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Yet another feature once only found in expensive SLR cameras is making its way to smartphones: the buttery background blur caused by wide-aperture lenses. Google is bringing a simulated version of this blur to Android phones worldwide.

The feature is part of a redesigned camera app out today from Google, available only to devices running Android 4.4 (KitKat) and up.

Background blur, also called bokeh, is an optical effect made possible by the opening in the lens through which light passes — the aperture. The wider this is opened, the more light is let in (allowing for shots in lower light) but the narrower the area in front of the camera where the image is sharp — sometimes it can be just a fraction of an inch.

An example of background blur from a DSLR; the softness of the background highlights the subject of the photo.Devin Coldewey

Smartphone cameras don't generally show this effect because their compact lenses and sensors don't allow for the distortions of light necessary to create it. Simulating it is possible — but only if you can somehow tell how far away everything in the image is.

Google solves this problem by having the user move the camera after taking the picture, during which the software captures more images in succession, tracking objects and determining their distance. This creates a "depth map," and from there blur can be applied by the user to the background or foreground, and to whatever degree they choose.

In this picture, the focus can be switched between the background (left) and the foreground (right).Google

Others have achieved this with other means: Lytro's famous but impractical camera measured tiny differences in the paths of light waves, and the recently announced Nokia Refocus app uses a technique something like Google's but without the moving camera bit.

SLR users will doubtless mock this method as being as close to real bokeh as Instagram's filters are to the famous film stocks on which they are based. But fake or not, it's a tool any photographer, mobile or professional, will be glad to have in their possession.

You can read more about the technology at Google Research's blog post.