Digital Image Quality Analysis and Evaluation Research
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With the advancement of digital technology, the printing industry's acquisition of images has been completely digital. Traditionally based on physical and chemical imaging systems such as film and film, because of the high price, narrow application and low sales volume, manufacturers no longer have to launch corresponding high-quality roller scanners and large-format flatbed scanners. Instead, they are cheap and cheap digital cameras. The combination of digital back and mid-range small-format flatbed scanners is more flexible and applicable in practical applications in the printing industry.
Today's digital digital cameras, which are popular in mobile phones, have begun to enter the billion-pixel era. The digital imaging method will undoubtedly become the mainstream. The quality of digital imaging determines the quality of printed images from the source. . The acquisition of digital images and the replication process are in urgent need of establishing standards that make the quality of printed digital images linear, controllable, measurable and evaluable.
Image quality evaluation method
The evaluation of the quality of printed matter is the core evaluation standard for the quality of printing. The evaluation method of traditional printed image quality is based on subjective evaluation and supplemented by objective evaluation. The main method of subjective evaluation is to observe under the observation environment of standard light source; the objective evaluation method is mainly to use auxiliary instrument test data, and the objective evaluation methods for quality control in printing production are generally divided into three types:
1. Density method. The CMYK values are read using a Konica Minolta FD-7 densitometer or an X-Rite exact density meter. The color of the indicator points of interest in the screen is sampled and recorded in a database for numerical analysis, curve drawing, and scoring.
2. Spectrophotometry. The Lab value of the printed matter is read by an automatic test instrument such as X-Rite XRite intellitrax or Konica Minolta FD-9, and the numerical analysis score is performed. Among them, the Intellitrax has a larger measuring range, which can not damage the test sample, while the FD-9 has a smaller format.
3. Online detection (image method). The CCD camera captures the image and analyzes the RGB color values of the printed color blocks for judgment and analysis. This method is mainly used to find quality problems in the quality inspection process in time. Because the test instrument and software can work under continuous steady state, it is more reliable than manual detection.
Since the test principle of chromaticity and density is to test the comprehensive effect of a color patch area, sometimes it does not reflect the flaws in the details of the product. Therefore, the quality evaluation method based on image test is widely used, but the corresponding measuring equipment is generally expensive, printing The industry still lacks sufficient in-depth research and applications.
The evaluation of printing quality is still based on subjective evaluation as the highest principle, even if subjective evaluation can not adapt to the quality control of large-scale production.
Introduction to Imatest Image Quality Analysis Software
Imatest software is a digital image quality analysis software developed by American Imatest based on MATLAB platform. It has become the mainstream tool for digital image quality analysis. It is applicable to cameras, cameras, optical devices, printing and packaging.
The Imatest master software is used for static image analysis and can run on Windows, Mac and Linux platforms.
Imatest IT (Industrial Testing) is used for automated image inspection and production line online detection programming to call image analysis functions, supporting C/C++, Python, NET c# and other mainstream programming language calls.
The printing industry can use this tool, widely used by upstream digital camera manufacturers, for image analysis.
The image analysis module of the Imatest master software for the printing industry includes:
ColorChecker for analyzing image colors; Stepchart for analyzing tone (dynamic response range);
Uniformity for analysis of uniformity; Wedge for defect detection;
The Multichart module can analyze charts such as IT8.7 commonly used in print color management.
Combined with a colorimeter and a densitometer, automated analysis of multiple color data can be performed.
Digital imaging is gradually becoming the mainstream way of image acquisition in the printing industry. The quality of images is determined by the combination of lens, light source, shooting system and digital image processing software. The color management experience already in the printing industry cannot simply cover the imaging quality evaluation of digital imaging devices (such as HDR wide dynamic images).
The process of acquiring digital images in the printing industry lacks a reliable industry basis, especially for the reproduction of artwork such as murals. When we rely on digital cameras to acquire images, this shortcoming becomes prominent. The printing industry also needs to explore more ways to copy and evaluate digital images. Image quality evaluation can be re-developed with software such as Imatest, so that the quality evaluation of digital images conforms to international standards and the actual application of the printing industry.
Digital imaging is gradually becoming the mainstream way of image acquisition in the printing industry. The quality of images is determined by the combination of lens, light source, shooting system and digital image processing software. The color management experience already in the printing industry cannot simply cover the imaging quality evaluation of digital imaging devices (such as HDR wide dynamic images). The process of acquiring digital images in the printing industry lacks a reliable industry basis, especially for the reproduction of artwork such as murals. When we rely on digital cameras to acquire images, this shortcoming becomes prominent. The printing industry also needs to explore more ways to copy and evaluate digital images. Image quality evaluation can be re-developed with software such as Imatest, so that the quality evaluation of digital images conforms to international standards and the actual application of the printing industry.