<title>Evaluation procedure for imaging in web inspection</title>

Abstract

Experience from actual web inspection systems has shown that the quality of the image is crucial for the performance of the whole inspection system. Even the most sophisticated image processing methods or computer hardware cannot compensate for low quality images. In this paper the key characteristics affecting the image formation and test set-ups to measure the numerical values of these characteristics are introduced. The determination of the imaging properties is based on imaging known test targets and subsequent image analysis. Modulation transfer function, vignetting, noise and pixel-to-pixel non-uniformity values for typical image forming systems are given. The sensitivity of these characteristics is estimated by measuring their numerical values as a function of some key imaging parameters like f-number or the spectral range of illumination. The information content of defective surface samples picked from a steel manufacturing process is compared to the results of the test set-up measurements to demonstrate the relation between the quality of the image formation in web inspection and the measured imaging characteristics. As a conclusion, an image formation evaluation procedure is proposed. The possibility to optimize the performance of the image formation using the information from the evaluation procedure is discussed.

Method for evaluation of imaging in automated visual web inspection

“…18 For the camera type used in this study the specified PRNU is around 16% ͑peak to peak͒ at maximum. This was done by subtracting from every line in the image the average of 128 lines from an undamaged area in the image.…”

“…In the papers of Laitinen and Moring 18,19 an evaluation procedure for imaging was proposed. It is the aim of this paper to examine more thoroughly the special requirements for the imaging in web inspection and the theoretical bases of the modulation transfer function ͑MTF͒ measurement for a sampling imaging system.…”

Dynamic range in automated visual web inspection

“…The proposed methods concentrate on the determination of the spatial resolution and factors affecting the dynamic range are only briefly discussed in one paper. 2 It is the objective of the present research to form a basis for the analysis of the dynamic range of a web inspection system and to complete the methods previously proposed for the evaluation of the imaging.…”