The Lens Corrections panel (Figure 4.72) now allows you to select various Upright (automated perspective) corrections. How this works is Lightroom first analyzes the image for straight-line edges and from this is able to estimate a perspective transform adjustment. Several Upright options are offered here, because no single type of adjustment will work perfectly for every image. These were arrived at after testing a large number of images, so it is always worth checking out each option to see which adjustment works best for an individual photo. They are as follows.
The Auto correction applies a balanced correction to the image, which rather than auto-selecting an Upright setting, applies a balanced combination of the options listed below. Essentially, it aims to level the image and, at the same time, fix converging vertical and horizontal lines in an image. The ultimate goal is to apply a suitable transform adjustment that avoids applying too strong a perspective correction. When selecting an Auto setting it mostly crops the image to hide the outside areas. However, if the auto adjustment ends up being quite strong, some outside areas may remain visible when applying an Auto setting. The Level correction applies a leveling adjustment only—this is like an auto-straighten tool. The Level + Vertical perspective correction applies a level and a converging vertical lines adjustment. And lastly, the Full correction applies a full level and a converging vertical and horizontal perspective adjustment, and does allow strong perspective corrections to occur.
Figure 4.72 The Lens Corrections Basic tab, with the Auto Upright option applied to an image. Each button has a mouse rollover tool tip that explains its function.
The Off setting can be used to turn off an Upright correction, while preserving the initial, precomputed analysis of the image. If you click the Reanalyze button, it switches off the adjustment and clears the memory so to speak, and when available, forces Upright to calculate a new transformation. It allows you to enable or disable a Lens Profile correction, which would otherwise affect how an Upright precalculation is made (note that Alt-clicking the Reanalyze button also resets). As you click on any of the above options (except Off), this automatically resets the Horizontal, Vertical, Rotate, Scale, and Aspect Transform sliders, as well as resetting any crop that’s active. It is important to realize that where an image has already been cropped or manually transformed, an Upright correction won’t work properly. Therefore, these settings need to be auto-removed when selecting an Upright setting. The only time a manual transform won’t be reset is if an Upright correction can’t be found. Also, when Upright is unable to do anything, informative text to that effect appears at the bottom of the panel.
Figure 4.73 The Lens Corrections Manual tab controls.
How Upright adjustments work
It is important to understand that the underlying math behind Upright adjustments is doing more than just auto-setting the Vertical, Horizontal, and Rotate sliders found in the Manual tab section (Figure 4.73). The vertical and horizontal adjustments involved in the Upright process are actually quite sophisticated. Behind the scenes there are angle of view and center of projection adjustments taking place. It’s all to do with the fact that the interaction of one rotation movement can have an impact on another, and such interactions can be quite complex. Think about what happens when you adjust the tilt and yaw on a camera tripod head, and you may get some idea of the problem.
The Upright adjustments aim to correct the perspective in such a way that having the choice of four different methods should mean at least one of these will work best. What tends to happen, though, is the perspective can often end up looking too perfect. When correcting the perspective for a building, where you are correcting for a keystone effect, it is generally a good idea to go to the Manual tab afterward and adjust the Vertical slide, adding something like a +10 adjustment so the corrected verticals converge slightly. You might even consider creating a preset that combines an auto-perspective correction with a Vertical slider tweak.
It is inevitable that extreme adjustments may cause the image to distort so much that you’ll end up seeing white padded areas (like in the following example). Where this happens you can check the “Constrain to crop” box to apply an auto crop adjustment that trims the image accordingly. Or, you can always apply a manual crop to the image afterward to determine the crop boundary. In the Manual tab section the Scale slider can be used to reduce or enlarge the image after making an Upright adjustment. There is now also an Aspect Ratio slider, which is useful for tweaking the results from an Upright adjustment. With perspective corrections, although you may end up being corrected for perspective, the resulting image may look vertically or horizontally stretched. Using the Aspect Ration slider you can adjust the amount the image is stretched vertically and horizontally so the perspective looks more natural.