For the past 12 months, the graphics group at Logic Data Systems has devoted a considerable amount of time to improving and expanding existing techniques in the production of computer animation at LDS. These efforts have been primarily in three areas:
Two inch video tape is used a great deal as a production medium in the Dallas area, and for this reason we undertook to find out something about the process in order to see what possibilities video tape techniques might have for computer animation.
Through the cooperation of WFAA-TV in Dallas, we found that electronic video processing of a television image, involving video tape recorders and the new video disc recorders, can perform many of the functions of an optical printer such as matting, adding color to black and white images, and production of multiple pass effects, as well as some special effects that can't be readily produced with an optical printer.
Of course, the end product is on video tape. If the production is to be used for television, this is fine. However, if the material is to be delivered on 16mm film, the tape-to-film transfer is a relatively expensive process at the present time. In addition, the tape-to-film methods that we have examined involve the photographing of a television monitor with the inherent limitations of the 525 line television raster to resolution, regardless of the quality of the computer generated original.
There are methods for eliminating the horizontal scanning lines in the television raster, or making them less apparent in some cases, during the tape-to-film process although of course, this does not improve the resolution. We felt that for some applications, some of the better tape-to-film methods would probably be acceptable for 16mm film, provided the cost was not unreasonable.
Production of computer animation for video tape involves generation of black and white 16mm film, using a DatagraphiX 4060 or an FR-80, with color separations if required, just as we would do when using an optical printer. The black and white material is then transferred to two inch video tape, using the film chain at the television studio.
At this point, we have a black and white A roll or video key source on video tape that can be used in several ways. The animated figures on the key can be supered over another image - either live action or animation - from a video tape, film, or television camera source. The images can be colorized as they are supered, with the colors being generated electronically in some studios, or in some cases generated by training a color television camera on a color card to provide a source.
Through the video keying or matting process, the moving black and white image on the A roll acts as a window through which we see the color field, thereby producing a new tape with the moving image in color.
In combining images from the video tape A roll and another source, the black and white A roll acts as a control or key which causes the video signal from the color source to be output from the controller for recording when the equipment is scanning the clear portions of each frame on the A roll. When scanning the black portions of each frame on the A roll, the signal from the alternate source is output from the controller for recording. This electronic matting process is generally referred to as a video overlay, since the image from the A roll appears to be in front of, or on top of, the image from the alternate source.
A similar method involves keying from a portion of a video signal of a particular color and inserting an alternate signal. We have used this method to combine live action and computer animation by shooting the actors in front of a blue background while keying from the blue background to insert the animation. The actors could see the composite image on the studio monitor during the taping. This process is called a video inlay, and in the resulting image, the animation appears to be behind the actors, in place of the blue background.
A number of special effects are possible with video tape equipment. One we have used a great deal involves video feedback, obtained by training a television camera on a studio monitor displaying the computer animation, and taping the result. This produces multiple images or repeats in the composite signal, and by varying the orientation of the camera and the monitor, a great variety of fascinating effects are possible.
These electronic matting processes I have described are used a great deal in larger television studios for supering still art (titles, logos, etc.) over live action material for locally produced television spots, as well as for inlaying 35mm slides - behind a TV news commentator, for instance. However, the use of computer animated film makes possible an economical animated source as a key, and this addition of motion is leading to a fascinating new tool for television production.
A new piece of equipment with which we have done some limited experimentation is a video disc recorder. The disc recorder can store up to 30 seconds of color video, and can be programmed to replay any part of this stored information in fast or slow motion, or to cycle selected frames.
In the demo films I have with me, you will see several black and white segments that were used for television productions. I have available a two inch video tape illustrating the end product after video processing. Copies of the two inch tape are also available on one inch video tape for an IVC recorder format.
The technique of shading or blocking figures has been a useful one. We have used this addition to our IMAGE animation program in almost every job we have delivered since its implementation early this year. The method involves plotting of multiple parallel lines within the boundary of the figure to be shaded. Refinements in ordering of the boundary segments for intersection tests, and methods for limiting the search radius for intersection tests in the shading subroutine have made the process an economical one in terms of computer time.
We have encountered some problems in producing film containing shaded data arrays on the DatagraphiX 4060 and FR-80 plotters from time to time. In two cases when using DatagraphiX 4060's, we have encountered a variation in intensity from vector to vector in a particular figure. This seemed to be related to the lengths of the shading vectors being plotted, and may have been a problem in adjusting the machines.
For the DatagraphiX 4060, we have found that a spacing of five raster coordinates between adjacent shading lines produces a uniformly shaded field without burning or haloing of the image. A limited spacing between shading lines is preferable to an overlap, since haloing is very noticeable, whereas small spaces between shading lines will not be discernable on a 16mm reduction. Uniform spacing and intensity are very important, particularly when producing color separations for an end result on color film.
The six black and white WFAA Production logos you will see in the demo film were produced on an FR-80, and point up a problem we have had occasionally in using this equipment - that is, sometimes the spot diameter or intensity varies over a short period of time. The six variations of the WFAA logo you will see are shown in the order they were plotted on an FR-80, in one run of about 20 minutes duration. The spacing between shading lines is set at 26 raster coordinates in each of the 6 segments and yet the variations in intensity of some of the segments is very noticeable. Since the end product here was to be on video tape, it was possible to adjust the sensitivity to eliminate the halo around the image after the film-to-tape transfer. This problem may be limited to the particular FR-80 we have been using.
I have some CalComp plots obtained during checkout of our CHAP I program (Character Animation Program, version I). This program was developed as a test for an idea relating to character animation - that is, programming character action by selecting key positions from the master list of positions possible, with related timing and scaling information. We believe this approach has merit for several reasons: