CORRECTING TILTED PHOTOS
(This article originally ran in the December, 2010 Digital Horizon column in Railfan & Railroad Magazine.
It has been updated for presentation here.)


Original, tilted image.

After correction in Photoshop.

A tilted image can occur if you are not careful with your composition when taking a photo. Such was the case with the accompanying image above of a Kansas City Southern train running with a Norfolk Southern C40-9W as lead power crossing the Ouachita River bridge in my home town of Monroe, Louisiana, in 2001. I was fascinated by the design elements of this 100+ years old bridge’s latticework of steel beams, on this former Illinois Central Gulf (later RailSouth Corporation) line from Shreveport across north Louisiana into Vicksburg, Mississippi, but wanted to photograph the bridge with a train present.

I had gotten into railfanning only after moving to Colorado so never got the idea of making this shot until on one of my annual visits back to Monroe. On those trips, whenever I had the time and I knew it was likely a train might be crossing the bridge, I would drive over to this location in hopes of catching a train without having to wait too long. Often I was too late to catch a train, or ended up waiting in vain for a train that never arrived, or the light was wrong. This time, I “nailed” the time of my arrival a little too closely. I saw this train approaching as I drove up, and barely had time to get into position to take a shot. The hurried effort resulted in a slightly “leaning” composition.

If this shot had been on a slide, I would have been stuck with the tilted image. But now digital imaging allows an easy correction, either from a film camera image or digital camera image. This can be accomplished in two ways, by using either a “rotate” or a “skew” function in an image editor, after first scanning in the slide or negative, or direct from a digital camera image.

Rotate: Pull up the image in your image editor (PhotoShop was used for all the adjustments described here, but PhotoShop Elements and other programs have similar functions) and re-save as a different name, to preserve the original in case you mess up the correction. Next, rotate the image to the degree that the leaning lines return to vertical (or horizontal). In PhotoShop, the procedure is IMAGE > ROTATE > ARBITRARY and set the rotation to the degree appropriate to get the image back to where it appears straight. In Elements, the procedure is slightly different: IMAGE > ROTATE > CUSTOM.

This can be a trial and error process so if a certain degree of rotation does not completely straighten the image, or over straightens, hit EDIT > UNDO and try again.

Once leaning lines within the image look appropriately vertical or horizontal, crop to eliminate the now “lopsided” edges to get the final rectangle image, and save. If you no longer want the original, tilted image, you can resave this corrected version with the same name as the original, then delete the image file you resaved to start this process. This avoids gunking up your computer with unnecessary or extra copies of the same image.

Skew: You can also adjust the edges of the image until vertical or horizontal lines within the image straighten up. In PhotoShop, go to IMAGE > CANVAS SIZE (not “Image Size”) and add a couple of inches of blank, white canvas around the image. Draw a selection box around the image (not including the blank canvas area). Next, go to EDIT > TRANSFORM > SKEW (or DISTORT). In Elements, use IMAGE > ROTATE > CANVAS SIZE, then IMAGE > TRANSFORM > SKEW (or DISTORT).

Little square “handles” will appear on the corners of the image selection. Placing the cursor on one of these handles at a time, “drag” the side of the image into a correct alignment where straight lines within the image (such as the edge of the locomotive) are not leaning. In either PhotoShop or Elements, you can also choose FREE TRANSFORM rather than SKEW or DISTORT and while holding down the Ctrl key, drag the handles to get the same adjustments. Be careful to not skewer or distort the edges to the point the photo looks too distorted (“fat” or “skinny”), which is easy to do. You will probably have to play with each edge until the vertical or horizontal lines in the image all look correct. Once the image looks right, crop to eliminate the added canvas size, and save the final image.

These techniques can also be used with a horizontal, scenic type composition with a train stretched out horizontally that has a tilting horizon.

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