The Effect of flashing in reducing the tonal range of a transparency for photomechanical reproduction

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Title: The Effect of flashing in reducing the tonal range of a transparency for photomechanical reproduction
Author: Al-Hajji, Bader N.
Abstract: Photographic processing and lithographic printing reproduction are two different processes. In photography, the transparency reproduces the original scene in continuous tone. Whereas, in lithographic printing, the reproduction is a result of an all-or-nothing process. A transparency may have a tonal range that exceeds the range that can be reproduced in lithographic printing. So tone compression is performed on transparencies that exceed the tonal range for printing. Avoiding tone compression during lithographic production results in considerable savings in cost and time. One of the methods to reduce tonal range is for the photographer to understand the relationship between emulsion flashing and the tonal range of transparencies. Flashing is the process of projecting nonimage white light to the film emulsion either before or after exposure, but prior to processing. This study investigated the relationship between flashing and exposure for a transparency which would reduce its tonal range and make it suitable for printing. The hypotheses under investigation were: (1) it is possible to flash Ektachrome transparency film by a predetermined amount of light to produce a desired reduction in the tonal range of a transparency, making it more acceptable to the printing range of lithographic printing when using coated paper; (2) the post-flashing technique produces the most acceptable result in achieving the desired tonal range as compared to the pre-flashing technique; (3) the flashing technique produces the same result in a transparency as the image prepared by the use of adjusting the lighting ratio in measured photography. An experimental investigation was conducted. A setup consisting of standard scales was photographed at various exposures and different degrees of flashing. The photography was performed using a 4X5 camera. The setup was illuminated at 45 angles by means of two strobe lights. Exposure was controlled by altering the aperture opening of the lens or fstop. The degree of flashing was determined by pre-exposing or post-exposing the Ektachrome transparency film emulsion to non-image white light through sheets of parchment paper placed at a distance of three inches from the camera lens. The amount of light that could reach the lens during flashing was controlled by varying the number of sheets of parchment paper. Thirty-two transparencies were photographed. The transparencies were processed by E-6 process. The tonal ranges of the transparencies were measured by means of a transmission densitometer. A visual test was conducted to determine the visual appeal of the transparencies by professionals in the field of photography and printing. The outcome of the experimental investigation showed that the tonal range of a transparency is reduced when the film emulsion is flashed. The results suggest that preflashing by an amount of a little over one-third of the light required for normal exposure and then exposing the film to the subject or setup at one and a half stop below the normal exposure produces transparencies that have a tonal range within the limits of lithographic printing and that are visually appealing. It was also shown that pre-flashing the film had a greater effect on reducing the tonal range than post-flashing. Moreover, the flashing technique was compared with methods used to reduce the tonal range by adjusting the lighting ratio. Based on these results, the first hypothesis was confirmed, the second was rejected, and the third was qualitatively accepted
Record URI: http://hdl.handle.net/1850/11266
Date: 1993-04

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