Exposure control method for an automatic color printer with slope control

Claim 1

A method of controlling the exposure time in an automatic color printer for obtaining color prints from color negatives in accordance with a control formula, log 10 T=f(D), where T is the controlled exposure time and D is the large area transmission density of the color negative, wherein the conditions of log.sub.10 (K.sub.6 /K.sub.4)K.sub.2 log.sub.10 K.sub.3 K.sub.I I.sub.o =0, and K.sub.5 =K.sub.2 =-1 are satisfied, in which K 1 , K 2 , K 3 , K 4 , K 5 , and K 6 are preselected constants and I o is the amount of light incident to the color negative, in which a slope control is performed, the method comprising the steps of: measuring the amount of light transmitting through the color negative and generating an output indicative of the transmission density of the negative represented by K I I o ·10 -D ; log converting the output based on a conversion function of y=K 2 log 10 K 3 x, where y is the output of L 1 of the log conversion and x is the input thereof, corresponding to said output K I I o 10 -D indicative of the transmission density; converting the log converted output to a slope control value based on a conversion function represented by L 2 =f(L 1 ), where L 2 is the slope control value and L I is the output of the log conversion; exponentially converting the slope control value L 2 based on a conventional function of y=K 4 10 K 5.sup.·x where y is the output of the exponential conversion and x is the input thereof corresponding to said input L 2 , and K 6 is said preselected constant; integrating the exponentially converted slope control value; comparing the integrated value with a preselected constant; and determining the exposure time of the color printer, when said integrated value has become equal to the preselected constant.

Claim 2

A method of controlling the exposure time in an automatic color printer for obtaining color prints from color negatives in accordance with a control formula, log 10 T=f(D), where T is the controlled exposure time and D is the large area transmission density of the color negative, wherein the conditions of log.sub.10 (K.sub.6 /K.sub.4)K.sub.2 log.sub.10 K.sub.3 K.sub.I I.sub.o =0, and K.sub.5 =K.sub.2 =-1 are satisfied, in which K 1 , K 2 , K 3 , K 4 , K 5 , and K 6 are preselected constants and I o is the amount of light incident to the color negative, in which a slope control is performed, the method comprising the steps of: measuring the amount of light transmitting through the color negative and generating an output indicative of the transmission density of the negative represented by K I I o ·10 -D ; log converting the output based on a conversion function of y=K 2 log 10 K 3 x, where y is the output of L 1 of the log conversion and x is the input thereof, corresponding to said output K I I o 10 -D indicative of the transmission density; converting the log converted output to a slope control value based on a conversion function represented by L 2 =f(L 1 ), where L 2 is the slope control value and L I is the output of the log conversion; exponentially converting the slope control value L 2 based on a conventional function of y=K 4 10 K 5.sup.·x where y is the output of the exponential conversion and x is the input thereof corresponding to said input L 2 , and K 6 is said preselected constant; integrating the exponentially converted slope control value; comparing the integrated value with a preselected constant; and determining the exposure time of the color printer, when said integrated value has become equal to the preselected constant.