DPI ain't nothing but a number

In the glamorous world of Web Design, 95% of time with clients is spent discussing the same two or three basic points about image size, so I’ve attempted to write up a short set of answers to which I could point them. I have tried to be brief and funny, but also useful. I’ve also tried to keep my tone free from the exasperation I often feel when going over these points for the third time in a day. Graphic designers out there, tell me what points I’ve missed and where I could be clearer. If you want to use this as a reference in your own correspondence please do.

How big should my image be?

Short answer: 1000 pixels on its longer side. PNG or possibly JPG and less than 1 MB file size. Long answer: see below.

Why is this image “too small?” It’s 300 dpi!

In print, the magic standard is 300 dpi, meaning that an image has three hundred pixels per inch at the size it will be reproduced. If your image is 300 dpi but only one inch wide, and you want to fill a double-page spread with the image, it will have to be blown up to seventeen inches and all those tiny pixels will be seventeen times as large so now your image is effectively seventeen and a half dpi.

On the web, dpi is meaningless, because you might be looking at an image on your grandma’s ’95 Gateway or on next year’s Apple Watch: you have no idea what size those pixels are. It’s more important to think about how many pixels wide and high an image is so that the designer can think of the amount of space in a window it will occupy.

A nominally high-resolution image becomes low-resolution when presented at a different size

Zoom to enhance?

You can’t reveal detail that isn’t there. An image that is out of focus or noisy will be more out of focus or noisy when blown up. If the image has sharp lines, like the edges of letters, those will degrade. If you have an image of an old newspaper, you will need to capture all the detail you want at the photography/digitization stage. Words are a special case. People notice blurry letters much more than they notice blurry photos. So if you are digitizing anything you want your viewers to read, crank up the resolution on your scanner.

I compressed it! Aren’t you proud of me?

There are lots of ways image encoding systems save disk space. Some take advantage of redundancy in the data and don’t affect the way an image looks. Some take advantage of the way the human eye works and these can mess with the quality of an image. The biggest offender here is JPEG compression. This system uses a complex mix of math and psychology to trick the eye into seeing more detail than the file contains. But if you compress things too much the image will degrade, becoming jagged or spotty. This is particularly true of images with sharp lines (like text) or flat colors (like cartoons). For these images, PNG is a better format.

While JPEG compression can save disk space, its flaws are particularly evident with hard-edges and flat colors.

What about bit depth?

Bit depth is a measure of how many different hues an image can have. In theory, the more bits, the more discreet colors are available. In practice, people really can’t perceive the subtleties after a while. There are those who claim there’s a huge difference between 8 bits and 16 bits per channel. Those people are lying and they have too many figurines on their desks.

Is there anything else I should know?

There’s a ton of other stuff to know about digital images, from alpha channels to color spaces. Do you need to know these things? Are you a graphic designer? Then the answer is no. Ultimately the most important stuff is not technical. Is it a good photo? Is it in focus? Does it have white whites and black blacks? Is it not too grainy? Is it grainy enough? Do you like it?

Paranormal, Don't You Know

Downton

MATTHEW
BOO, I say, what.

MARY
How now? Whatever is this ghestly apparition, don’t yew know, at my window, all a-peekin’-in?

MAT
AHA Mary, darling, ’tis I, your own Matthew, breechin’ the space between worlds. I hev become a Heathcliff, wandrin’ the moors and tappin’ at panes.

MAR
Oh Mathyew, yew nevah did read much, did yew? But it’s not your brains that my loins miss so. Come in and revish me, my sweet zombie cousin!

MAT
ALAS Mary deah I am unable to engage in such congress. I am only heah to do this one cameo for the Christmas special and then I must dress properly before poppin’ back to the afterlife for drinks.

MAR
But Cuz, tell me—what is it like, yew know, in heaven? Dost one hev all the staff one can no longer afford here on Earth in these trying days of post-industrialization?

MAT
It’s a bit of all right—evah so many people there—that footman fellah who died in the war, for one, what’s his name—and oh, Sybil is there—and—take this kindly—only she’s very dull—pretty to look at but—well, you may hev dodged a bullet with her dyin’ and all—OH and the funniest thing, your cousin is there, the one thet died on the Titanic, only he says he suspects sabotage, somethin’ about bein’ cheated out of an inheritance—

MAR
Oh Mathyew, let’s not talk of characters no one remembers anyway. How long hev yew left with me, my toe-headed spectre?

MAT
Not long, my pet—I may gaze on your eyebrows but a moment longer—and Mary, there is one thing—

MAR
OH tell me! Tell me anything.

MAT
Mary… Edith’s quite the bitch, what?

MAR
OH MATHYEW I’VE MISSED HEARING THAT MOST OF ALL.

April is the cruelest month

ditch

My Grandfather Cox scared me. He wasn’t an angry man, and he never threatened corporal punishment the way my other grandfather sometimes did. But he was a large and serious man. He was a Methodist minister and thought having a pack of cards in the house was an invitation to a life of debauchery. He spoke low, calmly, and infrequently about important things like religion and how not to waste your money on comic books. He and Grandmother Cox lived in a spare one-story house in rural Indiana with a long treeless lawn stretching to the country road. There was a drainage ditch along this road and at the end of the driveway a culvert made from four-foot aluminum pipe, ubiquitous in the Midwest.

My older brother, Rob, and I were staying with my Grandparents for a week in early spring. One morning we were sitting on the concrete front step with nothing to do—the absence of cards was only part of a more general ban on fun; the only diversions in the house being a bible trivia game and a dish of Kraft caramels. Grandfather Cox had been down by the edge of the road inspecting the ditch for some time and he abruptly strode with purpose towards the two of us. I had a sense of unease. Grandfather caught my gaze and brought his finger to his lips. Rob and I waited until he made his way to us and bent down. “Boys,” he whispered, “there’s a groundhog in the drainpipe. If you each go to a different end and are absolutely quiet you will see him there.”

I was confused. Rob and I both loved nature and watching animals (and sometimes catching them and bringing them home in pillowcases to the alarm of our mother), but groundhogs weren’t so special. In addition to being distrustful of fun, Grandfather Cox had never expressed any opinion about animals or the wonders of nature. But his eyes were twinkling and he seemed to be having a moment with us, and those were rare. So Rob and I walked very slowly to the edge of the road, covering the twenty or so yards in about two minutes.

We split to opposite sides of the gravel driveway and slid on our cutoffs down the brown dead sloping grass. I cautiously inched my head around the side of the pipe, ready at any moment for the beast to scamper out in terror, but as my angle of vision made its way down the pipe, there was nothing but dirty sediment. Finally I saw light at the other side, and Rob crouching in silhouette.

We stayed like that, staring for what felt like a very long time. Eventually, we stood up and walked back to the house, faster than before but still in silence. Grandfather was standing by the step as he had been the entire time, smiling with a look of benevolence bordering on grace.

“Grandpa,” I said, “there’s nothing there.”

“April Fool’s,” he said, without any particular inflection. And then he went inside.