Tuesday, February 06, 2007

02/06/07: What is Rectilinear Correction?

Rectilinear Correction

Rectilinear refers to straight lines that appear straight with no curves. Many wide and ultra wide angle lenses as well as all fish-eye lenses will bend straight lines. Sometimes this is done on purpose for creative affect. Other times the bend toward the edge of the image just looks wrong -- especially when people appear in the edge of an image.

There are several ways to correct this. You can either spend the big bucks and purchase an aspherical wide angle lens so that all lines appear straight, you can buy special software plug ins for your image editing program (click here for software solutions), or you can simply crop the image so that the annoying element at the edges is removed (which won't correct lines in the middle that appear to have a bend to them, but it can remove destracting overly-exaggerated elements at the edge of the wide or ultra-wide angle image).

Here are two images that show the same scene with and without rectilinear correction. Both images were created with a Canon 5d (full frame sensor) digital SLR.

(above) Canon 15mm fisheye lens - not rectilinear corrected

Canon 17-40mm (at 17mm) - rectilinear correct

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