In this tutorial we deal with correct perspective a photo with Gimp. Often (especially in the narrow streets) having to take pictures of monuments or facades of tall buildings, having available a limited field for framing. It is clear that we will be closer to the monument over the photo will be “far” from being correct axonometric. The perspective correction is also called correction (or modification) the falling lines. This is because taking a photo close to an architectural element gets the impression that the monument is falling backward (the architectural lines converge upwards.
MathMap is a plugin for Gimp rather complex. Can also be used as a stand-alone command-line, but of course it is easier to use with Gimp because of the graphics facilities that follow. Unlike MathMap FX-Foundry is a plugin much more primitive. Creates an entry in the main menu and special deals only speed up some operations already feasible with Gimp, but that would cause us to lose time.
We find the filters MathMap below “Filters” – “Generic” – “MathMap“, and filters FX-Foundry in its menu (on call to bar menus).
First we take a picture that lends the work. Transform the first photo, and the final result is the following:
The first thing we must do is correct perspective. Let's go over “Filters” – “Generic” – “MathMap” – “Distorts” – “Bilinear interpolation“.
Let's go under the tab “User Values” and move the value “a3” trying to verticalize as much as possible the lines.
Now we'll have to cut off le zone “Empty” image with the instrument “Cutter” .
And now we will give a cut to the next step by adding the authentic vignetting. “FX-Foundry” – “Photo” – “Effects” – “LOMO Effect“.
At this point in the tab “Levels” reduce the opacity vignetting of the 50%, so we get the final result.
This tutorial is for the sole purpose of show how to correct the perspective of a photo, we must not forget, however, that photography is art. If a picture we like it like no one forces us to correct colors, the’exposure o la outlook. It all depends on the outcome we want to achieve.