This isn’t your normal filter app. The hint’s right there in the icon. Instead, Darkr tries to recreate the process of using a real-life darkroom to develop your photos. For starters, your camera roll appears as a bin of negatives. Select one, and it gives you a digital test strip to find the correct look, then takes you into an editor where you can crop, rotate, dodge, burn, blur, and tone the image. It has several built-in camera modes, including one that mimics a large-format camera, and as you might expect with a past-obsessed app, it only produces results in black and white.