From time to time we peruse the internet to see what curious information about digital files and media might be in circulation. When we can, we like supporting artists at risk so occasionally we respond to a plea for help. Just last week we attempted to assist a woman via her entry on an artists' forum. Let's call this woman Penelope. She wanted to know about making a print from a digital file of her painting. She took a picture with an entry level digital SLR camera of her original art (size 12" x 14"). She saw that the raw image size was 60" x 40" once she downloaded the file to her computer. Based on this observation she wanted to know if she could reproduce small artwork as much larger prints. We went to work setting her straight about pixels and print size.
Our response went something like this:
Digital cameras can be a little deceiving when dealing with print quality. Although the size says 60"x40," that is only giving you a very small part of the information you need. What is more important than the size is the DPI or pixel count. Almost all digital cameras create a file that is 72dpi. You say your file is 40x60, so your file is 2880x4320 pixels. If you print this file using 72 pixels for every inch of the print you will get a 40x60 print. Unfortunately 72 pixels for each inch is not good print quality to put it mildly. You actually need about 300 pixels for each inch to make the image look good.
If you open your file in Gimp or Photoshop or another image editing software and go under file/resize or file/image size, you will find all of your pixel, dpi and size information. If you uncheck "resample" in this window you will be able to change your DPI setting without changing the number of pixels in your file. This is very important because your prints are only as good as the pixels that the camera originally made. We did this in Photoshop and changed our dpi setting to 300. This gives you a good print size of 9.6" x 14.4" Since your 12x14 size is not the same proportion as your camera, you probably have to crop a bit which is going to decrease your pixels a bit also. So if you crop to 12x14, that gives you a resolution of 240dpi, which is still reasonable for printing. All in all, you can print up to about 14" wide with good quality from your camera.
Photographing art is much different than photographing reality because art has much more fine detail so there really isn't much flexibility to print larger. If you plan to sell prints, I would strongly suggest finding an art reproduction studio with a Betterlight scanner. These scanners give much more resolution in terms of file size and make for a much higher quality print.