Method of photographic reproduction and apparatus therefor

Claim 1

PHOTOGRAPHIC REPRODUCTION APPARATUS COMPRISING A SCANNING SYSTEM FOR GENERATING A BEAM OF LIGHT AND SCANNING IT OVER A TRANSPARENT IMAGE TO BE REPRODUCED AND A LIGHT SENSITIVE COPYING MATERIAL TO PROVIDE AN IMAGE OF THE FORMER ON THE LATTER, A FIRST LIGHT SENSITIVE DEVICE RESPONSIVE TO THE LIGHT FROM SAID SCANNING BEAM WHICH IS REDUCED BY THE TRANSMISSION OF THE INDIVIDUAL POINTS OF SAID TRANSPARENT IMAGE AS SAID BEAM SCANS THEREOVER, A SECOND LIGHT SENSITIVE DEVICE RESPONSIVE TO THE INTENSITY OF SAID LIGHT BEAM, FIRST AND SECOND LOGARITHMIC AMPLIFIERS IN SERIES WITH SAID FIRST AND SECOND LIGHT SENSITIVE DEVICES RESPECTIVELY, FIRST AND SECOND SIGNALS APPEARING ON THE OUTPUT OF SAID FIRST AND SECOND LOGARITHMIC AMPLIFIERS, SUBTRACTING MEANS ADAPTED TO SUBTRACT SAID FIRST SIGNAL FROM SAID SECOND SIGNAL TO PROVIDE A THIRD SIGNAL WHICH IS DEPENDENT ON THE DINSITY VALUE OF EACH INDIVIDUAL POINT SCANNED, A TONE CORRECTION COMPUTER FOR MODIFYING SAID THIRD SIGNAL IN ACCORDANCE WITH THE DENSITY VALUES REQUIRED IN THE COPYING MATERIAL, A COMPARISON DEVICE RESPONSIVE TO THE MODIFIED THIRD SIGNAL AND SAID FIRST SIGNAL TO PROVIDE A SIGNAL FOR CONTROLLING THE SCANNING BEAM SO AS TO MAINTAIN THE DIFFERENCE BETWEEN THE MODIFIED THIRD SIGNAL AND SAID FIRST SIGNAL SUBSTANTIALLY TO ZERO.