
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. ...











