Apparatus for measuring opaque medium coverage of a translucent sheet

A method of determining the area of opaque medium coverage of a sheet of translucent material of undetermined size comprising:

• (a) providing a relatively large size-calibration sheet which is constructed of material having substantially identical light transmitting properties to that of the sheet of material for which opaque medium coverage is to be determined, said size-calibration sheet having substantially no opaque medium thereon;
• (b) providing a plurality of coverage-calibration sheets having different, known degrees of opacity;
• (c) mounting said size-calibration sheet on a light table;
• (d) selecting a number of differently-sized areas to be used as area-calibration values;
• (e) blocking off light transmission from portions of said light table other than a portion thereof which is covered by said size-calibration sheet and which is equal to one of said selected differently-sized areas of step (d);
• (f) light sealingly covering the sheet mounted on the light table with an internally light diffusive enclosure;
• (g) measuring the intensity of diffused light within the enclosure;
• (h) repeating steps (e) through (g) for each of said selected differently-sized areas;
• (i) using the known area of each selected differently-sized areas and the associated measured light intensity value for each area, constructing a size-calibration graph with measured sheet area as one coordinate axis and measured light intensity as the other coordinate axis;
• (j) mounting the sheet of material for which opaque medium coverage is to be measured on the light box;
• (k) blocking off light transmission from portions of said light table other than the portion thereof which is covered by said sheet of material for which opaque medium coverage is to be measured;
• (l) light sealingly covering the sheet mounted on the light table with the internally light diffusive enclosure;
• (m) measuring the intensity of diffused light within the enclosure;
• (n) recording the light intensity measurement thus obtained;
• (o) mounting the size-calibration sheet on the light table;
• (p) blocking off a portion of said size-calibration sheet which is identical to the configuration of the sheet of material for which opaque medium coverage is to be determined;
• (q) light sealingly covering the sheet mounted on the light table with an internally light diffusive enclosure;
• (r) measuring the intensity of diffused light within the enclosure;
• (s) recording the light intensity measurement thus obtained;
• (t) mounting one of said coverage-calibration sheets on the light table;
• (u) blocking off a portion of said coverage-calibration sheet which is identical to the configuration of the sheet of material for which opaque medium coverage is to be determined;
• (v) light sealingly covering the sheet mounted on the light table with an internally light diffusive enclosure;
• (w) measuring the intensity of diffused light within the enclosure;
• (x) repeating steps (t) through (w) for each of said coverage-calibration sheets;
• (y) using the known degree of opacity for each coverage-calibration sheet and the measured light intensity value for each sheet, constructing an opaque coverage-calibration graph with degree of opacity as one coordinate and measured light intensity as the other coordinate;
• (z) comparing the light intensity measurement recorded in step (n) to the opaque coverage-calibration graph to determine the relative coverage of said sheet of material with opaque medium;
• (aa) comparing the light intensity measurement of step (s) to the size-calibration graph to determine the area of said sheet of material;
• (bb) computing the area of opaque medium coverage of said sheet from the determined relative coverage of step (z) and the determined sheet area of step (aa).