Rectangular seal positioning method and device aiming at certificate image

Abstract

The invention discloses a rectangular seal positioning method and a device aiming at a certificate image. The method comprises the following steps of: S1, sequentially judging whether a color of each pixel in an original image is the color of a specified seal, and generating a binary image of original image; S2, generating an edge binary image based on the binary image; S3, setting a window, judging whether a total amount of a foreground ponit in the window in the edge binary image is less than a preset noise threshold, if so, moving the window to rejudge in the edge binary image, if not, calculating a center of gravity of the foreground ponit, and determining whether the centre of gravity is within a preset area, if so, determining that positioning is carried out successfully, and recording the edge binary image in the window, if not, moving the window in the edge binary image and rejudgeing. According to the method and device, some characteristics of a seal image are considered, a foreground image with a specified color is extracted, and the window is set to slid to intercept a rectangle to initially judge a position of the rectangle in the whole image, so that rectangle detection aiming at the seal image in a later period can be carried out within a small scope, and probability of false detection and a calculated amount are reduced.

Description

technical field [0001] The invention relates to the technical field of image recognition, in particular to a method and device for detecting a rectangle of a stamp image. Background technique [0002] There will be stamps of various shapes and sizes in the voucher image. In the processing of the voucher image, it is necessary to use various shape detection methods to detect whether there is a stamp of a specified shape in the voucher image. In addition, while detecting, it needs to be distinguished from seals of other shapes. Among them, the rectangular seal is difficult to detect because of the uncertain rotation angle when stamping. [0003] Since a rectangle cannot be expressed by a single analytical formula like a circle, in the current general shape detection method, the detection of a rectangle must first be detected by a straight line. Generally, rectangle detection can be summarized as the following steps: [0004] First, extract the edge map. Edge detection oper...

AI Technical Summary

Problems solved by technology

However, in the application of seal detection, the length of the rectangular edge segment itself has certain limitations. The method of voting separately and connecting straight lines in multiple sub-images will cause the rectangular edge to be missed, and the rectangle cannot be detected.

[0012] In addition, in the seal image, the rectangular shape feature is easily destroyed

For example, due to the smearing of the stamp, the abrasion of the stamp itself, etc., the rectangle in the image will have rounded corners and incomplete sides, especially the short side of the rectangle is prone to incompleteness

For these pictures, when Hough votes, there will be too few votes on the short side, resulting in missed detection of straight lines. If the threshold setting is changed, non-linear lines will be falsely detected as straight lines.

Then the method of extracting four peaks after Hough transform will cause inaccurate detection because the two peaks corresponding to the short side do not appear.

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