| 摘要 |
The contrast determination apparatus includes illuminating light sources (12) and an image sensor (26) i.e. a 2-D CCD for capturing a two-dimensional image of e.g. a marked wire (32) on a holder (34), the captured image being sampled over the mark and the background. The sensor includes an optical system (28,30) selected with regard to the character size of the marks so that the field of view of the sensor is sufficient to contain a complete character as well as a generous amount of background. An area of the captured image is designated in which the samples for contrast measurement are to be taken, and a processor (24) takes the pixel values from the image which are thresholded to categorise them as "black", or "white", thus forming a two-tone image. Aggregates or averages of the "black" and "white" pixel values are used to derive the contrast measurement according to the formula: (Imax-Imin)/Imax where Imax is the average value of the "white" pixels and Imin the average value of the "black" pixels.
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