Have you ever taken some great shots of buildings only to be disappointed by parallax turning them into wedge shapes, rather than the straight, square buildings that we perceive when we actually see them? This is one of the problems that affects photography, where the “truth” of what the camera shows differs from what we actually saw or perceived when we were there. A lot of our battles in photography, and our post-processing work come down to massaging the images we recorded with our cameras so they more closely match our perception of reality that our mind constructed when we were there.
In the case of parallax, one way to correct these problems is to buy a tilt-shift lens, like the Canon TS-E 17mm, 24mm, 45mm or 90mm but they cost somewhere between £1000 and £2000, so they’re probably only really practical for professional architectural photographers. Fortunately, we can also correct our photos in post, at the cost of some final resolution. In this video I use dartable, an open source photography workflow application and RAW developer. I do a quick raw edit of a wedding photo, correcting architectural perspective caused by tilting of the camera. I use the current development version of darktable (1.3+821).