A Study to Eliminate Moire Patterns Produced in Color Separations When Scanning Polachrome CS Transparency Film on the Hell DC-300 B/L Laser Scanner

The Polaroid Corporation, in May of 1983, introduced Polachrome CS color transparency film and a new process called the Autoprocess system. This system offers the convenience of obtaining instant color transparencies in about three minutes. The film has excellent projection and viewing characteristics. The product was designed to have its largest market with professional photographers. Polachrome\u27s construction creates problems for the printer in that moire patterns occur during the separation process. This study gives a short background for both additive color screen films and dye layer films, and a comparison is made to help the reader understand the problems with scanning Polachrome film. When attempting to scan Polachorme CS film, moire patterns are produced because of the color filters which make up the film. The emphasis of this study was to determine which scanner controls could be used to remove the moire patterns. Polachrome CS film is based on the principle of an additive color screen theory. The film contains many layers, one layer consisting of red, green, and blue filters which either passes or stops light. When this filter layer is viewed by the scanning lens an interference pattern called moire is produced by the variables of screen ruling, unsharp masking controls, and the angle of the transparency on the scanning drum. The hypothesis states that Polachrome CS color transparency film can be scanned on the DC-300 B/L laser scanner, so that separations are free of all moire patterns with acceptable definition. Pre-testing was necessary to determine which variables of the scanning process had an effect on producing a moire pattern. The results of the pre-tests determined the final choice of variables, which were then tested together. Defocusing, unsharp masking (intensity and starting point), as well as the angle at which the transparency is mounted, were determined to be the major variables that cause a moire pattern when scanning Polachrome CS transparency film. From the combination of these variables a total of 48 proofs were generated for the visual experiment. The visual experiment had two parts, involving 30 viewers, viewing the 48 proofs. Part I dealt with a question relating to moire patterns and Part II dealt with a question relating to the definition of the image. Data was recorded and analyzed. The hypothesis, that separations can be generated free of moire patterns with acceptable definition, was proven by 16 percent of the proofs tested. This resulted in a set of recommendations given as guidelines to follow when Polachrome transparency film is electronically scanned on the DC-300 B/L laser scanner