Perspective correction in architectural photography

in Tutorials
By peterspiro/Peter (3,382) Send mail to this user on January 22, 2003 7:54:09 PM CST

Perspective Correction Using Software

When we look upwards to see the top of a building, our brains automatically compensate for the fact that the more distant top appears smaller. However, when the same thing appears in a two dimensional photograph, the building looks odd, as if it is leaning over backwards. The ideal would be to take the photo by locating the camera at a height half way up the building, but this is often not possible. One way to eliminate this problem is a view camera with a tilting front, or a perspective correction shift lens on a 35mm camera. These perspective correction lenses cost $1000 and up, and for some brands (such as Pentax) they are no longer even in production, and very hard to find.

I was pleased to discover that even the relatively simple software, Adobe Photodeluxe, that came bundled with my first digital camera, does a reasonably good job of correcting for this distortion.

Perspective correction can be done with both Photodeluxe and Photoshop Elements. It is not possible with Photoshop LE. (I have been told that it can also be done with Photo Brush and Panorama Tools, but I have not tried either of these.)

Before you start, it is best to go to the size option, and choose "enlarge canvas," which gives you blank white spaces into which you can stretch parts of the image.

In Photodeluxe you go to the "size" option on the menu bar, and then choose "perspective" within that menu. In Photoshop Elements you go to the "Transform" option which has "perspective" as a sub-option.

This gives you a box where you can compress the bottom edge of the picture or stretch the top to whatever degree you want. You simply do it over again until you get the desired amount of correction. You can also push one corner up more than the other, to get a trapezoidal shape, to correct perspective more on one side of the picture than the other.

The picture "canvas" you now have has slanted edges, and you trim it to get it back to a rectangular shape. If you did it by squeezing the bottom edge, you will end up with a picture in which the whole building is as narrow as the top was previously. This may strike you as being too narrow. In that case, you just go back to the "photo size" option, and stretch the picture horizontally (you do this by unchecking the "constrain proportions" box).

As an example of a picture in need of correction, I offer this one of the Parliament in Budapest. This is right beside the Danube River, and the picture needed to be taken with a 19mm lens pointing upwards.

Here is what it looks like after the first stage of perspective correction:

The final perspective correction job is my Photosig submission Parliament in Budapest.

When using Photodeluxe for this correction, straight lines sometimes develop slight jagged edges. It seems to have a somewhat inferior algorithm. This never happens with Photoshop Elements, so if you have it, it's the preferred tool to use.

Please visit my Photosig portfolio by clicking here.


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