James, auto-correction is always a bit of a gamble, but I believe, instead of trying to autocorrect in other photo editors you might be just as quick remaining inside Nitro… no, I just tried, sorry. Phew.
The problem with 4 point perspective corrector is that you really need to know how the new perspective should look like before your start it. In most other apps I align two construction-lines along two lines in the image which should be straight, either upright or horizontally. This is a lot of try & error in Nitro and the fact, that a portion of the image is enlarged massively and I first need to correct “enlargement” makes it less useful than most other competitors.
It’s not always about rectangularity in the image, depending on my perspective towards a facade. And cropping away huge chunks of the image which are outside the field of the perspective corrector makes the result (too often) useless. This looks like a lot of work needed.