# Purpose and Principles ## Purpose Based on an innovative feature-point technology, **EasyFind** is a matching tool designed to rapidly locate one or more instances of a pattern in an image. With an adjustable accuracy up to sub-pixel level, it reports very precise information about the instances found, such as their location, rotation angle, scale and matching score.  * Fast Processing and Improved Robustness: **EasyFind** is based on a new feature-point technology. Instead of comparing the pattern to the sample image pixel-wise, it carefully selects relevant feature points in the pattern. This method allows **EasyFind** to match only the areas that convey valuable information, resulting in faster processing and much improved robustness. * **EasyFind** supports learn regions, a feature that allows the creation of complex pattern shapes. * **EasyFind** supports learning multiple patterns, a feature that allows the creation of patterns robust to differences in illumination or deformations. * Training on vector patterns: In this mode, the learning is done on collections of 2D geometrical shapes rather than on rasterized patterns. The learning model is constructed using the class [`EVectorModel`](../../../doxygen_cpp/classeVision_1_1EVectorModel.html) [_.NET](../../../doxygen_cs/classeVision_1_1EVectorModel.html) [_Python](../../../doxygen_python/classeVision_1_1EVectorModel.html) either by loading it from a `dxf` file or, programmatically, by using [`EShape`](../../../doxygen_cpp/classeVision_1_1Legacy_1_1EShape.html) [_.NET](../../../doxygen_cs/classeVision_1_1Legacy_1_1EShape.html) [_Python](../../../doxygen_python/classeVision_1_1Legacy_1_1EShape.html) objects. This extension is well-suited to find objects with a known geometry. #### NOTE In practice, you can assume an accuracy of 1/15_th pixel in position and 1/15_th of a degree in rotation. #### NOTE Compared to **EasyMatch**, **EasyFind** is computationally fast, robust against noise, occlusion, blurring, missing parts and illumination variations but only supports grayscale images while **EasyMatch** also supports color images. ## Principle * **EasyFind** uses edge feature points to find instances in a search field: - An **edge feature point** is an abrupt change of gray level between two pixels. - It indicates that there is an edge at this location in the search field. * To start the [`EPatternFinder::Find`](../../../doxygen_cpp/classeVision_1_1EPatternFinder.html#aeeb160cde9343ffc0d8583ac1d330e4d) [_.NET](../../../doxygen_cs/classeVision_1_1EPatternFinder.html#a9c35c544243729d9907eb708f7d2a0e2) [_Python](../../../doxygen_python/classeVision_1_1EPatternFinder.html#a44780e599d160cbb5f8e405042ace771) function, **EasyFind** needs either a pattern image on which it computes the edge feature points or directly a geometrically-defined feature model.  * To use this tool: - The patterns must be well contrasted with sharp edges. - They should be substantially different from the rest of the expected search fields. - They can be scaled or rotated. * **EasyFind** is very robust regarding: - Blurring - Noise - Occlusion - Illumination variation