I was having an IM conversation with a friend of mine today talking about the resolution of digital cameras and what's needed for printing images out, in his case for large wall hung landscape prints.
Wednesday, August 12, 2009
My attempts to figure it out with him were basically along these lines.... The megapixels you need are not what you think they are. The current range of about 10-14mp is pretty damn good, and here's why.
First of all, heck out the print sizes for different digital camera resolutions. It has a nice explanation of sizes, printing needs, and most importantly, DPI. The accepted sizes that magazines print at is 300dpi, for close up viewing (about a foot or so I figure). For billboards, you only need about 40dpi according to the page.
I also found this megapixel calculator. It's pretty good, and given a pixel height and width it'll tell you things like filesizes and printed size given 300/150/72 dpi printing.
For example, put in the settings for the 6 megapixel Pentax *ist-D, with a maximum resolution of 3008x2008. You can see that you can get a high resolution (300dpi) print of 10x6" and a "photo" resolution print of 20x13" (which is pretty huge). If you're using screen resolution of 72dpi (still higher than the billboard setting) you can get up to 41x28". That's a 3 foot print from a "mere" 6 megapixels.
Bump it up to the 14 megapixel K20D and you can check out the 4672x3104 image size stats. This bumps you up to a 15x10" magazine resolution print (ie: larger than your standard magazine size), 30x20" photo print size and 64x43" for screen resolution.
Even if you take into account the photo resolution of 100dpi (which is probably more than is needed for viewing from a foot or more away in a home setting), you can get a 20 inch print out of a 6 megapixel camera, or 28 inches from 12 megapixel camera. And an image printed out at 20 inches by 13" is huge :)
Update: OK, so looking at this post from BoingBoing about the big $$ and big megapixel Phase One digital back, maybe I take back a bit about what I said regarding extreme cropping. The calculator shows that 60.0 megapixels (I chose the square cropping hxw) gives you a 25" square image at 300dpi. Kinda big :)
Posted by Alan Bailward at 10:29 AM