LogEtronic simplification in simulated color radiography.

Abstract

The recent introduction of the LogEtronic Contact Printer has provided a means of ready simplification in the preparation of simulated color roentgenograms. As indicated in our initial report on simulated color roentgenography (1), it is necessary first to obtain a black and white negative of the roentgenogram selected for color reproduction. From this negative an exposure is made by contact or enlargement, usually the latter, onto Matrix or Pan-Matrix film. The exposed film is then processed, by the steps specified in Table I, to produce a gelatin relief image for the addition of the Flexichrome colors as desired. The quality of the original negative is one of the most important single factors in the success of the final color preparation. A good original negative must contain and transmit all of the definition desired for proper form and value in the final result. This result is a color roentgenogram that realistically represents the selected roentgenogram as naturally as possible. The routine visual adaptation procedures in the darkroom usually cause an accentuation of shadows visible to the eye at the exposure of the photographic negative. Consequently, an unequal or uneven distribution of light over the preparation is much more apparent in the reproduction than in the original. To eliminate and counteract these deficiencies, the preparation is usually carefully lighted to lower subject contrast than required in the final reproduction. The great difficulty is to keep even lighting over the entire preparation. The necessity for this low-contrast lighting is accentuated by variable areas of contrast in the original roentgenogram. The important point is not to permit areas to become too dark to show detail and yet not too accentuated to bring about artificiality (2). One solution to this problem is the new method of LogEtronic photographic printing, which reproduces accurately at midscale the most useful portions of the density range of the negative. The LogEtronic process utilizes the device of “dodging.” It involves a completely automatic one-step, one-material operation as outlined in the Instruction Manual (3). As one becomes familiar with the use of the printer, he will be able to produce high-quality negatives with a constancy which is desirable for routine purposes. In an excellent article St. John and Craig have described the basic principle of the LogEtronic Contact Printer and have outlined in detail its operation (4). They illustrate the improved photographic effect obtained by “dodging” in simultaneously increasing and decreasing contrast. In an ordinary print highlight and shadowy regions are printed at opposite extremes of the density scale, and detail merges with the background. The LogEtronic process “dodges” these two regions and approximates them to average density; gross contrast is reduced, while detail contrast is increased, resulting in better reproduction and improved visualization (Fig. 1).