PM   #6
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600 dpi if you're going to enlarge them much. Otherwise, 300 dpi, good for archive.
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Old Oct 10, 2003, 2:45 AM   #7
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The real question is what scanner dpi is necessary to get the maximum information from the print. It then doesn't matter what size you blow it up to - it'll be as good as you can possibly get from that print.

It's easy to do the experiment for yourself. Scan a nice sharp print at 300dpi and at 400 dpi, display enlarged versions alongside each other, and see if you can see the difference. I have on occasions persuaded myself that I can get a better result at slightly higher than 300dpi, and 400dpi is definitely overkill.

So I generally use 350dpi myself.
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Old Oct 10, 2003, 9:41 AM   #8
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When scanning old black and white pics I have had the best results at 150 to 200 dpi. Color prints I use 300 dpi.
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Old Oct 10, 2003, 11:57 AM   #9
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Scanners and printers have one thing in common. The data specs might produce X dots per inch, but that doesn't necessarily mean that's the 'sweet spot' in the optical path for translated resolution, or inkjet transfer. And of course with printers of the inkjet type, ink bleed due to incompatible paper and ink can make your 300dpi spec look more like a repeatable 200dpi! Still you can be easily fooled by resolution enhancement - or artificial edge sharpening. VOX
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Old Oct 10, 2003, 1:59 PM   #10
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Quote:
Originally Posted by voxmagna
Scanners and printers have one thing in common. The data specs might produce X dots per inch, but that doesn't necessarily mean that's the 'sweet spot' in the optical path for translated resolution, or inkjet transfer. And of course with printers of the inkjet type, ink bleed due to incompatible paper and ink can make your 300dpi spec look more like a repeatable 200dpi! Still you can be easily fooled by resolution enhancement - or artificial edge sharpening. VOX
Back when scanners had 300PPI optical the “sweet spot” was significant. Even with 600PPI people still felt there was an advantage to scanning at an even divisor of the resolution. But with the number of CCDs on a 2400 PPI scanner and the more sophisticated algorithms there isn’t really a sweet spot from what I read. Of course everything you read isn’t necessarily correct.

As I understand the sweet spot theory on a printer you want to send the image at the resolution that is going to be used so the spooler doesn’t have to resample. That of course is impossible on printers with say 720 X 1440 as something has to be interpolated. It might be true for a 1200 X 1200 or 2400 X 2400 but I have read varying theories. So for a 6 color photo printer there are 6 dots to try to represent a pixel, so 2400DPI divided by 6 would give a scan of 400 PPI to keep the printer from interpolating. If you scan a 4 X 6 print and set the scanner for an 8 X 10 with 400PPI output it would actually scan at 800 PPI after the excess was trimmed from the ends to keep the proportions.

But I have read from seemingly reliable sources that the spooler algorithm is so complex that you are rebuilding the image regardless of input resolution so you are effectively interpolating every image anyway. I have also read that some inkjets use more than 6 dots to represent a pixel with numbers as high as 14 per pixel, so a 2400DPI printer would need a scan of say 171.14PPI to avoid interpolation. I have no idea other than to say that I see no improvement in printed quality scanning a photo over 300PPI regardless of print size. The printer spooler seems to be able to guess the extra pixels as well as the scanner. And I have a good 2400PPI wide carriage photo printer. I use my film scanner when I can locate the negatives so my experience scanning small photos and printing them larger is limited. I would like to see a white paper on the subject from one of the printer manufacturers.
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