Lens Distort

The Lens Distort tool lets you create or correct lens distortion that may be present in image sequences.

Barrel distortion is associated with wide angle (or minimal zoom) lenses. It causes the images to appear slightly curved outward like a barrel. You can notice this when you have straight features close to the image's peripheral sides.

The Lens Distort tool has the following parameters:

Use:	To:
Mode	Select either lens correction or distortion. This affects all other parameters. The other parameters will be considered either in a distortion or in a correction work flow. The distortion transformation is exactly the inverse of the correction, so keeping the same parameters and putting back to back distortion plus rectification will give back the original result, but filtered twice at each transformation resulting in possible degradation in image quality.
Magnitude	Set the first parameter (k1) of the lens distortion equation: rd = r + k1 * r^3 + k2 * r^5.
Adjustment	Set the second parameter (k2) of the lens distortion equation: rd = r + k1 * r^3 + k2 * r^5.
Anamorphism	Characterize anamorphic asymmetry. Note that this has nothing to do with the pixel aspect ratio of the captured image.
Center	Set the X and Y coordinates of the center of the distortion. Those parameters are expressed in pixels. The lens center can also be changed by clicking directly in the player. The center manipulator is always active in the player. The look of the manipulator is a cross. The cross can be manipulated by selecting it and moving it.
Height	To determine the region where the lens distortion or correction is applied. This parameter is initialized to the composition height.
Fit Source	To set the height input to the input height.This parameter is needed to be able to perfectly inverse a lens correction.

Expected Workflows

The following are common use cases for lens distortion or correction:

Footage to be used as a background layer has noticeable lens distortion and footage to be composited over the background does not. The Lens distort tool would be added to the dependency graph and used (in Correct mode) to rectify the distortion before compositing the new layer over it. The composite will then be made (any compositing operation) and a second instance of the correcting Lens Distort tool would be added after the compositing operation has taken place using the same values but in Distort mode applying the original distort to both layers.
Applying lens correction on multiple compositions before compositing them together.
Reproduce the lens distortion of one composition on another composition.
Using the tracking data from one composition and applying it to the center of another distorted composition, or composited layers, producing interesting animated effects.

Analysis of Radial Distortion

Analysis of radial distortion computes the magnitude and adjustment parameter from a three point spline created in the player to identify distortion. The analysis is only available when the lens mode is set to “Correct”. All parameters except the magnitude and adjustment are used to compute the new magnitude and adjustment. The magnitude input will be set at the current frame when the analysis is finished. Note that only one spline can be created at the time. The spline is not animatable.

To analyze radial distortion with the spline tool:

Set the Mode to Correct.
Draw a three point spline along edge of any distorted features within the image that should be straight. When three points are drawn, the select tool will be activated.
Modify the existing spline.
Click the Analyze button to analyze radial distortion from the created spline. The image is corrected and the Magnitude and Adjustment fields are updated.
To remove the spline, click Clear. Note that this removes the editable spline only, but does not remove the correction. If you add a new spline, corrections will be additive.
To begin a new analysis, click the Reset button in the Tools Options.
To correct an analysis, use Undo (Ctrl + Z for Windows and Linux or Cmd + Z for Mac OS).

Output

The Lens Distort tool has an Output tab with the following parameters:

Use:	To:
Crop	Change the size of an image—see Cropping and Filtering the Output.
Filtering	Smooth the transformed pixels—see Cropping and Filtering the Output.

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