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 16x20” @ 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 16x20”, in Pho­to­shop works out to be 6x9” @ 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 [email protected] 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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