Radial masks stay round when image is transformed (perspective correction)

Forum|Forum|1 year ago
June 14, 2024
3 replies
488 views

I am just checking out how much distortion my 16mm lens and camera tilt angle are producing. I placed circles on a wall. I used the radial mask to make perfect circles for comparison. When I transform the image (perspective correction), the radial mask stay circular, incorrectly. The blue circles are all the same size initally. The orange circles are all the same size initially. After transforming, the radius does vary as expected..

Lightroom 13.3.1

Mac OS 14.5, Macbook Air, M1 chip

As shot (tilt 12 degrees down)

Corrected perspective. Look at the lower lright circle in particular.

Way over corrected. The radial masks are still circular. Look at the lower right one agained.

macOS

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Bob Somrak

Legend

A poor functionality in Transform is the Radial Filter does not rotate when you use Rotate in Transform. Rotating a Radial in Transform/Rotate should be easy to implement as it should be mathematically the same as just rotating the Radial in the Masking Tool.

M4 Pro Mac Mini. 48GB

Bob Somrak

Legend

The Radial Filters are actually Ellipses. A circle is a special type of ellipse. To correct for the tilt the shape would have to become egg shaped so can not be represented by an elliptical Radial so LrC keeps the Radial the the same shape as before the Transform. You should Transform before using the Radial. This is as designed.

M4 Pro Mac Mini. 48GB

T

TanyaThreeAuthor

Inspiring

For most people, the masks staying circles (in my first post) is good enough. In the second post, the elongaged ellipse is really outside of an acceptible range. The nice thing about LR is that [for 99% of the time] it doesn't matter in which order you do the panels in. The only other case I can think of is AI masks like Sky and object removal. Anyway, that 1% is confusing.

The brush mask stuggles a bit, but less than the radial mask. The object selection mask is perfect when transformed. The radial mask does not behave like the other masks. Avoiding egg shapped masks was an unfortunate design choice.

T

TanyaThreeAuthor

Inspiring

Here is a an example that is more obvious - an oval radial mask along the diagonal really does not transform as expected:

I don't know if the shape is the same, but the mask is way too large in the transformed virtual copy.