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Let X be an affine space over a field k, and V be its associated vector space. An affine transformation is a bijection f from X onto itself that is an affine map; this means that a linear map g from V to V is well defined by the equation () = (); here, as usual, the subtraction of two points denotes the free vector from the second point to the first one, and "well-defined" means that ...
Equivalently, affine shape adaptation can be accomplished by iteratively warping a local image patch with affine transformations while applying a rotationally symmetric filter to the warped image patches. Provided that this iterative process converges, the resulting fixed point will be affine invariant.
Image registration algorithms can also be classified according to the transformation models they use to relate the target image space to the reference image space. The first broad category of transformation models includes linear transformations, which include rotation, scaling, translation, and other affine transforms. [5]
Image warping example. Image warping is the process of digitally manipulating an image such that any shapes portrayed in the image have been significantly distorted. Warping may be used for correcting image distortion as well as for creative purposes (e.g., morphing [1]). The same techniques are equally applicable to video.
The suite provides a number of programs for image registration with different transformation models, such as rigid-body, affine and nonlinear warping. For example, for affine transformation the registration from one brain scan to another may be found with the alignlinear program and written to the special air-file that stores the transformation ...
The simplest application of image geometry correction is a specific case known as keystone distortion correction derived from Keystone effect.Keystone distortion gets its name from the symmetric trapezoidal distortion resulting from misaligned projector placement in the vertical dimension (although the term is generally applied to the non-symmetric quadrilateral shape that occurs from an off ...
This method is also well suited for rendering quad primitives rather than reducing them to triangles, which provided an advantage when perspective correct texturing was not available in hardware. This is because the affine distortion of a quad looks less incorrect than the same quad split into two triangles (see affine texture mapping above ...
In the fields of computer vision and image analysis, the Harris affine region detector belongs to the category of feature detection.Feature detection is a preprocessing step of several algorithms that rely on identifying characteristic points or interest points so to make correspondences between images, recognize textures, categorize objects or build panoramas.