Your iPhone is remarkable in many ways, but its camera will simply never capture photos with a deliciously shallow depth of field like your DSLR. And unless Apple finds a way to cram a much, much larger sensor into the phone, that will always be the case. You can simulate that luxuriant, shallow depth of field effect through software, though. Tadaa SLR does just that.
Actually, Tadaa doesn't simply let you artificially tweak the depth of field; it lets you change the focus point of the photo. And it does that after you've taken the image, not unlike what you can do with the innovative Lytro camera.
You start Tadaa in camera mode; compose and take your shot. If you want to start with an existing photo, you can alternately choose one from your camera roll. There are a few widgets: Display a line of thirds grid, switch between a square or wide shot, and turn the flash on and off. Tadaa even gives you access to both the front and rear cameras.
After taking the shot, you paint a mask over whatever object you want to be in sharp focus. Tadaa has pretty smart edge detection, so you can just dab with your finger and the app selects the whole subject for you. If that's not working — and I did run into some subjects that Tadaa refused to select in their entirety — you can turn off edge detection and do the painting manually. In general, though, the trick is to slightly overpaint your subject so that Tadaa can find the edges.
After that, a slider lets you choose the aperture, which translates into the intensity of the depth of field effect. You can vary the effect from nothing, which gives you the deep depth of field the iPhone shoots automatically, to a very blurry background like you'd get from setting a DSLR to f/2.
And here's where Tadaa distinguishes itself from other blur apps like AfterFocus, for example. You can tap anywhere in the image to adjust the focus. Tap the background, for example, and it snaps into focus, simultaneously blurring the foreground objects that you've previously masked. This is a fun feature that lets you explore what a photo would look like if you shot the scene several times, varying the focus in each. Unlike the Lytro, though, you eventually need to make a choice and save the image — you can't continue to interactively change the focus after saving.
Another unique tool in Tadaa's bag of tricks: You can add and tweak bokeh. Bokeh can be a difficult concept to wrap your head around; it's the visual quality of the out-of-focus areas of a photo, and it often manifests itself as glowing blurs around reflective elements in the background. Using a pair of sliders — highlights and gloss — you can dial in an excellent simulation of bokeh, and get just the amount that you want. If you have every looked longingly at examples of bokeh in DSLR photography, you'll love fiddling with the bokeh in Tadaa; it delivers an effect that is essentially impossible to achieve with an iPhone in the usual way.
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