How do I make a perspective correction like this one with RT?

Forget the PP on this but I did some work on the original and tried to correct the perspective with RT and couldn’t match what was probably done with photoshop. This might be a feature request or maybe I am missing something.

Original

PP’d

I did manage to do something similar with Fotoxx but lost more. It did keep the building intact though. The top wasn’t chopped off. The shot shows a very common problem with wider angle lenses - the camera had to be pointed up. Fotoxx uses a click on 4 corners of a square but sometimes that isn’t easily possible. It offers several others corrections as well.

John

2 clicks in darktable :smile:

2 Likes

Moin @houz!

You forgot to tell us what two clicks!

1 Like

I guess he refers to A new module for automatic perspective correction | darktable. However, still not part of the released versions.

One slider move in RT. :sunglasses:


To get more sky you’ve have to set the crop by hand.


On the contrary… with a wide angle lens, you can shoot exactly horizontally and keep the whole building in the frame, and this will preserve the verticals. You will of course chop off the bottom half later. Yes, you waste pixels, but the interpolation done when fixing the perspective isn’t innocuous either (as anyone even done a blind test on this?).

With a longer lens you are more likely to be unable to shoot horizontally and therefore more likely to tilt the lens up and get perspective distortions.

So it’s not really a problem of wide angle lenses, but of the kind of pictures one does with wide angle lenses, especially when they aren’t wide enough.

Another solution is to use a tilt-shift lens.

On the contrary… with a wide angle lens, you can shoot exactly horizontally and keep the whole building in the frame, and this will preserve the verticals. You will of course chop off the bottom half later. Yes, you waste pixels, but the interpolation done when fixing the perspective isn’t innocuous either (as anyone even done a blind test on this?).

Not sure how quotes from posts work on here

However the reason the image turned out as it did is that there was insufficient space to keep the lens horizontal. I often find that to be the case on buildings and all that can be done is to keep it has horizontal as possible and also bear in mind the cropping that is likely to be needed.

John

:rage: So I have to guess a crop to bring the unseen part of the image in ??

I’ll try the steps ToWaBoo outlined but can’t say I am happy about it.

I’d did what most would do - adjusted the slider and thought oh no as the top features of the building were chopped off.

I do have the Fotoxx solution to that problem - uncropped - a wysiwyg one

True distortion correction can mess things up but often providing the corrections are fairly simple it wont matter at web size.

:grin: I messed with colour balance a bit but should have done more.

John

What @chris said.

You don’t have to guess. :slight_smile:

Activate “Crop” and move the border of the picture area (the cursor will cange). If you want to keep the aspect ratio, check “Lock ratio” and select “3:2”. To move the crop around, hold down the Shift key while moving the picture.

To quote text, highlight the text you want, then hover over it. A button labeled “Quote” pops up. Click “Quote” and the highlighted text is properly added in the reply box. If you need multiple quotes, make sure you pay attention to where the cursor is in the reply box.

Ahhhh. Got it. RT was defaulting to autofill - :blush: I should have noticed that from your first post.

John

Here was my geometry settings:

And how the crop looked:

To adjust the anti-barrel, I kind of split the distortion between the vertical lamp post on the right and the MILNE’S COLD STORAGE & ICE FACTORY lettering horizontal baseline.

1 Like