Method for assessing and controlling the sensitometric characteristics of photographic products

A method for controlling a process for making a photographic film or paper product, comprising the steps of:

• determining for the process and the product a set of control variables, CV.sub.i to CV.sub.n, for each of which a change of a known magnitude will produce a corresponding change in the density response of the product in one or more of three primary colors to exposure over a range of exposure steps;
• removing a sample from a production batch of the product;
• measuring the density response in three primary colors to exposure of the sample over the range of exposure steps;
• determining for each density response the deviation of the sample from an aim response for that color for the product;
• transforming the deviations or responses or both into sensitometric quality indicator parameters representing color radial error R, average density error D and contrast mismatch error M, wherein R is determined from data points entered within a closed elliptical curve in a color density balance plane with trilinear coordinates;
• transforming the aim response for at least one primary color into tolerance limit values for the quality indicator parameters, thereby defining boundaries of acceptable sensitometric quality of the product;
• determining a root mean square error HT of the density responses in accordance with the following expression:
• HT.sup.2 ={[.SIGMA..sub.i (r/L).sub.i.sup.2 ]/AXG.sup.2 +[.SIGMA..sub.i (g/L).sub.i.sup.2 ]/AXG.sup.2 +[.SIGMA..sub.i (b/L).sub.i.sup.2 ]/AXB.sup.2 }/3.SIGMA..sub.i (1/L.sub.i).sup.2,
• where .SIGMA..sub.i is the summation over the relevant step range;
• r.sub.i, g.sub.i and b.sub.i are density errors on exposure step i;
• L.sub.i is the tolerance limit value of the ith step;
• AXG is the length in density units of the green axis of the closed elliptical curve;
• and AXB is the length in density units of the semi-major blue axis of the closed elliptical curve;
• determining a root mean square DT of exposure stepwise values of D within a predetermined exposure step range, in accordance with the following expression:
• DT=[.SIGMA..sub.i (D.sub.i /L.sub.i).sup.2 /.SIGMA..sub.i (1/L.sub.i).sup.2 ].sup.1/2
• where D.sub.i is the value of D at the ith step;
• determining a root mean square RT of exposure stepwise values of R within a predetermined exposure step range, in accordance with the following expression:
• RT=[.SIGMA..sub.i (R.sub.i /L.sub.i).sup.2 /.SIGMA..sub.i (1/L.sub.i).sup.2 ].sup.1/2
• where R.sub.i is the value of R at the ith step;
• determining a weighted contrast mismatch MT, in accordance with the following expression:
• MT.sup.2 ={.SIGMA..sub.i [CM.sub.i /L.sub.i *].sup.2 }/.SIGMA..sub.i [1/L.sub.i *].sup.2,
• where CM.sub.i is the contrast mismatch for the ith contrast step interval;
• and L.sub.i * is the tolerance limit value in the center of the contrast step interval beginning with the ith exposure step;
• determining a square root CT of the sum of the squares of total contrast errors over all colors, in accordance with the following expression:
• CT.sup.2 =WTCE.sub.R.sup.2 +WTCE.sub.G.sup.2 +(AXG/AXB).sup.2 (WTCE.sub.B.sup.2),
• where each WTCE is determined in accordance with the following expression:
• WTCE.sup.2 ={.SIGMA..sub.i [CE.sub.i /L.sub.i *].sup.2 }/.SIGMA..sub.i [1/L.sub.i *].sup.2,
• where CE is the average contrast error for each color in percent over an n-step interval beginning with the ith step;
• defining a quality objective function F, in accordance with the following expression:
• F=f.sub.1 [HT/w.sub.1 ].sup.2 +f.sub.2 [DT/w.sub.2 ].sup.2 +f.sub.3 [RT/w.sub.3 ].sup.2 +f.sub.4 [MT/w.sub.4 ].sup.2 +f.sub.5 [CT/w.sub.5 ].sup.2,
• where f.sub.1 to f.sub.5 are weighting factors and w.sub.1 to w.sub.5 are normalizing factors;
• using the changes to the set of control variables and the corresponding changes to the density responses to determine the magnitudes of the control variables for minimization of the value of the quality objective function;
• and
• adjusting the magnitudes of the control variables to achieve the minimization and control the said process for making a photographic film or paper product.