Patent ID: 6826307
Filing Date: 2004-11-30
Classification: G06T

Abstract:
Apparatus for determining the contrast of a mark, said apparatus comprising:image sensor means (16) for capturing a two-dimensional image of at least part of said mark and a background, means (24) for sampling said captured image over a plurality of pixels in the mark and over a plurality of pixels in the background, to obtain respective intensity values for pixels in said mark and pixels in said background respectively, characterised by contrast determining means (24) for determining the contrast of said mark based on an aggregate or average of said intensity values for pixels in the mark, and an aggregate or average of said intensity values for pixels in the background, and outputting a contrast value result as a measurement of legibility, said contrast determining means (24) being operable to threshold the pixel intensity values from the image using associated black and white threshold values to categorize the pixels as â€œblackâ€  or â€œwhiteâ€  respectively, and to determine a contrast measurement obtained according to the following formula: (Imaxâˆ’Imin)/Imax where Imax is the aggregate or average intensity value of the â€œwhiteâ€  pixels and Imin is the aggregate or average intensity value of the â€œblackâ€  pixels.