Tapping the straighten angle knob kicks in the gyroscope, so you can tilt your device to get the exact angle you want. We don’t see a ton of these sorts of interactions that make assumptions about hardware capability and the user’s motor skills. Maybe that’s for the best?
Let’s take a look at the color adjustment features. You’ll notice the standard color adjustment tools you’d see in Photoshop or Pixelmator have been reduced down to four sliders. If we turn on the help labels, you’ll see what they adjust: