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Old Dec 30, 2004, 10:02 AM   #1
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I'm attempting to navigate through the morasse of digital camera options, and feeling dead stupid like. I am a digital artist (using scanners as my primary way of inputting paintings into photoshop).I was wondering what the minimum technical specifications are for the following. Photographing paintings so that I can output the digitally modified painting at 300 dpi to a large format digital printer, (i.e. A4/A3/A2).Taking digital photographs so I can blow 'em up to at least A4 and output them on a home inkjet.

Am I right in thinking that 6 megapixels is the minimum megapixels I should be looking at? (obviously quality of lens, etc have a huge impact, but can I get away with getting a lower resolution camera with a better lense)

thanks in advance (also I appologise for the somewhat muddleheaded post xmas typing/sentance construction)

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Old Dec 30, 2004, 11:50 AM   #2
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Unfortunately the question requires a complex answer.

The PPI you get from a scan is different from what you get from a digital camera. This is a good read: http://scantips.com/resolut.html He used a photo taken with a fixed focal length Nikon on a tripod and processed with a Fuji Frontier – considered very good. He could not get scanned detail beyond scanning at 300 PPI.

Most prints are in the 200-250 range. Some people say less. If you are getting 4 X 6 prints from the photofinisher, scanning them and printing at say 8 X 10 you are getting probably around 100 PPI of information. If you scanned the prints at 1200 PPI Photoshop might say you have over 300 PPI for the print. But most of those pixels are just guesses by the scanner of what is between the pixels. You would get about the same results scanning at 300 PPI and then doing an upsample in Photoshop. The end result is still 100 PPI of information in your print, and a shot from a 3Mp camera would be superior. Of course if you get an 8 X 10 from the photofinisher and scan with a good scanner at 300 PPI, you will be able to make an 8 X 10 about as good as the original. Probably better if you are good at Photoshop.

The best A3 print you can get from a 6Mp DSLR camera is about 171 PPI. I've done tests with both of my photo printers and can't see any improvement over around 180PPI with a fairly close inspection with reading glasses (which I don't require for reading). Using an 8X loupe I can see some slight improvement to maybe 240 PPI. Maybe commercial printing could use a little higher, but you get a nice print at 170 PPI.

If you go with an 8Mp prosumer camera rather than a DSLR you will get higher PPIs but a lot more noise and less dynamic range. For an art print noise reduction software like Neat Image or Noise Ninja would be a must. The pro version of Neat Image works as a Photoshop plug-in. I don't think any digital under about $8000 is going to give a really good A2 on close inspection, but you don't tend to view a large print as close as a small one. I have read posts by people who made prints around A2 size from 2Mp cameras and said people thought they were photos. The print was probably behind a desk so people couldn't get very close. I don't like prints from that low a PPI, but it has a lot to do with subject matter, viewing distance and personal standards.

A4 on a home inkjet will give you 175 PPI from a 3.2Mp camera. That actually makes a decent print if you frame so you don't have to crop. I wouldn't consider anything less than 5Mp for what you are doing, and that would give you more pixels than any inkjet can really use for an A4 without cropping.

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Old Dec 30, 2004, 12:01 PM   #3
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Slipe pretty much answers your question but here is another way of looking at it...

Well, let's try to calculate the megapixel requirement (someone correct me if I'm wrong):

A4 paper size = 210mm x 297 mm ~= 8.27 inches x 11.69"

If you need 300dpi, that is a resolution requirement of roughly 2480x3508.

total resolution=2480*3508 ~= 8,700,632

So you need an 8.7 megapixel camera.

I could be wrong but I don't think there are any 8.7 MP prosumer cameras so affordability is going to be a question. I'm not sure about DSLRs though.

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