Why sharpen your images?

This week, I received a rather good question from one of my old friends, Cindy. She was wondering “how come that whenever I’m taking digital images, I have to sharpen them afterwards?” Good question, and of course, it’s already one step ahead of the curve, in that the question presupposes that yes, you DO have to sharpen your images. Which is correct… But why?

Back in the days of film, things were simple: If you wanted your photos, you got prints made. These prints were predictable: They’ll be on paper, have a certain dynamic range, etc. Then digital photography came along and turned everything on its head, because suddenly there are so many more things you can do with your photos…

You can project them on a wall (in a series of different resolutions, depending on the projector), you can upload them to a website, you can have prints made, or you can print them in magazines in newspapers. This is where part of the problem comes from…

Mathematically, (which is, of course, how computers think), it is far easier to sharpen an image than to un-sharpen it – It’s important to remember, for example, that un-sharpening an image is not the same as merely blurring it: The quality of the resulting fuzziness is completely different.

Camera manufacturers know this, and this is where one of the biggest differences between the way images are processed inside an SLR and a digital compact are different:

Digital SLR versus compact cameras

The manufacturers assume (correctly, most of the time), that people shooting with compact cameras don’t plan to do much to their photos after they are downloaded onto their computer. So, how do you make the photos look as good as possible? By sharpening them in-camera, so they look gorgeous right away. You take one look at ‘em, are happy, and upload them to Flickr right away.

All good and well, but people photographing with an SLR camera are different. For one thing, they’ve paid a lot of extra money for the flexibility and choice that is inherent in a SLR: You can choose lenses, shutter times, ISO values, and all that wonderfulness. It is therefore safe to assume that an SLR user wants more control over the final image, and for this reason, photos coming out of a digital SLR are generally sharpened less – in some cases, you will even see that photos coming out of a digital compact appear sharper (and therefore better) than that from an SLR.

Quirks of sharpening

As already has been mentioned, it’s easier to sharpen than to de-sharpen an image. There is a second quirk too, however: It’s never a good idea to re-sharpen an image (i.e. sharpen a photo that has already been sharpened). This is the crux of why you can ultimately get better photos out of a SLR: you evaluate the photograph, and experiment with the amount of sharpening you do. Then, once the preview looks good, you run the sharpening on the photograph, and then never sharpen it again.

Photos from most digital compacts have, of course, already been sharpened once (inside the camera), so if you try and re-sharpen them to get more clarity out of them, you’ll never get the same level of woah-factor, because you’ll start getting sharpening artifacts (thin white lines around the areas that have been sharpened): What, in fact, happens is that the software isn’t sharpening the image itself, it’ll start sharpening the parts of the image which has already been sharpened. Sometimes this can lead to interesting effects, but often you just lose any subtlety to an image.

It’s also worth noting that sharpening often amplifies the downside of JPG image compression: If your photograph has been compressed too much (such as when you shoot on ‘medium’ quality on your camera, rather than ‘superfine’, or whatever the highest quality setting is), you might find that suddenly you’ll get a lot of ugly banding and compression artifacts showing up that were practically invisible before.

So, in-camera sharpening is bad?

Hmm. Not necessarily: I never really do all that much editing on casual holiday snaps, for example, so I leave my Canon IXUS compact camera set to ‘high sharpening’. It means I can upload my photos straight to Facebook, and they’ll look pretty decent.

When it comes to artistic control, however: Yes, in-camera sharpening is bad. There are two ways around this: Turn the sharpening down as much as you can in your camera (your photos will look a lot worse when you look at them the first time, but when you sharpen them on your computer, they’ll really zing), or shoot in RAW format (which, if you want full creative control, you should be doing anyway, but that’s for a different article).

So, how do I sharpen my images?

Hah, that’s a completely different article altogether. Luckily, I’ve already written that one – head over to Sharpen those photos: Unsharp Mask for more info than you ever wanted about this topic!