Using Pythagorean triangles to approximate angles
American Mathematical Monthly
A fast algorithm for general raster rotation
Graphics gems
DCGA '96 Proceedings of the 6th International Workshop on Discrete Geometry for Computer Imagery
The Number of N-Point Digital Discs
IEEE Transactions on Pattern Analysis and Machine Intelligence
Scaling of plane figures that assures faithful digitization
IWCIA'08 Proceedings of the 12th international conference on Combinatorial image analysis
Computing admissible rotation angles from rotated digital images
IWCIA'08 Proceedings of the 12th international conference on Combinatorial image analysis
Hinge Angles for 3D Discrete Rotations
IWCIA '09 Proceedings of the 13th International Workshop on Combinatorial Image Analysis
3D discrete rotations using hinge angles
Theoretical Computer Science
An algorithm to decompose n-dimensional rotations into planar rotations
CompIMAGE'10 Proceedings of the Second international conference on Computational Modeling of Objects Represented in Images
Sufficient conditions for topological invariance of 2d images under rigid transformations
DGCI'13 Proceedings of the 17th IAPR international conference on Discrete Geometry for Computer Imagery
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Rotations in the discrete plane are important for many applications such as image matching or construction of mosaic images. We suppose that a digital image A is transformed to another digital image B by a rotation. In the discrete plane, there are many angles giving the rotation from A to B, which we call admissible rotation angles from A to B. For such a set of admissible rotation angles, there exist two angles that achieve the lower and the upper bounds. To find those lower and upper bounds, we use hinge angles as used in Nouvel and Remila [Incremental and transitive discrete rotations, in: R. Reulke, U. Eckardt, B. Flash, U. Knauer, K. Polthier (Eds.), Combinatorial Image Analysis, Lecture Notes in Computer Science, vol. 4040, Springer, Berlin, 2006, pp. 199-213]. A sequence of hinge angles is a set of particular angles determined by a digital image in the sense that any angle between two consecutive hinge angles gives the identical rotation of the digital image. We propose a method for obtaining the lower and the upper bounds of admissible rotation angles using hinge angles from a given Euclidean angle or from a pair of corresponding digital images.