The Library module in Adobe Photoshop Lightroom 3 is designed to make it easy to import, evaluate, and organize your digital photos. This article covers three of my favorite Library features, including the ability to compare similar images side by side, in detail. We'll also take a look at the different types of attributes that you can apply to images during this process, and how you can use those attributes with the Library filter to display only the shots that you need from one session to the next.
For additional information about these features, see tips 13, 14, and 16 in Adobe Digital Imaging How-Tos: 100 Essential Techniques for Photoshop CS5, Lightroom 3, and Camera Raw 6.
To start, you'll need two images in the folder you're viewing. Choose images that have similar composition and exposure characteristics[md]enough so that just looking at large thumbnails won't give you a complete sense of how the two images compare in terms of quality and detail. This is a common situation for most photographers; we learn early and often that photographing important subjects requires the use of subtly different perspectives, camera settings, and lens settings, to get the shot we want.
Using the Library module, select two similar photos from the Grid view and press the C key to display them within the Compare view. You'll immediately see both images, enlarged and sitting side by side in the main window (see Figure 1).
Figure 1 After you highlight the two images you want to compare, pressing the C key invokes the Compare view in Lightroom 3.
In the Compare view, the Select image is on the left, and the Candidate image is on the right. The active image will have a thin white highlight around its edges. To swap out one of your originally selected shots, click either the Select or Candidate preview, and then click a different picture in the Filmstrip. The Select image is identified in the Filmstrip by a white diamond icon in the upper-right corner of the thumbnail, and the Candidate is identified by a black diamond (see Figure 2).
Figure 2 You can swap positions of the Select image and the Candidate image, or replace either or both with other images in the Filmstrip.
When you're ready to compare the photos, you'll probably need to examine them at 50100% magnification to verify that the most important details are in focus. The Zoom slider (located just below the Select preview) lets you magnify the images in tandem.
When necessary, you can also magnify and work with the images independently. To do this, first click the gold lock icon below the Select photo; this action turns off the zoom and pan synchronization between the two pictures. Once the images are unlocked, you can select either photo and then use the Zoom slider to change the image's magnification. This feature is helpful when you've photographed the same subject with the same focal length but at different distances, or differing focal lengths at the same distance. In either case, parts of your subject will have a slightly different scale in one shot versus the other, so comparing them in this way can help you to determine focus and noise levels more accurately.
It is likely that you will also need to pan around the two images, to compare different parts of the shots while looking for focus defects or other potential issues. To do this, click either of the images and drag. As noted before, you can pan across an image independently by making sure that the gold lock icon is "open." Using our example of two shots with different focal lengths, once you've created a similar scale between objects in the two photos by zooming independently, you can then pan both images independently to position the subject in each shot in the same part of the frame. From there, you can click the gold lock "closed" so that you can pan across the images together and continue comparing the details in each shot (see Figure 3).
Figure 3 Compare mode allows you to zoom in on (and pan around) each image independently, in order to give your subject relatively similar position and scale inside the window.