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Old Apr 22, 2004, 12:00 PM   #1
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Default scan resolution equivalent to

I'm shopping for a film scanner to convert old pictures to digital and I want a scanner that would give me resolution in the digital file that is equivalent to a 4 megapixel shot, ie I want the same input resolution. The scanner specs for input resolutioon are by dpi, but I don't know how to compare that to megapixels.

Any easy answers?
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Old Apr 22, 2004, 12:35 PM   #2
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Manufacturers often use the terms dpi and ppi interchangeably (even though they are different).

Basically, if you had a 4" x 6" photo and scanned it at 600 dpi, you'd end up with an image size of 1600 x 2400 (3,840,000 pixels). Simply multiple the dpi the scanner is capable of, by the dimensions of the image you are scanning:

4" x 600 = 1600
6" x 600 = 2400

This would be about the same size as an image from a 4 Megapixel Camera (after cropping for the 3:2 aspect ratio of the 4"x6" print).

So, the scan resolution needed will be dependent on both the size of the original images, as well as the optical resolution capability of the scanner.

So, if you are scanning large prints, you can get much higher resolution image output. Or, if you're scanning smaller prints, you'll get less resolution in the output image.

BTW, scanner specs can be "tricky". Make sure you're looking at Optical Resolution (versus "enhanced" or "interpolated" resolution). There can also be a big difference in scanner quality (bit depth, noise, etc.) -- just as there are huge differences between cameras of the same resolution.

Scan speed can also vary dramatically between models.

I'd read reviews for scanners under consideration, and ask for user experiences with them.
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Old Apr 22, 2004, 1:27 PM   #3
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Thanks for the quick reply, and I see what you're saying about the size of the original. Since I'm looking at film scanners the original is the size of a 35mm slide or exposure (i guess roughly 35mm x 48mm?) The plotters I'm looking at are spec'ed at either 3200 dpi or 4000dpi (optical resolution), but the price doubles between the two, so I'm trying to decide what the extra resolution buys me. Using your calculation though :
35mm= about 1.4" X 3200= 4480
48mm= about 1.9" X 3200= 6080
which gives something like 27megapixels! I must be doing something wrong. Could it be dots pe square inch?
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Old Apr 22, 2004, 1:46 PM   #4
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I missed the part about scanning film (versus prints). Most newer film scanners are very high resolution (because you're scanning a very small image size).

I'm no scanner expert, so I'd ask questions about the specific models you are considering here (some of the users here may actually own the scanners you are looking at).

Steve does have a few reviews of older models on this site (see this link):

http://www.steves-digicams.com/digi_....html#scanners

Note that these scanners do produce very high resolution images from film. The Nikon Super Coolscan 4000 ED (4000 dpi) he reviewed produces a 5959 x 3946 pixel image (over 23 Megapixels) from 35mm film.

The Minolta DiMAGE Scan Dual III he reviewed (2820 dpi) produces an image size of 2,688 x 4,032 pixels (over 10 Million Pixels).

Again, there can be a significant difference in quality between models (bit depth, noise, dynamic range), so I'd ask users for opinions on specific models you are considering.
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Old Apr 22, 2004, 3:12 PM   #5
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Quote:
Originally Posted by photophobe
Thanks for the quick reply, and I see what you're saying about the size of the original. Since I'm looking at film scanners the original is the size of a 35mm slide or exposure (i guess roughly 35mm x 48mm?) The plotters I'm looking at are spec'ed at either 3200 dpi or 4000dpi (optical resolution), but the price doubles between the two, so I'm trying to decide what the extra resolution buys me. Using your calculation though :
35mm= about 1.4" X 3200= 4480
48mm= about 1.9" X 3200= 6080
which gives something like 27megapixels! I must be doing something wrong. Could it be dots pe square inch?
Megapixels are a square measurement and dpi is a linear one. Megapixels are expressed as the total area.
DPI is a "per inch" measurement.

A 35mm slide is roughly 1 inch by 1.5 inches. So to get from linear dots per inch to megapixels, which are total dots devided by a million, the calculation is
((1 x 3200) x (1.5 x 3200))/1,000,000
that gives you 15.36 megapixels.

A scan of a 35mm slide at 5000 dpi will give you 37.5 megapixels. People say that scanning photographic film higher than 5000dpi doesn't really give any benefit.
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Old Apr 22, 2004, 3:56 PM   #6
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Thanks, that pretty well answers my question and it looks like $299 for a 3200dpi Minolta Dual Scan would be a good bet for what I want. The Nikon is about double, but probably has better software - these are prices from B&H

Anyway, big thanks, I learned something cool today.
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Old Apr 23, 2004, 7:03 AM   #7
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You might also wish to consider a copier adapter if your camera will take one. I've no direct experience of this.....

Regards,
Graham.
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Old Apr 23, 2004, 8:10 AM   #8
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Another thing to consider is the Digital ICE that comes with that Nikon. I've heard amazing things about the output of that scanner.

Digital ICE - Image Correction & Enhancement.
Digital ICE removes defects or scratches on the surface of the film with out losing any details or any other elements of the original image

(From the B&H description of the "Nikon Super Coolscan 9000 ED, 4000 dpi, Multi-Format, Film Scanner")

Of course, that is a very expensive scanner at almost $2,000. But I've read that Digital ICE has come a long way in the last year or two. So seriously consider some of those features and not just its resolution.

Eric
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Old Apr 23, 2004, 8:10 AM   #9
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I tried a slide copier adapter on a 35mm SLR and it was a waste of time. You need a very bright light source to see the slide and get it in focus. A clear sky works best but then you run into problems of the colour temperature of the light changing during the day and producing a colour cast in the resulting photo. It might work better on a digital camera but I wouldn't hold my breath.
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Old Apr 23, 2004, 6:54 PM   #10
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From what I see of the original poster's targets, I'd suggest the Nikon Coolscan V-ED. This is new-generation, 4000 DPI optical, with digital ICE4 and the "improved negative algorithm" that costs $600 at B&H and Adorama for example.

The main limitation of this in contrast to the next model Nikon 5000 ED seems to be speed and a 14-bit depth (14 * 3 = 42 bits total) while the 5000 has 16-bit depth (48 bits total).

And the contrast between the Nikon 5000 ED and the top model Nikon 9000 ED seems to be size (9000 ED handles medium format) and an "improved rod dispersion LED", and slow speed.

For 35mm, the specs are 38s, 20s, 40s for the V, 5000, and 9000 respectively.

http://www.nikonusa.com/template.php?cat=1&grp=98

The 14 vs 16-bit depth might make a slight difference for slides, but perhaps makes more of a difference for marketing than in practice. The "improved negative handling" is perhaps important -- it does work, and some people have reported a lot of difficulty in scanning negatives in the past (with some having to go to the extreme of scanning as positives, then inverting, then colour correcting).

Digital ICE is also considered a must-have by many -- dust is a big problem with scanning, and manually re-touching makes the processing time even longer; sometimes a fair bit longer (until you get good at it, but ICE is still faster.)

I wouldn't get too excited by the multi-megapixel resolution math. In practice you encounter film limitations (including problems due to handling negatives) that make the effective resolution lower than the figures would suggest.

In particular, film grain is often a problem, especially at high resolutions and for negatives. I've found products such as Neat Image and Noise Ninja to be invaluable for cleaning up images to compete with the output of digital cameras. http://www.neatimage.com

Sharpening is also very useful / important. Focus Magic is a neat tool for this, but IMO is usually not worth the processing time compared to Photoshop's USM. http://www.focusmagic.com

Finally, I've found Wayne Fulton's site to be very helpful for both scanning and for digital camera image processing: http://www.scantips.com/

(I have a Nikon 9000 that I bought from Adorama --- I need to scan medium format.)
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