As noted a couple of days ago, I’ve been reading the excellent Photoshop Elements for Digital Photographers by Scott Kelby. This provokes two meditations today; this on the observation that computer geeks and photo nerds come from different planets, and another on integrity, which is seriously in doubt.

I, like many geeks, am entirely self-taught in computer image processing. The tools are tricky, but it’s conceptually simple: you’ve got a rectangular array of coloured pixels that you got from a camera or scanner or friend, and you fiddle with it, then you publish it on the Web.

Per Inch? · All this software comes with controls and readouts of the “dots-per-inch,” but I always ignored that because I’m a Web Guy and Web Guys do pixels.

In Belkin’s book, he talks quite a bit about resolutions, and I can read the English sentences and find all the nouns and verbs and everything, but it’s clear he’s coming from another planet. Consider this discussion of preparing an image for print:

It’s pretty clear that we’ll need to increase the resolution to get good results. I wish we could just type in the resolution we’d like it to be in the Resolution field field (such as 200 or 300 ppi), but unfortunately, the “resampling” makes our low-resolution photo appear soft (blurry) and pixelated. That’s why we need to turn the Resample Image checkbox off (it’s on by default). That way, when we type in a resolution setting that we need, Elements automatically adjusts the Width and Height of the image down in the exact same proportion. As your Width and Height come down (with Resample Image turned off) your resolution goes up. Best of all, there’s absolutely no loss of quality. Pretty cool!

Pretty cool? Well, when you’ve turned off Resample Image and you change the resolution, it uses the miraculous techniques of arithmetic, invented by the Sumerians approximately six thousand years ago, to divide the number of pixels by the number of pixels per inch and (astounding!) compute the number of inches. There are apparently intelligent, competent people who find this note-worthy. Furthermore, they include some of the authors of Photoshop; since Resample Image is on by default, some programmer somewhere thinks it’s sensible, when you change the resolution, to hold the size constant and recompute the image. But... there really is no resolution dammit, it’s just a bunch of pixels! I am reminded of the famous Australian sheep-counters who can tell the size of size of a herd of sheep at a glance; they trick is, they count the legs and divide by four.

Since Mr. Kelby is a fine author and clearly a master of this technology, I can’t just dismiss this world-view as stupid or intrinsically wrong. It’s simplest just to say they’re from Planet Photoshop, and I’m not.

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March 15, 2004
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