The paper considers the problem of images cropping obtained by projective transformation of source images. The problem is highly relevant to analysis of projective distorted images. We propose two cropping algorithms based on estimation of pixel stretching under the transformation. The algorithms use the ratio of pixel neighborhood areas and the ratio of their chord lengths. The methods comparison is conducted by estimation of cropped background relative areas. The experiment uses real dataset containing projective distorted images of the pages of Russian civil passports. The method based on chord lengths ratio shows better results on highly distorted images.
In this paper we present two algorithms modifications of projective-recognition of the plane boundaries with one concavity. The input images are created with orthographic pinhole camera with a fixed focal length. Thus variety of the possible projective transformations is limited. The first modification considers the task more generally, the other uses prior information about camera model. A hypothesis that the second modification has better accuracy is being checked. Results of around 20000 numeral experiments that confirm the hypothesis are included.