February 27, 2010
2 Comments
Mayzie

Lens Correction In Maya

In real life, some photographic lenses on certain cameras can move horizontally and vertically in order to control what’s known as the Key-Stoning Effect. We can correct this in post-production apps such as Photoshop but this introduces a number of problems that are just not worth it in the end.

Luckily, we are able to control this effect directly in our cameras within Maya.

The Problem

A focal length of 14 produces a noticeable Keystone Effect

The reason why we want to “remove” the key-stoning effect is because when using wide lens angles (such as Focal Lengths of 14 or 16) a phenomenon occurs where the lens can make a subject look as if it is “falling over”.

The Solution

The Keystone Effect is reduced in this shot, however it is best not to eliminate it completely otherwise the subject may appear to "fall-over" in the opposite direction to what you were originally trying to correct

The idea is to correct the converging vertical lines into near perfect parallel lines which reduces this effect of “falling over”. It is best to avoid a picture with perfect parallel lines as what we are correcting is really a natural effect, it can just be too distracting in certain shots like the picture above.

The Vertical Film Offset Attribute

If you follow these steps you should be able to tweak and reduce the Keystone Effect until your shot looks more natural:

1)	Turn on the Resolution Gate
2)	Aim the Camera at the horizon or close to the horizon
3)	In the Attribute editor, use a value of around .1, .2 or .3 in the Vertical Film Offset (Remember the first input box will control the horizontal value [x], the second input box will control the vertical value [y]
4)	Adjust this value until your subject appears back in the Resolution Gate

You may have to aim your camera above or below the horizon depending on your scene, but if you control both this and the Film Offset value on your camera you should be able to completely control and reduce the Keystone Effect with Maya

Note: In V-Ray for Maya you have the option to use the Lens Shift option the V-Ray Physical Camera, however the visual feedback for this setting is not available in Maya’s viewport, therefore it is recommended to use the Film Offset attribute instead.

More Examples

You can even still see the effect in the following interior renders

The columns in this building appear to look slightly unnatural before the keystone effect is corrected in Maya

The Keystone Effect is slightly reduced in this shot

I should also mention that you can also use the Film Translate value in the camera, however this is not supported by some 3rd party renderers for Maya, so instead I prefer to use the Film Offset value. Use whatever works best.

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