The four color photographs on the cover of this issue of The Atom were made from computer-generated color film. Of the two larger photographs, the top one represents a Sherwood plasma run. It was one of the Laboratory's earlier attempts in producing color and was done by presensitizing the background with blue light. The photograph at the bottom shows expanding gas in partially ionized air. The gas is represented by red particles and air by green particles. Contour lines for magnetic fields are in blue. The other colors are a result of mixing.
Of the two smaller photographs the top one shows a polar coordinate run of expanding gas made from film that had been presensitized with blue light. The other photograph represents the cross section of a nuclear reactor fuel element and shows the distribution of the three isotopes present.
On the back cover are black and white renditions of the two larger photographs. Notice the detail with which color shows mixing of elements when compared to their black and white counterparts, especially in the bottom photograph. In this frame, a field line instability (the erratic blue line in the red portion) was not known to exist until this color run was made.
Ever since the modern-day computer peered over the technological horizon, man has been hell-bent on getting it to do more faster. He endowed the computer with the capability of producing graphic information and in a short time computer-generated black and white film became commonplace. From here it was only natural to reach for color film production.
As a result, computer-generated color film is now in its infancy. The know-how necessary to produce it hasn't been so much a problem as the know-how to produce it economically enough so researchers can afford to use it. The big economic factor is time. On large industrial computers every minute is valued at several dollars.
A team of scientists at the Los Alamos Scientific Laboratory felt that in order for color-film production to be economically feasible, it should require no more computer time than an equivalent black and white run and should not sacrifice sharpness or clarity. With this in mind the scientists came up with a technique of generating color film that is currently being put to advantageous use at Los Alamos.
There are several advantages to using color in basic research, said Donald Dickman of C-A. First of all, color has a distinct impact that black and white doesn't have. Wherever our color film has been shown, the reaction has been startling and favorable. We can do things with it that we've never been able to do before. We can put more information on a single frame than is possible with black and white. The clarity with which we can show how different materials mix, for example, is impossible with black and white.
Los Alamos achievements in computer-generated color film followed a pioneer research program by Sandia Laboratories in cooperation with Stromberg-Datagraphics, Inc., in 1967. Sandia's approach and the method now being used at Los Alamos logically take-off from the black and white production methods. The information generated by the computer is on magnetic tape. The tape is fed into a Stromberg-Carlson SC4020 printer/plotter which converts the information into a graphic display on the face of a cathode ray tube where it is photographed. In appearance, the image on the cathode ray tube is much like the image seen on a black and white television set.
Between the cathode ray tube and the camera lens, the Sandia researchers placed a color filter wheel which was driven in one direction by a stepping motor. In each quadrant of the wheel was a filter; these were red, green, blue and clear. The idea was to photograph the image on the tube through a color filter with color sensitive film. However, the filters reduced the amount of light reaching the camera lens. This factor, coupled with film-speed limitations, made it impossible to obtain adequate exposure except by overstriking. This is a term meaning the computer repeats the information on the magnetic tape more than once. By having the computer overstrike from seven to nine times, the image was repeated a like number of times on the cathode ray tube. This allowed a longer period of time for the image to soak into the film emulsion.
This method produced satisfactory results but at the same time was convincing evidence that color film generation could be an expensive proposition. Overstriking on the computer and longer exposures on the printer/plotter took too much time for color-film generation by this method to be economically feasible. In addition, the time required to rotate and stop the color wheel further jeopardized the technique. Every quarter turn of the wheel required 200 milliseconds (one-fifth of a second). Use of the filter in the third quadrant then, required 600 milliseconds to move into position and stop.
In 1968, Los Alamos scientists became interested in color film production. They studied Sandia's method and other approaches, such as tinting which had been attempted at other computer installations. Interest, however, soon waned because of the necessity of overstriking to obtain the best results.
In the spring of 1969 we were approached by Dick Morse of P-18 about the possibility of color production for Sherwood and high altitude phenomenology, Dickman said. We said we would do it if we could find a way of doing it without overstriking.
A cooperative effort among Groups C-4, C-8 and ISD-7 began, aimed toward obtaining color film with a single computer strike. One of the first methods attempted was to presensitize film on the printer/plotter. This means the film was exposed to light through a color filter. Upon development, the film would have a background of the color to which it was exposed. David Buckner of C-8 had presensitized some film while conducting a study of various color filters. Dickman suggested that an image produced by a single computer strike might be seen against these backgrounds.
Presensitizing was tried with the colors green, red and blue. Blue showed the most promise but was still unsatisfactory. Bob Crook, ISD-7 group leader, and Frank Berry, also of ISD-7, experimented with extended-development of the film and produced better results.
Presensitizing film was still not the answer to economic generation of color film. By using one color to provide a background, only three were left to do the plotting. In addition, sweeping the background took an inordinate amount of time on the printer/plotter. The money saved by using only a single computer strike would be spent in presensitizing film on the printer/ plotter.
At the same time, Buckner was studying filter positioning devices. He built a color wheel whose filters could be positioned in 50 milliseconds. The device, however, required large amounts of electrical power and heating of associated electronics was a problem.
Buckner discarded the idea of using a wheel for positioning of the filters. Instead he built a device in which each filter was mounted on a magnesium arm. Each arm was driven by a solenoid and could position a filter in about 30 milliseconds (including 10 milliseconds during which the filter assembly oscillated after it was moved into position).
New filters were installed in the device to allow more light to pass through, the camera lens aperture was changed to admit more light (from f/5.6 to f/3.5) and was later replaced by a better-quality lens, a brighter-image cathode ray tube was procured, and extended development of the film was increased from a one-stop push to a two-stop push. These are development procedures designed to compensate for underexposure of film. A one-stop push essentially doubles the speed of the film and a two-stop push quadruples it.
Because of equipment limitations at the Laboratory, processing of computer-generated color film is being farmed out, and because of the necessity of having it processed in a restricted area, it is presently being sent to Kirtland Air Force Base in Albuquerque.
As a result of its efforts, LASL now offers its scientists computer-generated color film which takes no longer to produce on the computer than black and white, and increases printer/plotter time by a factor of only two and a half per cent. Color is being produced on 16-millimeter motion picture film and 35-millimeter still camera film.
Even this is not: the ultimate. Los Alamos scientists are currently experimenting with new techniques and instrumentation that show promise of trimming production time and costs even more. Buckner is working toward completion of a new device which will offer a selection of 10 color filters and will position any one of them within 14 milliseconds. A newly developed cathode ray tube is on order which will display images with greater resolution and with variable intensity. These improvements and the removal of a pellicle which cuts down on the light allowed to pass through to the camera lens are expected to eliminate the necessity of extended-development processing.
