# Predicting color print filtration and exposure

## Abstract

A method of mathematically modeling the response of a system in which color reflection prints are made from a negative was investigated. Data was generated by making a series of prints with different yellow and magenta filtrations at a series of exposures. First, second and third order regression curves were fit to the filtration versus reflection density curves and the exposure versus density curves that were thus generated. The predictions of the sets of equations were compared to the data and it was found that the filtration could be predicted more accurately than the exposure time, because, the response curves of the system change in shape when the exposure is varied. The third order equations were found to be much more complicated to use than the second order equations but were not significantly more accurate in making predictions. The second order equations were able to predict a filtration and exposure that would produce ii print densities a total of 0.25 density units from the specified aim densities. A print made using the predictions of the second order model on the same print paper, and using the same enlarger and precesser as the original data was generated on was made, and the resulting densities were .216 units from the aim density. A print made using a different print paper and enlarger showed that a method of changing the model was needed in order to make accurate predictions under varied conditions. Two computer programs were devised, for this purpose. The simplest uses the assumption that the shapes of the filtration and exposure versus density curves always stay the same, and simply shift backwards and forwards or up and down, as the exposure changes, or the enlarger, print paper or processer is changed. The second program is to be used when this assumption fails and uses regression techniques to fit new second order equations to the data that the user is required to generate. A print made using the first of these two programs has densities that are a total of .287 density units from the aim density. A print that is .287 density units from ideal is acceptable to very few people. More work needs to be done in order to improve the accuracy of the system if it is to be a practical tool in the making of color prints.

## Library of Congress Subject Headings

Color photography--Printing processes

4-1-1981

Thesis

## Department, Program, or Center

School of Photographic Arts and Sciences (CIAS)

Carson, J.F.