Professor Tips

3 easy steps to accurate perspective in your architecture images

Capture One 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’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 8 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.

nocorrectionNo Keystone correction

80correction80% Keystone correction

100correction100% Keystone 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.


Step 2: 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.

All the best,


The Image Quality Professor
The Image Quality Professor

The digital pioneer, Niels V. Knudsen, is Phase One’s Image Quality Professor and founder of the IQP blog. Moreover, he is responsible for breakthrough advancements in image quality both in Phase One’s medium format camera systems and in Capture One Pro.

Comments (9)

Warren Malvick

This is one of the more beneficial tips that you have made. I can’t always use my tilt-and-shift lenses when out n the field. I have a folder dedicated to all of your CO8 blogs that I save. As soon as I can install Mac OS X 10.10, I will upgrade to CO8.

David Grover

Good to hear it Warren!

The keystone correction in Capture One is very straightforward and easy to use for technical and architectural subjects where there are straight lines to use as a guide, but the method where you can “nudge’ vertical and horizontal corrections as well as rotation as used by PTLens (can I say that here?) is also very useful for less formal photos and I’d like to see it in Capture One one day.

David Grover

Could you not nudge the values in the Keystone tool in a similar fashion?

David Edge

One could nudge the tetrahedron, but it’s less intuitive and you have to press apply after each nudge – with the other tool it re-draws after each nudge.

David Grover

Hi David,

I am talking in the Keystone Tool itself. Nudging the Horizontal, Vertical, Amount and Aspect ratios.


Oops, sorry David. You’re quire right. Must pay more attention!

Hi David,

How can I change the default 80% correction in the tool to 100%, so that I get 100% each time C1 starts up?
Thank you!

That should be ‘Niels’ instead of ‘David’.