Print scanner

A method of examining printed labels of opaque compact discs having reflective surfaces, which discs have been moved through a printing station by a conveyor including the steps of providing a camera station at a predetermined position along said conveyor, exposing an acceptable reference label to a scanning video camera at said camera station to acquire an image made up of a plurality of pixels of said reference label, storing said reference label image, stationarily positioning a plurality of successive discs to be tested within said camera station, exposing a disc stationarily positioned in said camera station to light to acquire a test image made up of a multiplicity of pixels of the label of said disc and subtracting one of said images pixel-by-pixel from the other image to obtain a measure of the acceptability of a label being tested, said test image acquiring step comprising averaging a plurality of test label images.

A method of detecting defects in the printed label of a compact disc including the steps of positioning a disc having a reference label in operative relationship with a scanning camera, averaging a multiplicity of reference label frames from said camera and storing the resultant reference image, positioning a sample disc in operative relationship with said scanning camera, averaging a plurality of sample label frames to provide a sample image, subtracting said reference image pixel-by-pixel from said sample image, computing a histogram of the subtracted result, calculating a figure of merit for missing ink from said histogram averaging a plurality of sample label frames to provide another sample label image, subtracting said other sample image pixel-by-pixel from said reference image, computing a second histogram of the result of said second subtracting step calculating a figure of merit for added ink from said second histogram and accepting or rejecting said sample disc on the basis of said figures of merit.

Apparatus for scanning a printed area to determine the existence of defects therein including in combination means for acquiring and storing an image made up of a multiplicity of pixels of an acceptable area, means for acquiring an image comprising of a multiplicity of pixels of a test area, means for subtracting one of said images pixel-by-pixel form the other image, means responsive to said subtracting means for computing a histogram of the subtracted results and means for calculating a figure of merit on the basis of said histogram, said calculating means comprising means for dividing the gray level sum of all pixels produced by said subtracting means by the zeroth element of the histogram.

Apparatus for detecting defects in the label area of a compact disc having a central opening and a non-printed area adjacent to said opening and supported by a carrier advanced intermittently along a predetermined path through a printing station including in combination, a substantially light-tight housing disposed at a point along said path beyond said printing station, an inlet port for admitting carriers into said housing, an outlet port through which carriers can emerge from said housing, means within said housing for illuminating the label area of a sample disc with diffuse light, a video camera within said housing for acquiring an image of an illuminated label area and means responsive to the output of said camera for producing an indication of a label defect, said illuminating means comprising a mask for blocking light from all of said disc except said label area.