If you’re intending to self-publish – or supplying a picture to your publisher that might be used in a print edition, the three terms you’re most likely to hear are ‘bleed’, ‘CMYK and ‘resolution’.
They sound suitably mysterious but – as always – there’s no particular secret to them. And they apply both to potential cover photos and interior pictures.
Bleed – the printed content that spills over the intended final edge of the page, typically by about 3mm. This means pictures or background run cleanly to the edge of the finished page after it’s been trimmed. If you’re printing to a standard like A4, running ‘full bleed’ means using over-size sheets (‘supplementary raw format’/SRA, defined by ISO 217:1995 standard). That usually costs. But it’s worth it. The alternative is ending up with that “photocopier look” – the white edge where the ink doesn’t quite reach.
CMYK vs RGB – by default, images on a computer are RGB (red/green/blue) which displays by projected light on your monitor. Print, however, involves reflected light on paper and requires a different system – cyan, magenta, yellow and black. An RGB picture has to be converted to CMYK before it’ll print. Modern software often makes that switch for you, but be careful. Free utilities that can do it include GIMP and Irfanview. I use the latter all the time.
Resolution – Printing usually pivots on a resolution of 300 dots-per-inch (118.1 dots-per-cm), and you’ll often hear people ask for ‘print resolution’ or ‘300 dpi please’. Actually that’s misleading – it’s not enough to simply supply a picture at that resolution. The photos I publish on this blog are typically 650 pixels wide, which translates to 5.5 cm. Not enough (and yes, I do that deliberately). In fact, the “dots per inch” is irrelevant. What counts is the number of pixels over a given linear measure.
It works like this. If you’re trying to make a picture meet a standard Royal Trade book cover (C5 = 16.2 cm wide x 22.9 cm deep), you’ll need a minimum of 16.2 x 118.1 = 1,913.22 dots wide. To that you’ll have to add 100 dots for the bleed. Conveniently, a 10 megapixel camera shoots roughly this along the short edge of the frame, so a picture of this size (about 4.5 mB) will print OK. Inconveniently, a cover also needs allowance for the depth of spine and any wrap-around to the back, if the design’s intended to do that. Most books do, these days.
Have you ever wrestled with this stuff? Does this post help? I’d love to hear from you.
Copyright © Matthew Wright 2014
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