Method of and apparatus for identifying presensitized offset printing plates

An apparatus for identifying a presensitized offset printing plate with a photosensitive layer thereon comprising

• (a) a tray for receiving the presensitized plate to be tested;
• (b) a measuring head having a white light emitting source and four detecting means for detecting the respective intensity levels of the light reflected by the photosensitive layer in each of four color bands for deriving a black-and-white signal, cyan signal, magneta signal and yellow signal, said measuring head moving relative to the presensitized plate such that said individual intensity levels of the reflected light in said four color bands are detected from a plurality of spots along a scanned path on the photosensitive layer;
• (c) computing means having calculating means, comparing means and data memory means, said calculating means calculating mean values as well as variance values with respect to said four colors from said intensity levels measured from the respective spots along the scanned path so as to present test data characteristic of the plate under, said data memory means storing a plurality of sets of reference data, each set of said reference data is composed of the intrinsic mean values and variance values which have been obtained with respect to said four colors for each of a plurality of known plates of different light reflective characteristics, and said calculating means incorporates for incorporating said test data into each of a plurality of sets of reference data to form corresponding numbers of groups, and calculating correlation ratios with respect to said four colors for each group so as to get the sum of the correlation ratios therefor, and said comparing means for comparing the sum of the correlation ratios among said groups to fing the group having a minimum value of said sum such that the test data may be determined to be substantially identical to the particular reference data which forms with the test data said group having the minimum value whereby the plate under test is identified as one of the reference plates;
• (d) data input means for storing the reference data intrinsic to a known presensitized plate in said data memory means, said data input means having first and second data input functions, such that in said first data input function the reference data are inputted to the data memory means in the form of numerals and in said second data input function the reference data are inputted to the data memory means by the use of said measuring operation of said measuring head;
• (e) name input means for designating the reference data entered in the data memory means;
• and
• (f) an output device for indicating the content of the reference data obtained by said computing means as well as the names designated with said name input means.