Optics: motion pictures – Methods – Recording
Reexamination Certificate
1997-07-28
2001-04-03
Morris, Terrel (Department: 1771)
Optics: motion pictures
Methods
Recording
C352S049000, C352S089000, C352S046000, C352S047000, C442S130000
Reexamination Certificate
active
06211941
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to composite photography, and more particularly to a matte process employing backing screens having improved chromatic actinic stimulus for color difference composite photography, cinematography, videography and solid state digital imaging.
2. Art Background
In motion picture production, it is often impractical, impossible or simply uneconomical to place actors in the specific environments to be depicted. To resolve this problem, various techniques have evolved over the years to composite such scenes from separately filmed “elements.” The patent literature contains a great deal of teaching in this field. A comprehensive discussion is to be found in my prior patents. See U.S. Pat. Nos. 4,417,791, 4,548,470 and especially 4,629,298. Reference is also made to the
American Cinematographer Manual, Seventh Edition
(hereinafter “the ASC Manual”), pp. 430-466, with particular emphasis on the section titled “Screen Types and Lighting” pp. 434-437. With these references in mind, the present discussion will be confined to a summary of the evolution of traveling matte technique.
The earliest efforts at composite photography generally resorted to animation, as in Georges Méliès' “Trip to the Moon” (1902). Thereafter, techniques such as the “held/take” process were utilized, in which a scene was shot with predetermined areas of the successive frames blocked off with an opaque “matte” in order to preclude exposure thereof. The unexposed portions of the successive frames were thereafter exposed to the desired foreground subjects, with the background areas “matted” to protect the previously recorded latent images. Essentially the same process is used to incorporate a painting which depicts a distant, dangerous, or totally alien scene against which the actors are to appear; this is known as matte painting. In order to depict actors or other foreground subjects moving in front of the desired background scenes, it became necessary to produce “mattes” that would change from frame to frame, or “travel.” Various techniques were developed over the years to accomplish this.
Early processes relied upon contrast alone, the foreground action being filmed against a jet black backing and the resulting image being printed through several generations of high contrast film stock or alternatively, having the image chemically “intensified” until a matte was produced. One example of this technique is described in U.S. Pat. No. 1,273,435 to Frank Williams in 1918.
The results obtained by this technique were generally quite poor, due to the inevitable distortion produced by the multiple reversals or the intensification which result in “haloes” or “fringes” occurring between the scene elements. Efforts to address these problems led to the exploitation of the chromatic response of black and white photographic film and resulted in the Dunning-Pomeroy process (U.S. Pat. No. 1,613,163 to Carrol D. Dunning, 1927) and another Williams process (U.S. Pat. No. 2,024,081, Dec. 10, 1935). With the advent of color film recording, notably the Technicolor process, the chromatic based systems began to proliferate. (See U.S. Pat. Nos. 2,693,126, and 2,740,712 to W. E. Pohl.).
The fundamental concept that makes it possible to derive a matte from a polychromatic photographic image is based on the fact that the superimposition of positive and negative images will cancel each other out and yield an opaque image. Thus it follows that if a given portion of the image is comprised of a pure monochromatic object, e.g., blue, this portion will appear as light in a print of the film record that is sensitive to blue and dark in prints of the film records that are not sensitive to blue, i.e. the red and green records. Therefore, if the red negative record, in which the “blue” object appears light, is superimposed with the blue positive record, in which the blue object also appears light, the blue object will remain the only significant “light” object in the scene, all polychromatic portions of the scene having canceled each other out to yield an opaque image. It is then straightforward to produce a set of positive and negative high contrast “mattes” and employ these to print, in succession, the foreground and background elements of a composite scene.
With the advent of monopak color photographic film it became possible to devise the ever more sophisticated color difference traveling matte techniques exemplified by Petro Vlahos' U.S. Pat. No. 3,158,477. As the compositing technology evolved to produce more convincing results, the requirements for the original photography of the “bluescreen” element became increasingly severe. Much ingenious attention was focussed on this area, and some of the results achieved have been recognized with patents and Academy of Motion Picture Arts and Sciences Scientific and Engineering Awards. Among these are: Eastman Kodak for color negative EC 5295, a film designed expressly for Bluescreen traveling matte photography (1987), the Stewart Traveling Matte Transmission Bluescreen backing (1964), the Blue-Max Blue Flux Front Projector (1984) (U.S. Pat. No. 4,629,298) and the Reverse Bluescreen Process (1983) (U.S. Pat. No. 4,417,791). The ultimate sophistication in traveling matte image acquisition is achieved with the Reverse Front Projection process described in the
American Cinematographer Manual,
p. 457, which solves a host of problems. This technique provides great control over chrominance and luminance and essentially cancels any prospect of “spill” and unwanted reflections.
The latest advances in compositing technology exploit the capacity of computer image manipulation processes and digital film scanning and printing techniques, and have vastly expanded the application and efficacy of composite photography. The catalogue of Petro Vlahos' patents in the field traces the development and increasing sophistication of electronic compositing. While the below listed patents describe the electronic hardware embodiments of the process, these have all now been implemented in computer software for digital electronic composites:
U.S. Pat. No. 3,595,987
U.S. Pat. No. 4,007,487
U.S. Pat. No. 4,100,569
U.S. Pat. No. 4,344,085
U.S. Pat. No. 4,409,611
U.S. Pat. No. 4,589,013
U.S. Pat. No. 4,625,231
In Ultimatte (Vlahos) matte extraction logic, as applied to digital film composites today, the process (while still quite similar), is freed from confinement to the Blue record and readily incorporates garbage and window mattes without any compromise of the finely detailed continuous tone feature.
The starting point for a digital blue or green screen color difference composite is a matte generated by subtracting the value of one color from the value of another for each pixel in the image. (Whether this is accomplished through software or through analog video circuitry, the net effect is the same.)
With Blue logic, the raw matte is a greyscale image whose value at each point is simply the amount by which Blue exceeds the higher of the other two colors. The result is a matte which is dead black anywhere Blue is less than Red or Green and some shade of grey wherever Blue is predominant primary color.
This matte is subjected to a variety of adjustments before it is used to process the foreground and background images, but the crucial point is that the matte is generated from the absolute levels of the color components for each pixel. A pixel having values of 200 Blue, 100 Green and 100 Red will yield a pixel with a value of 100 in the matte while a darker pixel of the same hue with values of 100 Blue, 50 Green and 50 Red will yield a matte value of 50.
In other words, the Ultimatte electronic or digital color difference matting process is a function of the luminance or brightness of the backing as well as the chrominance (hue) or purity of its color and the uniformity or consistency of the matte field.
What emerges quite clearly from this description of how the Ultimatte (and other comparable matte extraction programs) work is that chrom
Juska Cheryl
Liu & Liu LLP
Morris Terrel
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