Camera Raw can now display a before/after Preview (with side-by-side and split-view support) to compare your edits to the original. The Preview check box in earlier versions of ACR has been replaced by three buttons in the bottom-right of the ACR main dialog. From left to right, they are Mode, Swap and Copy:
• Click the Mode button to cycle through left/right and top/bottom side-by-side and split-view modes.
• Click-and-hold the Mode button to bring up a popup menu for directly choosing Preview modes and accessing the Preview Preferences (the Preview Preferences support customizing the Preview modes used for cycling as well as some drawing options including divider and pane options).
• Tap Q to cycle through the Preview modes.
• Click the Swap button to swap Before/After settings.
• Tap P to swap Before/After settings for the primary selected image only.
• Shift + P to swap Before/After settings for all selected images.
• Click the Copy button to copy the After settings to the Before settings. This is useful for establishing a temporary “checkpoint” for your image editing session.
• Option + P (Mac) | Alt + P (Win) to copy After settings to the Before settings for the primary selected image only.
• Option + Shift + P (Mac) | Alt + Shift + P (Win) to copy After settings to the Before settings for all selected images.
• When making changes to images, the changes can only be made to the “after” image and the slider settings (in the panels) will always reflect the “after” image settings.
• The standard single-image view always shows the “after state”.
• Zooming and panning on one view will automatically zoom and pan the other.
Note: while tapping the Q key will cycle through all of the Preview modes in Camera Raw in Photoshop, I primarily use the same view 95+% of the time. So that I don’t have to cycle through so many different options, I click-hold the Mode button to display the pop-up menu for Preview Preferences. Unchecking all but one of the Preview modes allows me to tap the “Q” key to quickly toggle my Before/After Left Right view on and off.