One question I get asked a lot by friends and family is "how big can I print this digital photo?" My answer is always "it depends," which then requires a lengthy discussion of pixels per inch and viewing distance and other mundane topics.
So, I put together a little Excel spreadsheet that should help you determine what size prints you can make with reasonable quality based on the size of the digital photos you have. You can get it here or click on the screen capture below (you have to have Microsoft Excel to use the file).
I've based the calculations employed by the spreadsheet largely on my own experience and preferences, so if you have a more or less critical eye than is typical, you might differ with some of the recommendations the guide offers. In that case, leave me a comment and I'll tell you how to change the PPI (pixels per inch) guidelines used in calculating the ratings.
p.s. If anyone wants to help me develop a perl-based version of this so that it can work within a browser, that'd be great.
I would like to help with creating a PHP version of this chart that includes some internationalization. Please mail on interest.
Just one small thing: you should precise on your worksheet that the print size is in inches. This could clear a few misunderstandings. ;-)
Otherwise, good job. I like it.
D'oh! Good catch, guys -- I apologize for not putting a unit on the print size. Those are definitely in inches. I'll work on version 2 of the spreadsheet with both standard inch and cm prints when I get a chance. Thanks again.
One strange thing: on your screen shot, 53dpi is rated as "Fair" while 75 and 109dpi get "Poor". Surely, "fair" should be a higher rating than "poor"...
Surely "fair" should be better than "poor"?
The fact that 53dpi on a 20x30 print is rated as "Fair" while 109dpi on a 11x14 print is rated as "poor" is because *viewing distance* has to be taken into account. You're likely going to be looking at a poster-sized print from a few feet away, whereas an 11x14 print you might view relatively closely (arm's length). Therefore, the pixels on an 11x14 print have to be considerably smaller than those on a poster (just like the "pixels" on a billboard could be a few inches in size and it would still look OK from the highway).
As I said, these are my personal rules of thumb based on printing out lots and lots of digital photos at various sizes, resolutions, DPIs, and using different technologies (dye-sub, inkjet, etc.). Your tastes might differ, but these are the guidelines I use.
It might be a good idea to *link* the point about dependence on viewing distance somewhere on the sheet. Most people will find that confusing I think. Unfortunately I have not found a satisfactory way of explaining printing size without a bit of hand-holding however you do it.
A good friend of mine (hi, Bob!) whipped up a barebones version of the worksheet as a Perl script, so now I have something to muck around with and try to get it into a more friendly and polished tool. I'll post it when it's ready and will definitely try to integrate all these suggestions into the final product. Thanks again.