Facsimile and static presentation processing – Static presentation processing – Attribute control
Patent
1983-06-13
1986-05-13
Chin, Tommy P.
Facsimile and static presentation processing
Static presentation processing
Attribute control
H04N 522, H04N 9535
Patent
active
045890137
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
Electronic combination of separate foreground and background scenes into a composite whole picture.
BACKGROUND ART
The earliest video compositing devices to be put into service are generally known as "chroma-key" and were described by Kennedy and Gaskin of the National Broadcasting Company in the Dec. 1959 issue of the "Journal of the Society of Motion Picture & Television Engineers", pgs. 804 to 812.
The basic principle of all chroma-key devices is to develop a keying or switching signal based on the presence or absence of a backing color such as blue. The key signal is used to switch video from the background scene to the foreground scene when the foreground camera scanning beam leaves the blue backing and enters the subject area, and vice versa.
Recently, Nakamura et al modified the chroma-key system to a "soft edge chroma-key", in which the edges between the foreground and the background are purposely blurred. This tends to hide the hard edge effects of switching between the foreground and the background. However, detail is lost in the boundary area, and since individual strands of hair represent such a boundary area, they are not reproduced. Nakamura also added a subtraction circuit to eliminate the blue at the soft edge. The system is disclosed in the SMPTE Journal, Vol 90, No. 2, Feb. 1981, page 107.
Another recent modification of the chroma-key system is described by Mason of the British Broadcasting Corporation in UK patent No. 2,044,036, published Oct. 8, 1980. It also removes the blue tint in the soft edge of the switching region.
All chroma-key (i.e., switching devices) including the Nakamura and Mason soft edge devices suffer from a number of defects, among which are the loss of fine detail, such as hair, netting, lace, etc., and the inability to faithfully reproduce a full linear range of semi-transparent subjects.
The scanning beam in a switching system must be part way into the subject in order to develop sufficient information to determine that a switch action should occur. That portion of the subject covered by the scanning beam prior to switching is forever lost. No chroma-key device can therefore reproduce the foreground subject without loss of edge detail. This is why such devices cannot reproduce individual strands of hair.
A switching device cannot adequately reproduce a semi-transparent subject, since a switch is an "OR" device. That is, it shows either the foreground `or` the background scene through it. The visibility of the background scene should be reduced in luminance in proportion to the opacity of the foreground subject.
To accomplish this `and` combining of the foreground and background scenes it is necessary to keep the foreground video channels open at all times and at full level, so as to show all levels of the foreground subject transparency down to the smallest wisp of fog or clear glass. However, if the foreground channels are open the blue backing must be removed by suppression, not by switching. Further, the control of the background level must be linear; that is, proportional to the brightness and visibility of the colored backing. Proportional control of the background level not only results in realistic reproduction of transparent objects, it also causes retention and transfer of shadows from the backing to the background scene.
A non-switching compositing system, having the foreground channels always `on`, will retain the limiting resolution of the camera, and no detail will be lost.
The P. Vlahos U.S. Pat. No. 3,595,987 was filed Feb. 20, 1969. It introduced the concept of developing a control signal proportional to the brightness and visibility of the colored backing, of controlling the level of the background scene as a linear function of the amplitude of the control signal, and of eliminating the blue backing by limiting that video signal amplitude to a maximum that is represented by the instantaneous amplitude of one of the other primary colors. This limiting action also eliminated lens flare and discoloration of foreground subjects by s
REFERENCES:
patent: 3560638 (1971-02-01), Skrydstrup
patent: 3595987 (1971-07-01), Vlahos
patent: 3778542 (1973-12-01), Hanseman
patent: 4007487 (1977-02-01), Vlahos
patent: 4100569 (1978-07-01), Vlahos
patent: 4344085 (1982-08-01), Vlahos
patent: 4409611 (1983-10-01), Vlahos
High Quality Montage Pictures by a New Color Killer Soft Chromakey System, by Nakamura et al. SMPTE Journal, Feb. 1981, vol. 90, pp. 107-112.
Fellinger David F.
Vlahos Paul E.
Vlahos Petro
501 Ultimatte Corporation
Chin Tommy P.
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