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: (I.sub.max -I.sub.min)/I.sub.max where I.sub.max is the average value of the "white" pixels and I.sub.min the average value of the "black" pixels.
Electronically programmed signs consist of any array of picture elements (pixels) that can be controlled independently to create an image. Varying the intensity of each pixel and adding multiple colors per pixel will enhance the image quality. It is currently common to have displays that use one, two or three separate colors in a pixel (monochrome, red-green, and red, green and blue) with intensity levels of two, four, eight up to 256 and beyond. Multiple colored pixels can combine colors at various intensity levels to expand the displayable color palette. The number of colors it is possible to display is calculated by the following formula:.times..times..times..times..times..times..times..times..times..t- imes..times..times..times..times..times..times..times..times..times..times- ..times..times. ##EQU00001## While raising the number of intensity levels and colors improves image quality, it also raises the viewer's sensitivity to inconsistencies in both parameters.
