Keystone correction

For an in-depth tutorial on how to use Keystone corrections, see here.

It is not always possible to get the best angle on a subject and eliminate all distortion. Architecture photographers often have to correct the perspective distortion of tall buildings. Capture One Pro gives you the ability to apply keystone correction. You can quickly correct any perspective distortion by using the vertical and horizontal sliders or using the cursor markers to pinpoint lines that should be parallel.

Keystone Tool with a new user interface is introduced in Capture One 22 (15.2.0). The content of the Keystone Tool has been split into two tabs, Guides and Sliders. Guides offer fully automatic and guided keystone options, while Sliders offer manual adjustments.

The Keystone Guides have been redesigned to easily place them with greater precision. Additionally, the precision of the guides can be fine-tuned using the keyboard arrows when a guide is selected.

The Keystone Tool can help to achieve perfectly vertical and horizontal lines to give the image the desired perspective. It’s not always possible to capture the desired composition while keeping the shooting angle perfectly perpendicular to the subject. In situations where it’s not possible to achieve a perfect capture angle, lines that are parallel will appear non-parallel in the captured image. This is known as perspective distortion.

Keystone eliminates perspective distortion in images where lines that should have been perfectly vertical or horizontal are not parallel, making it impossible to correct with rotation alone.

The new adjustment Skew has been introduced in the latest (15.2.0) release to accommodate a wider range of perspective corrections.

Automatic Keystone

Capture One can automatically correct Keystone using image vision (AI). This method will detect all lines in the image, find the vanishing points, and make the correction based on the lines that have the same vanishing points.

How to use

Automatic Keystone is available from the Keystone Tool, using the Auto button. By default, Auto will only correct Vertical Keystone, ignoring all horizontal lines. If Horizontal or Full Keystone is required, the Auto Mode can be changed by selecting one of the other cursor tools. The change will be reflected in the icon in the Auto button.

If Capture One cannot find suitable lines for automatic correction, nothing will happen to the image when pressing Auto. If Full Keystone is failing, consider switching to Vertical Keystone and trying again.

Automatic Keystone can be applied to batches of images, making it easy to instantly correct large volumes of images. Remember to enable Edit All Selected Variants to make sure all images that are selected will be corrected.

The global Auto Adjust functionality has the option to include Auto Keystone as well. When including Keystone in the set of automatic adjustments, only Vertical Keystone is available.

Amount

When correcting Keystone, the default Amount is always 100%. This means that the result renders perfectly vertical and/or horizontal lines. In some cases, in particular, when capturing tall buildings, this might not be what is desired as the result can quickly look unnatural, and a reduction in the perspective correction is needed. Changing the Amount will change the total Keystone correction to anything between 10% and 120%.

Phase One IQ digital backs

Some digital backs from Phase One have built-in motion sensors to log the angle of the camera during capture. This makes it possible to correct the image to some degree, even if no visible lines are present in the image. Keystone correction using in-camera data is available from the Sliders tab, and will only apply changes if the raw file has built-in metadata available.

Apply keystone correction manually using Guides
There are three Keystone auto-correction tools denoted by the following icons from left to right: Keystone Vertical, Keystone Horizontal, and Keystone. The active icon will turn orange. The keystone correction tool can be selected using the keyboard shortcut K.

How to use

1. Go to the Lens tool tab.

2. Select desired Keystone type.

3. Set the four points to mark up the vertical or horizontal lines that need to be aligned.

4. Press the Apply button (located in the center of the image in the viewer).

NOTE: When a handle point is selected (orange circle) the handle can be moved with arrow keys. If holding Shift down (on Mac) the movement of the handle point is greater.

Amount set to 100% per default. After applying the keystone, the amount slider can be adjusted.

Apply keystone correction manually using Sliders

Keystone can also be applied by manually adjusting the 4 sliders: Vertical, Horizontal, Skew, and Aspect.

By dragging the Vertical, Horizontal, Skew, and Aspect sliders you can control the keystone effects in an image.  While dragging any slider, a grid is automatically placed over the image to help you align horizontal and vertical aspects.

Both vertical and horizontal keystones can be corrected. These corrections can be applied at the same time or independently from one another.

Press 'V' on your keyboard when finished to switch to the 'Select' cursor tool, which will allow you to easily see how your Keystone corrections will look once applied, without any Keystone grids or guides.

NOTE: In Capture One Express, the Keystone function is not present.

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