I reviewed Pro HDR many years ago when it was among the first High Dynamic Range apps and best of the camera apps for the iPhone. In short order, Apple added HDR capability to its own software, but in general the third-party apps do a better job.
Pro HDR X (US$1.99) is a new app that has evolved from Pro HDR. It has solid roots, and this new app pushes your iPhone camera toward better HDR imaging.
Pro HDR X takes three images rather than the two that most HDR programs are limited to. In auto mode, the app analyzes the scene, picking the best exposure combinations to get you the best looking photo. If you want to do this manually, the screen presents three targets that you drag to the darkest area of your photo, to the mid-range tonal values, and to the brightest part of the scene.
The app can also edit photos from your on-board library, up to 24 Megapixels in size. When using the app, each exposure is precisely aligned, and the final images are saved at full resolution.