Of course, to have this conversation between desktop, cloud, and mobile repositories, you need an active Internet connection. If you know you'll be without access but you still want to work on certain images, you can enable a collection for offline editing, which copies Smart Previews of all its images to Lightroom mobile. Once you're back online, any updates you've made will sync back to Lightroom desktop.
All aboard the mobile editing train
Lightroom mobile wouldn't be nearly as interesting if all it did was sync photos for viewing on the iPad, which is why the app includes most basic tools you'd need for editing photos on the go. It contains all the image adjustments found in the Basic pane of Lightroom desktop's Develop module, such as white balance, exposure, contrast, clarity, and vibrance. It also includes several presets for applying black-and-white and color filters, specific looks, and tones; and a crop tool that can straighten, rotate, or lock the photo's visible area to specific aspect ratios. (Hint: When you tap an aspect ratio, such as 5 x 4, tap the button again to toggle the crop area between landscape and portrait orientation.) The app doesn't recognize user-created presets, but I can imagine that option being incorporated in the future.
In place of some granular settings, Lightroom mobile offers effects presets; for example, "Vignette 2" gives your picture a noticeable dark halo, but you can't control the halo amount or the feathering of that effect until you work on the image in Lightroom desktop. Similarly, there are only two sharpening controls — found in photo presets containing faces and photos that are "scenic."
Rather than try to replicate Lightroom desktop's interface by cramming controls into an onscreen box, the app's tools appear in a sliding row at the bottom of the screen. Lightroom mobile takes advantage of the touch interface for many of these controls: For example, you can tap the screen with two fingers to hide or reveal additional information such as a histogram and metadata (the capture settings, lens, and camera model) in the editing interface, or badges and metadata in the Grid view.
Adjustments you make in Lightroom mobile remain editable in Lightroom desktop, and vice-versa. For example, increasing Vibrance to +14 on the iPad sets that control at the same point for that image on the desktop. The mobile app doesn't include a detailed History pane, but you can reset an image back to its imported original state or to basic tones; additionally, touching the screen with three fingers switches to a Before mode so you can compare your edits with the original version.
The app also incorporates a minimal-but-effective version of Lightroom's adjustment sync between photos (such as when you want to apply the same settings to multiple similar shots). Start at your reference image, then move to the photo you want to edit and tap the Previous button at the bottom of the screen to apply either all adjustments or basic tones from that first image.
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