How much fine detail do you need in a photograph for it to look sharp? How much fine detail can your printer deliver? Both of these questions have been the subject of gigabytes of verbiage, most of it hearsay, untested and unfounded. It seems like everyone has an opinion; pathetically few of them are informed opinions.
A few weeks ago I stumbled upon an easy and robust test that you can run to find the answer for yourself. In this column I'll tell you how to determine how much detail your printer can make use of and how much of that fine detail you actually care about.
Understand, here, that I'm not talking about what constitutes "perfect" sharpness: the point at which adding more fine detail to a photograph makes no difference whatsoever in your perception of its sharpness. I've run those experiments, and the number is phenomenally high. You need hundreds of megapixels. Forget it. You're not making photographs (or scans) that good, and even if you were, your printer can't render detail that small. (Traditional printers should not be feeling smug; you can't do it in the darkroom, either, unless you're making contact prints from very high quality negatives.)
The question we're concerned with is what you can achieve in practice and what looks "good enough." Now, understand that "good enough" is going to depend upon subject matter, viewing distance, choice of printer and paper, and printer settings. Everyone's going to get a different answer. The nice thing about this test is that it takes all of that into account. It comes up with answers that will work for you.
Along with a printer, you'll need the following items to perform this test:
• Three to five sheets of paper.
• A copy of Photoshop or Photoshop Elements or any other program that can generate a "contact sheet" from an assortment of files.
• A folder on your computer with several dozen different image files in it, spanning the range of things that you're likely to be printing.
(Note: Do not use synthetic test target files like bar charts or checkerboards or other such things. They can produce weird and anomalous results that are not at all germane to how your photographs will print out.)
• A good magnifying loupe, good enough to be able to clearly see the dots in your inkjet prints.
Now you're ready to roll.
I'm still using the "Contact Sheet II" operation from older versions of Photoshop (figure 1). It's what I know and like, so that's the process I'm describing here. Bring up the contact sheet control panel, point it at your file folder, set the rows and columns to something like 7x7" or 8x8", set the page size to 8x10", and set the resolution to 300 ppi. Let'er rip!
After the contact sheet has been generated, print it out on an 8.5 x 11 sheet of paper, using whatever printer settings you wish to evaluate. In the illustrations in this article, I was using an Epson Stylus Photo R800 printer, printing on Epson Premium Semigloss paper at the highest quality setting.
Repeat this two more times with everything the same except for changing the contact sheet resolution to 600 ppi and 1200 ppi in the Contact Sheet II control panel (figure 2). You'll now have three superficially-identical prints. You may want to mark them on the back so you can tell them apart.
(If you want to refine this further, generate two intermediate-resolution prints, at 450 ppi and 900 ppi, but don't try to split it finer than that. You really won't care, and it's hard to see smaller differences even if they're real.)
Look at the fine detail in the prints with your loupe. If it's a recent-model printer being used at a high quality setting, you will likely see a difference in the amount of fine detail being rendered between the 300 ppi and the 600 ppi prints. You may or may not see a difference between the 600 and 1200 ppi prints. I did, in my tests (figure 3).
Look for the point at which the fine detail stops improving. In other words, if the 450 ppi print shows more fine detail than the 300 ppi print, but the 600 ppi print doesn't show more fine detail than the 450 ppi print, it means that your printer can't make use of more than 450 ppi of data.
Now you know what your printer's limits are. Of course, this will vary with the paper you use and the printer settings to use, so don't try to generalize. Generally, glossy papers support higher resolutions than matte papers, but you never know until you run a test.
So much for the pixel-peeping. Now you're going to find out how much of that fine detail actually matters to you. Just look at the prints. You get to decide what distance you're viewing them from, what the lighting conditions are, and how persnickety you want to be. Can you tell sharper prints from fuzzier ones? Which of those little contact sheet images look different? Higher resolution matters more for some kinds of subject matter and photographs than for others.
How many ppi do you need before it stops mattering to you? Remember there's no right answer to this exercise. I suspect you will be surprised if the answers you get. Some people will find that they're happier with much lower resolutions than they thought they would be. Other people find that they can see a lot more fine detail than they thought.
In case you're wondering, my "sweet spot" for most of my printers and the kind of prints I make, is in the 450-500 ppi range. As a rule, prints look visibly fuzzier to me if I drop to 300 ppi, but they don't look obviously sharper if I go to 600–900 ppi. But that's me. I guarantee your mileage will differ.
Of course, once everyone runs these tests, all the interminable online arguments about print and printer resolution will cease.