Exposure control system for color printers

Claim 1

AN EXPOSURE CONTROL SYSTEM FOR A PHOTOGRAPHIC COLOR PRINTER OF THE TYPE HAVING A PLURALITY OF INDIVIDUALLY CONTROLLABLE PRINTING LIGHT SOURCES EACH OF A DIFFERENT COLOR, AND MEANS FOR DIRECTING LIGHT FROM SAID SOURCES THROUGH A NEGATIVE TO BE PRINTED AND TOWARD A PRINTING STATION, SAID SYSTEM COMPRISING A MULTI-CHANNEL EXPOSURE COMPUTER, ONE CHANNEL CORRESPONDING TO EACH OF SAID COLORS, AND EACH CHANNEL COMPRISING DENSITOMETER MEANS CONTROLLED BY AND RESPONSIVE TO LIGHT OF THE ASSOCIATED COLOR PASSING THROUGH SAID NEGATIVE FOR PRODUCING AN OUTPUT SIGNAL CORRESPONDING TO THE AVERAGE COLOR DENSITY OF THE NEGATIVE FOR THAT PARTICULAR COLOR, STORAGE MEANS FOR STORING SAID COLOR DENSITY SIGNAL, A SIGNAL MIXER CONJOINTLY RESPONSIVE TO THE COLOR DENSITY SIGNAL STORED IN SAID STORING MEANS FOR THAT PARTICULAR CHANNEL AND THOSE COLOR DENSITY SIGNALS STORED IN THE STORAGE MEANS FOR THE OTHER CHANNELS TO PRODUCE AT ITS OUTPUT A VOLTAGE HAVING A PREDETERMINED RELATIONSHIP TO, AND INDICATIVE OF, THE DESIRED LOG EXPOSURE FOR THAT PARTICULAR COLOR; PROGRAMMING MEANS FOR CONJOINTLY RENDERING SAID LIGHT SOURCES OPERATIVE TO INITIATE AN EXPOSURE CYCLE, A LOG TIMER COMMON TO ALL SAID CHANNELS AND RESPONSIVE TO SUCH ACTUATION OF SAID PROGRAMMING MEANS FOR PRODUCING AN OUTPUT VOLTAGE WHICH VARIES FROM A PREDETERMINED INITIAL VALUE AS THE LOGARITHM OF THE ELAPSED TIME FROM THE INITIATION OF SAID EXPOSURE, AND CONTROL