Photoshop tutorial: converging lines

Oh no, the building is tipping backwards or looks tilted in the landscape! So-called converging lines cannot always be avoided when taking photographs. Wide-angle lenses in particular produce small optical faults of perspective. We will show you how you can easily straighten up your pictures in Adobe Photoshop.

Converging lines occur as soon as the camera is not aligned parallel to the object. This effect occurs most frequently with buildings, because photographers are forced to tilt the camera upwards. If they kept the camera parallel to the ground, they would avoid converging lines but would only have shots of the ground floor. Architectural photographers therefore use Tilt-shift lenses with special functions which already correct the optical effect while the photos are being taken.

There is also software, however, with which you can correct the converging lines after shooting. Adobe Photoshop is one of the most widely used applications. Since version CS2 it has provided the option of correcting distortions. You can find this useful option in the menu under Filter > Distortion Filter > Lens Correction (since CS5 in the higher level filter menu). CS6 even includes a new adaptive wide-angle correction. It recognises the common types of camera, lens and functions almost automatically.

It is always useful to turn your photo into a "smart object". To do this, first of all open the picture to be processed and right-click on the button Levels. In the selection that now appears you will find the option "Convert into smart object". You can now edit and save your photo several times without sacrificing quality. Alternatively, you can produce a second level and so always switch between the original and the processed version. With the above-mentioned "Lens correction filter", various adjustments can be carried out very simply.

If you have skewed lines in the picture which should actually be horizontal, it is recommended to select this line with the "straightening tool". The result is immediately visible. Repeat the process until you are satisfied. It is now advisable to superimpose a grid (option at the bottom edge of the screen) and to align this along the converging line with the "grid shifting tool". You can now experiment with the settings a little until the desired result is achieved. In addition to straightening out the skewed lines, you can also use this filter, for example, to rectify horizontal and vertical errors of perspective, fix chromatic aberrations or stop pictures being warped.

Using the menu Edit > Transform > Perspective you can move the picture very simply with the "handles" in the corners of the picture, until here too the desired effect has been achieved. The converging lines are quickly rectified with this method, but the process often has a negative effect on the proportions. You can avoid this by selecting the second step Transform > Scale. Now pull the middle handle back into the position of the original picture. But be careful: because transforming involves a complete recalculation of all pixels it can lead to a small loss of quality.

Regardless of the method that you choose, it may be the case that the format is no longer completely filled. Here you need to weigh up the alternatives. You can simply cut the picture to size, but if, for example, only a piece of sky is missing, you can complete this by retouching the image.