Perspective correction using Microsoft Image Composite Editor

A prior post here showed how to use Microsoft Image Composite Editor, “ICE”, to make perspective corrections to panoramas (Perspective correction for panoramas). How do you make a perspective correction in a single photo? ICE, after all, is a compositing, stitching program and will give an error message when you try to load just one photo.Perspective distortion

If you do not have access to a full-fledged photo editing program, you can still use the free Microsoft Image Composite Editor to do that job.

ICE requires a minimum of two photos to operate. For stitching photos together, it’s primary purpose, the images must overlap so it can find the matching areas and combine the photos into a large composite.

Can it handle photos that overlap completely? Yes, it can. So a photo plus a copy of that photo fulfill the requirement of two images. It just so happens that there is 100% overlap. ICE can handle that.

loading photos into ICE

So, starting in Live Photo Gallery, make a copy of the photo you wish to correct. Select both the original and the copy. On the Create tab click More tools, then click Create Image Composite.

(If you do not have ICE installed this will not work, of course. Download ICE from the Microsoft Research Image Composite Editor download page.)

Live Photo Gallery starts ICE and loads the selected photos.set camera motion

In ICE the two photos will be recognized as “Planar Motion 1” for camera motion in the Stitch box (lower left). Set this option to Rotating Motion, see the illustration here.

Once this option is set, the menu bar above the image will show a little cube. Click that cube. An additional control will be added, “Projection”. In this control you can select how the image is to be translated. It will already show “Perspective”. The other projection options, cylindrical and spherical, are not applicable to this use. We want to make a perspective correction.

set projection

When a photo is taken of a building, or other subject, with the camera titled up or down to get the whole object into the frame, the resulting photo will show strong converging lines. The building, see photo higher up in this article, looks like it is falling in on itself. We call it perspective distortion, but it is how the camera sees the world.

This is a natural consequence of how optics works. Things farther away look smaller, hence the result. This also happens in our eyes. But we humans have a powerful built-in computer – our brain. We know the flagpole stands up vertically and that the walls of the building are vertical. When we stand in front of the building we do not perceive the converging lines, although we see them exactly the same as the camera.

In a photo, however, these converging lines look all wrong. Hence the need for perspective correction. The Image Composite Editor makes this correction easy. Just drag the image up or down, even side to side.

Microsoft Image Composite Editor

As you drag the image, ICE “distorts” it to modify the perspective. Moving the image up stretches the top out. You can move it sideways and the image area will be stretched appropriately. You can see this in real time so this process is very easy.

When you are happy with the result, click Apply.  You can then select the output file format and other parameters in the Export block. The Export to disk button initiates the file save procedure.

One bit of caution: You can make the perspective correction “perfect” so that all vertical lines will be truly vertical. When you look at that picture, however, it may not look perfect at all. It may, in fact, appear that the building is now out of proportion and “growing” outward at the top. Here are a couple of images of the building shown at the top. One is completely corrected, the other still has some converging lines. You will likely agree with me that a bit of under correction produces the better result.

Full perspective correction some perspective under-correction

Click on the photos for larger views.

.:.

© 2012 Ludwig Keck

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