A method for measuring the dot area of ​​a lithographic printing plate

Abstract

The invention discloses a measuring method for printing dot area of lithographic printing, and solves problems that an existing measuring method is high in error and high in cost of measurement in the prior art. The measuring method includes utilizing a photomicrographic apparatus to take a picture for dot area and blank area on a flat printing plate to acquire digital images; eliminating affection of lighting unevenness by superposing negative films of the digital image of the dot area and the digital image of the blank area; binarizing the images by means of threshold segmentation, eliminating noise by means of expansion and corrosion, extracting five dots from the middle position of the binarized image, determining grid area by calculating distances among center points of the dots, and finally calculating the proportion of the dot area to obtain the dot area of the region. Plate information is acquired by universal equipment, results meeting requirements are calculated by an all-purpose computer, people do not need to manufacture special equipment, production cost is low, error caused in shooting is corrected by means of image processing, and measurement precision is high.

Description

technical field [0001] The invention belongs to the technical field of printing and relates to a method for measuring the dot area of ​​a printing plate of lithographic printing. Background technique [0002] Offset printing uses dots to reproduce the tone and color of the original manuscript, and the dot size plays a decisive role in the printing quality. The printing plate production method currently used in production is to use the computer to complete the rasterization process of the large-format file, and then use the computer-to-plate equipment to directly expose the image on the printing plate, or use the laser phototypesetter to output the film first, and then pass the close exposure. way to transfer the image onto the printing plate. Due to many factors such as voltage fluctuations, aging of the laser generator used for exposure, or changes in developing conditions after exposure, the dot area of ​​the finished printing plate may change, which will affect the final...

AI Technical Summary

Problems solved by technology

At present, one method of measuring the dot area of ​​the printing plate is to use a densitometer to measure the density of the blank part and the dot part, and then calculate the dot area. If it is too small, the calculation of the dot area by measuring the density will produce a large error, which cannot meet the needs of production; another method for measuring the dot area of ​​the printing plate is to make a special printing plate detection device, and the built-in image sensor captures the image , and then the dot area is calculated by the built-in image analysis software, but this method has high requirements on the accuracy of the image sensor, making the manufacturing cost of the instrument high

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