Difference between revisions of "Hugin Camera and Lens tab"
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Revision as of 11:23, 7 May 2007
The Camera and Lens tab looks a lot like the hugin Images tab, except that the lens settings can be edited here. As in the Images Tab, multi-selection can be used to change the parameters for multiple images.
Panorama Tools and hugin allow the usage of images shot with different lenses and settings inside the same project. Each image is associated with a lens number. All images that share the same lens number use the same lens type, and may be forced to share the same lens parameters.
The Load lens... and Save lens... buttons allow you to keep calibrated lens profiles. Once a set of lens parameters has been obtained through lens calibration it shouldn't vary much for future projects. The advantage of this is that if only positions are being optimised in the hugin Optimizer tab, then as few as two or three control points are needed per image pair.
TODO Load EXIF, New Lens and Change Lens...
The Panorama Tools lens correction model has enough parameters to model most photographic images, these parameters can be set manually here in the hugin Camera and Lens tab or calculated automatically in the hugin Optimizer tab.
The most important parameters are the Lens type and the hor. field of view. hugin supports the following projections in input images:
- rectilinear This is the projection used by most cameras. It keeps straight lines straight. The maximum horizontal field of view is 180 degrees (for an image of infinite size, that is).
- Panoramic is used by panoramic cameras, such as the Horizon, Roundshot and Spheron cameras. This projection is also called Cylindrical Projection.
- Circular fisheye This is projection is used by fisheye lenses. If the image is circular, or the corners of the image are black, use this type of fisheye lens. A circular crop in the Hugin Crop tab can be used for cutting away the edge borders.
- Full frame fisheye Exactly the same projection as above, but the crop option will crop to an rectangle instead of a circle. This should be used for full frame fisheye images.
After the lens type has been specified, an estimate for the horizontal Field of View (HFOV) is required. The HFOV specifies the horizontal opening angle of the image in degrees. Since most photographers are more familiar with Focal Length as a measure for the HFOV, it can be entered into hugin, and hugin will compute the HFOV from it. For this calculation the actual focal length and the crop factor of the camera are required. If the 35mm film equivalent focal length is known, a crop factor of 1 should be used.
Radial Distortion, Image Center Shift and Image Shearing
Usually lenses do not project images exactly according to the selected projection type, but suffer from distortions. In many cases the distortions are acceptable for single image shots, but they need to be corrected when stitching a panorama. The a, b and c parameters are used to remove that distortion. They are applied radially from the image center, which can be moved by changing the d and e parameters. These a, b, c, d and e parameters are the basis of the panotools lens correction model.
Scanned images might also suffer from image shearing. This can be corrected using the g and t parameters.
The distortion parameters usually vary with the focal length, and to a lesser degree with the focus. The link checkbox indicates whether the parameter is linked or not. A linked parameter is forced to the same value for all images with the same lens number. This is the default for the HFOV and distortion parameters. If a parameter is not linked each images is allowed to have individual values for the respective parameter. This is useful if a different zoom or focus setting has been used for some images. If scanned images are used, they are usually not perfectly centered, and each image should have individual d and e parameters.
hugin models the photometric parameters of a lens/camera combination in a similar way to the lens correction model for Geometric parameters. These parameters can be set manually here in the hugin Camera and Lens tab or calculated automatically in the hugin Exposure tab.
Exposure and Color