I have a friend that attended one of my classes and was working on making enlargements of his digital photos for an art show. He asked how to ensure the prints had good quality up large… what numbers in Photoshop would ensure a good large print??

Here’s what KodakGallery Recommends:

Print size Minimum recommended megapixels for print size Minimum recommended resolution (pixels)
Wallet
(2 x 3″)
0.1 360 x 240
4 x 6″ 0.6 930 x 620
5 x 7″ 0.7 1008 x 720
8 x 10″ 1.3 1280 x 1024
16 x 20″ 1.8 1600 x 1200
20 x 30″ 2.2 1600 x 1200

In Photoshop, I would suggest 225 PPI/DPI is very safe at the size in inches you’ll be printing… so is Photoshop shows you can be at 16×20″ @ 225 PPI, then you are good.
From practice I know you can go much lower, but I try to not drop below 200 PPI @ the final print size just to be safe. The Kodak info above is quite a bit lower than that, and they are a lap that will make the prints with that minimum. What they say for 16×20″, in Photoshop works out to be 6×9″ @ 200 PPI… once again, these are their ‘minimums’.
If I want to go really big on a photo, I use Genuine Fractals.

But that’s $150 investment.

And you can upsample the image in Photoshop, but using GF is a somewhat higher quality. If you start with a very nice file, with very little artifacts (like film grain), you can go huge in GF. That’s with a low-compression JPeg or RAW file. If you took a tiny JPeg, that was highly compressed in the camera, and maybe wasn’t the sharpest file to begin with, any upsampling to give it more pixel resolution won’t really help.

‘Resampling’ is a checkbox in the Photoshop menus, Image Menu/Image Size. I tell everyone when they are changing a photo for most uses going bigger to have the ‘Resampling’ box unchecked, so that the image quality won’t suffer. You would leave it checked to have Photoshop add some fake pixels to try to make the image have a bit more resolution to print better at a large size. Genuine Fractals is a Photoshop add on that is designed to do the same thing, just a bit better.

PhotoshopScreenSnapz001

As a side note, if you are making an image smaller, you leave the ‘Resampling’ box checked, as you are throwing away pixels and if you don’t have it checked, you are not really making the file size smaller (like for the web, or an e-mail photo).

Your best bet is to just do a test print early at the size you want to use and see how it looks. Maybe one with the normal file, and one with a resampled file to get to 200PPI@ the print size… and see how they compare. Let me know how a test like that goes.

The last point is what sort of camera you use. A file from a digital SLR of any price is much more likely to handle upsampling better than a file from a little snap camera. I discuss that in my class, but the image sensor is soooo much bigger and better in the SLRs (the bigger cameras where you can change lenses), and they invest a lot in how they compress the Jpeg files.

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