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Fri, Oct 12, 2018 7:17 AM


Straighten an imagen when there's no line that should become horizontal or vertical

Currently, when you want to use any of the tools Photoshop offers for straightening (ruler and crop AFAICT), you depend on the photo having any lines that are supposed to become horizontal or vertical.

Now, let's take this image as an example.

Like the vertical edges of these buildings, it's a very typical scenario that due to the perspective, none of the objects' edges will ever be vertical, as they will be converging on the image's vanishing point(s).
This makes all of the currently available straightening tools useless, except in the improbable case that there's a vertical or horizontal line going right through the very center of the photo.

Now, my suggestion in these cases is that Photoshop allowed us to indicate two lines that are theoretically vertical (not meaning they will ever be in the image), such as the edges of any two buildings in this photo (the further apart the better).
The straightening algorithm should then prolong said two lines until the point where they meet (probably well outside of the image), and rotate the image by the necessary angle to make the intersection point fall within the image's vertical axis.
If dealing with horizontal lines, the intersection point should be made to fall within the horizon line.

By default, said rotation could be performed around the image's center point but, for the sake of flexibility, an anchor point could be presented, to offer the possibility to customize the rotation if need be. In particular, when working with horizontal lines, this point would be used to adjust for the height of the horizon in the picture.
In the case of the photo having two horizontal vanishing points, such adjustment could be avoided by allowing for the indication of two pairs of lines, each pair converging on one of the vanishing points, these two points inequivocally determining the horizontal.

Due to the two-step nature of the process, I envision this process as similar to the workings of the perspective warp tool, maybe even being viable for integration into it somehow.

Hope this makes sense and can be considered for inclusion in some not-too-distant future.



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