An App to Lend an Artsy Blur to Photos Roy Furchgott for The New York Times Tadaa 3-D lets users mimic dimension in images typically reserved for Digital Single-Lens Reflex cameras by highlighting parts they want to focus and applying blur and effects to the frame. The Tadaa 3D app for Apple products adds an arresting effect to your photos, making a foreground object move around when you tilt your phone, like an old postcard with a plastic lenticular 3-D screen. But the app, which costs $3.99, can be tricked into providing an even more useful photo effect - "bokeh," a blurring of the background to draw the eye to the main subject - that is usually reserved for digital single-lens reflex cameras with a high-end lens. Bokeh is used in many artful photos, especially in portraits. Generally you can't get bokeh with a mobile phone or tablet camera because of limitations of the lens. Here is where the Tadaa 3D app comes in. You start out as if you were making a Tadaa 3D photo, by using your finger to draw over the part of your photo you want in focus. You can be pretty sloppy about it if you leave "Detect Edge" on; the app will help you isolate your foreground. The parts to remain focused will turn green. When you hit the apply button, everything not green will go blurry. You can then add filter effects, like making your picture black and white as you would with Instagram or other photo apps. Now you have a photo that has a blurry background and that appears to change perspective as you move your phone or tablet around. To see the 3-D effect you have to view your photo using the app, or on the Tadaa Web site. You can share the shot to Facebook, Twitter and Tumblr as well as to the Tadaa shared site and send a link to your picture on the site by e-mail. I like the bokeh effect without the gimmicky 3-D part, but Tadaa offers no way to save a static version to your phone. You can cheat by taking a screen shot. Just tap on your finished Tadaa shot to make it full screen, then press the round "home" button on the face of your phone or tablet at the same time as the power button on the top. That takes a photo of what's on the screen and puts it on your Camera Roll. You may have to use the crop tool to trim off some border, but you end up with an eye-catching image with bokeh, no costly D.S.L.R. needed.