As this first blog post of 2014 is being published rather later than intended, instead of talking about New Year’s Resolutions, let’s take a look at image resolution.

It used to be that writers only needed to concern themselves with words, but now that practically everyone owns a scanner or a phone with a camera, and enhanced ebook formats for tablets allow us to include our own photographs and illustrations in our books, we all need to know something about the way in which digital images are displayed.

Simply put, a digital image is made up of lots of coloured dots or pixels, which are spread out regularly like the squares on a piece of graph paper or the stitches of a cross-stitch embroidery. A pixel – a picture element – is the smallest point that can be identified and addressed on a screen: it can’t be split into parts and can therefore only be a single colour.

Historically, standard computer monitors had a resolution of around 72 ppi – that’s 72 pixels per inch, so to fill a square inch of your screen, you’d need an image with 72×72 pixels, and to fill a four inch square you’d need 288 x 288 pixels.

Obviously the more pixels in an image, the bigger the file size. So if you want to send a photo via email or use an image on a webpage, it’s best to keep it small so that it doesn’t take too long to load. But if you make it too small, the computer won’t have enough information and will either show a tiny image or the missing data will have to be invented.

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