Keystone – 80 % vs. 100 % correction

Capture One Pro 6 has a very strong and efficient Keystone Correction tool.

Keystone correction is made super simple by the use of the 3 different Keystone correction cursor tools:  Keystone Vertical, Keystone Horizontal and Keystone.

When using the Keystone cursor tool, the image will be corrected for both Keystone as well as any horizontal or vertical misalignment.

Capture One Pro 6’s method for correcting Keystone is mathematically identical to how an image would be corrected if it was shot with a technical camera.

When using the Keystone Vertical cursor tool for correcting the keystone of a building shot from below, Capture One Pro 6 will automatically set the amount of correction to 80 % and not 100 %. The 80 % correction looks more natural to the human brain than the 100 % correction.

The images above are three versions of a building shoot from below. The 80 % correction, automatically set when using the Keystone Vertical cursor tool, makes the building look straight while the 100% correction makes the building look wider at the top than at the bottom.

Use Keystone Correction at 80 % to achieve a natural look

If the image above had been shot with a technical camera with an ideal lens pointing horizontally, the image would be identical to the rightmost version with 100 % correction. In this version, the height of each window in the building are exactly the same and this confuses the brain, as we expect the windows to look smaller and smaller the further away they are. In the middle version with 80 % correction, the height of the windows look just a little bit smaller the further away they get. This is just enough to allow the brain to accept the building as looking naturally parallel and seen from below.

If you shoot a building from a position where you are able to point your camera almost horizontally, then you may want a 100 % correction.  You can still use the Keystone Vertical cursor tool, but you will need to change the default 80 % correction in the tool to 100 %.

How to use the Keystone cursor tools:

Step 1: Select the Keystone Vertical cursor tool from either the Keystone Correction tool or from the general cursor-tool toolbar. 

Step2:  Align the vertical guides with the vertical lines in the building. To obtain better precision, you can use the scroll wheel on your mouse to zoom into and out of the image while aligning the guides.

Step 3: Press the Apply button and the image will be corrected. Notice that the Amount slider has automatically been set at 80%. Also notice that the image has been rotated, as the camera was not perfectly aligned horizontally.

When using the Keystone cursor tools Keystone Horizontal or Keystone then a 100 % correction is used as this often makes more sense for these kinds of corrections.