Many (including myself) say that Capture One Pro is more advanced than Lightroom. It just has more useful features and a more professional workflow. One of those feature is the Keystone tool.
The keystone effect, also known as the tombstone effect, is caused by attempting to project an image onto a surface at an angle, as with a projector not quite centered onto the screen it is projecting on. It is a distortion of the image dimensions, such as making a square look like a trapezoid, the shape of an architectural keystone, hence the name of the feature. In the typical case of a projector sitting on a table, and looking upwards to the screen, the image is larger at the top than on the bottom. Some areas of the screen may not be focused correctly as the projector lens is focused at the average distance only.
What is means to product photographers is that if you’re shooting something looking down at it (at, let’s say, 30°), the vertical lines of the object will not be vertical anymore. That’s a problem I have encountered many times.
So, to fix the situation, Phase One ships Capture One Pro with the Keystone tool. It’s super easy to use. Just place the four (or two, depending on what version of the tool you’re using) lines where the major edges of your product are. Then, hit Apply and the program will correct your image.
If you’d like a little more granularity with the corrections, head over to the tool’s panel at the left of the interface. The Vertical and Horizontal sliders dictate how much of the effect is applied, individually. The Amount slider does the same but combines the Vertical, Horizontal, and Aspect parameters. Speaking of, by moving the Aspect slider, you will stretch your image to be longer and less large or the inverse, depending on the setting you inputted. Finally, the Rotation option turns your photo left or right. The unit is in degrees.
To get the best result, follow these tips.
Align the lines with the longest, biggest and more prevalent edges of your photographs. These are the ones you see the most, so it only makes sense to base your Keystoning with these. Also, the smaller edges are usually attached to these so they will follow.
If the line is not straight (bowed), use the points farthest from the center of it. Every lens has some pincushion distortion that renders the lines bowed. That can be fixed in the software. To make this tip valid, however, the center of that edge (if it’s a horizontal line) must be at the X center of the image sensor so that the bow is equal everywhere. Also, the point from which you place the Keystone dotted line need to be equidistant from the middle of that edge (that is at the middle of the image).
As good as the tool is, it’s not perfect. If you have the choice, shoot the image so the less keystoning happens. If you know that you’ll need to correct the photo later, shoot wider than what you want for your composition because some cropping will occur. The more extreme the corrections, the more cropping you’ll get. The best way to correct the tombstone effect in-camera is to use a tilt-shift lens. With these, you can manually tilt or shift the focus/image plane and correct for the keystone. The downside to such lenses is that they are more expensive, less popular and bigger/heavier than traditional optic.
Verify that the tool has done it’s job properly by using guides. You can access them by going to View > Add Guide > [Horizontal or Vertical] Guide. Just put your cursor over the guide and slide it to the same edge that you used to correct the keystoning. They should match at every point of the line. Fun fact: Before the release of Capture One Pro 8.1 (less than a month ago), you only had one vertical and horizontal guide and you did not have any info as to where it is on your photo. See what some of the new characteristics of 8.1 are here.
Use the Vertical/Horizontal Keystone tool to correct on one axis only. Sometimes, you just want to fix one type of keystone because either you don’t have any edges in one of the axis to base the corrections on or your photo is already straight. Fortunately, you can choose that option by long pressing on the Keystone button until the little menu comes up. Then, select the option you want. From that point on, it works just like to regular Keystone tool. Be aware, that can’t correct the vertical lines with Keystone Vertical and then switch over to the Keystone Horizontal and correct the other type of lines as it will erase the previous (Keystone Vertical) corrections. You need to use the regular Keystone tool.
So that’s pretty much the Keystone tool in Capture One Pro. It’s really one of the tool that makes C1P as advanced as it is. Honestly, if it did not had that feature, the software would not be so much valuable as it is to me. I hope you learned something today!