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Cylindrical Unwarp

The Cylindrical Unwarp module performs an unwarping operation on an image in order to remove warping on the sides of an image. This warping is caused by lens distortion that causes objects towards the edges of an image to become stretched. This unwarping operation is needed for panoramic stitching or for consistent measurements of objects near the edges of images.

The module is used in cases of panning the camera should match with previous images during the pan. Note that this module only affects movement in the horizontal direction and does NOT work with vertical movements. If you need vertical warp see the Spherical Unwarp module.

Interface

Instructions

1. Curvature - Specifies how much curvature to introduce to the image left and right edge in order to correct for stretching of images due to lens distortions. Use the slider or up/down buttons to warp the image into correcting edge stretching. By ensuring that horizontal lines in the image remain horizontal towards the edges will help to correct for this form of distortion.

2. Center - The horizontal center of the transform. This helps to correct distortions that are offcenter from the middle of the image. Often the lens is not perfectly centered on the CCD which would cause the distortion to be off-center. By correctly aligning the transform the edge warping will shift and will become more consistent.

3. Rotation - Corrects for rotation of the CCD such that panning motion causes horizontal motion to remain horizontal. Note that the module is configured for -45 to 45 degree rotation as most CCDs are only misaligned by a few degrees.

4. Grid Size - To help you view how the warping adjustments affect alignment you can use the grid to better understand what numbers to use.

5. Crop - To remove the black borders around the image you can select the Crop checkbox. This will crop the image to the point that no black edges exist. Note that this changes the image size and removes pixel data that is otherwise correct.

Example

Source Images


Overlayed without Unwarp


Overlayed with Unwarp

See Also


Bottle Unwrap
Radial Distortion
Fisheye Transform
Polar Transform


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