| 摘要 |
In a method for detecting impurities in a transparent material, the material (2) is scanned line by line and the light transmission through the material is measured and compared with a reference value. If the transmission value at one point of the material is in a predetermined relation to said reference value, indicating the occurrence of impurities, the light transmission is studied in an area around the measured point for this transmission value in order to determine the extent and shape of the impurity, the light transmission values in the central area of the impurity being compared with transmission values measured in surrounding parts of the impurity to determine whether the impurity is of gel type or an impurity of some other type. A system for detecting impurities in a transparent material, which system comprises a camera (6) arranged to scan the material (2) and register light transmitted through the material in the form of pixel values, and a first comparator (8) for comparing said pixel values with a reference value. If a pixel value is in a predetermined relation to said reference value, a signal processor (12) analyses registered pixel values from an area of the material around said pixel value in order to determine a centre for the impurity and compare pixel values in said centre with pixel values in the surrounding parts of the impurity to determine whether the impurity is an impurity of gel type or an impurity of some other type. |
