Stephen A. asked a question this morning, how many pixels are needed to get a good large print. My assumption is that he means from a photo printing shop, not from his home inkjet printer.
I’ve had this chart for a while, though I don’t remember where I got it from — probably either SmugMug, Digital Grin, EZ Prints or RitzPix. If you work with a photo-printing house and have better info, please let us know.
| Print size(in.) | Min. width(pixels) | Min. height(pixels) |
| 4×6 | 800 | 600 |
| 5×7 | 1050 | 750 |
| 8×10 | 1536 | 1024 |
| 11×14 | 1750 | 1375 |
| 16×20 (poster) | 2500 | 2000 |
This suggests a minimum resolution of 150dpi, though I believe the printers actually have a much higher “resolution” than that. Most print shops have ‘real’ photo printers, not dot matrix, so they don’t measure resolution the same way we computer people do, and they’ll interpolate up as they can, but this is probably a good minimum to start with. I’d double all those numbers, to be closer to 300dpi to start with. Remember that the “dpi” setting in photoshop really doens’t mean as much as the total number of pixels does.
That is a great chart and seems to confirm the 100 pixel per inch number I heard. I’m trying to see if I can get a 30″ x 40″ print from a photo that is 3118px x 2339px and it looks like it might not be as sharp as it would be 30″ x 22″.
Hi;
For some reason I’ve picked up 240ppi as the the sizing multiplier; so whether its for books prints or canvasses I normally export the file from lightroom at the size x 240ppi. For a 20″x 30″ canvas we’re talking 4800 x 7200 – this (in most cases) involves exporting the photo at bigger than it’s native resolution however :-S
Stephen, let us know how that works out. I’ve done prints of 16×20, but I don’t remember offhand how many pixels I packed into the image to get a decent print. Without looking at the chart I was thinking 240 or 270, 100 or even 150 seems low to me but the chart has worked – at least from the perspective of saying “don’t go larger than this” when I had to crop hard.
As for going larger than you’ve got, most of the photo machines seem to have decent interpolation; I haven’t seen anything concrete on what software is “best” if you have to grow your image.