This week's tip deals with the Manual Correction controls that are part of the Lens Corrections pane in Lightroom 4. Using these controls, we can correct the geometric distortions that are present in this wide-angle and low-angle shot of a church interior.
Click on the image to get a larger view. If you look closely, you'll notice a number of issues we need to correct. First off, we have some barrel distortion. The image appears to be bulging towards us. At the same time, we also have a strong perspective to deal with from being at a low angle to the altar. This causes all of the vertical lines to converge as they go up giving the appearance that the wall is receding away from us. If you've ever tried shooting a tall bulding from a low angle you know how hard it can be to get an image without this distorted perspective.
Lightroom offers us Lens Correction tools to compensate for all of these geometric and spatial distortions we are seeing. Before you even get into the Manual Correction, you should start by enabling Lens Profile Correction for the image you are working on. This will take care of the geometric and chromatic distortions inherent in your lens by applying an Adobe-generated Lens Correction Profile that was created to remove vignetting, barrel distortion and chromatic aberration for your particular lens. Make sure that the correct lens is chosen by Lightroom from the image metadata. Occasionally, Lightroom will fail to properly detect the lens and you will have to manually chose it from the drop-down menus. Once you have the Profile Correction in place, you are ready to make more radical geometric changes to your image using the Manual control.
Start by going to the Lens Corrections panel in Lightroom and then toggling over to the Manual section where all of the control sliders are located. These sliders allow us to transform the image plane in three dimensions. Distortion controls how convex or concave your image is. (How much it bulges toward or away from you.) The Vertical and Horizonal sliders control the X and Y axis for your image allowing you to tip it forward, backward, left, or right in the viewing plane. The Scale and Rotate sliders allow you to move the image plane closer or further away as well as rotating the image within that plane.
Now that we have some idea of how the manual sliders work, let's work through the image. First we will correct the bulge by moving the Distortion slider up to +14. Next, we'll fix the vertical perspective problem and "tip the image forward" by moving the Vertical slider to the left. Somewhere around -41should get us close. A slight Horizontal adjustment of +3 brings everything up to square. Finally, we'll scale back to 77 so we can see the entire corrected image.
Here's what the corrected image looks like. (Click the image to see a larger view.) It's not perfect but it's a lot more appealing to the viewer. Notice how much of the geometry we've been able to fix with the manual control. Verticals are now square and upright, no longer tilted away from the viewer. The trapezoidal windows have been squared up again, the columns are straight, the altar artwork is in a flat plane again and the bulge has been taken out of the room. By making these changes, we are brining more of the image into the same plane as the viewer.
As a finishing step, you may wish to crop down some of the grey areas revealed by the Manual Correction. The Content-Aware Fill tool in Photoshop can be handy for filling in areas you don't want to crop out of the final image.
Here's another tip: This corrective technique is great for solving the problem of having to shoot framed artwork behind glass without catching reflections and glare. The solution is to shoot the glass "off-angle" to the left or right to minimize reflections and glare and then to make a horizonal manual correction in Lightroom to pull the image square and back in-plane again. This has saved my bacon more than a few times when shooting in less than ideal situations.
