Chromakeying system

Television – Image signal processing circuitry specific to television – Special effects

Patent

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Details

348586, 348590, 348591, 348592, 382106, H04N 975

Patent

active

061220132

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to methods and apparatus for studio imaging including chromakeying.


BACKGROUND OF THE INVENTION

Background chromakey panels are commonly used in the art of television and video production in order to facilitate merging of a virtual background with foreground figures. The foreground figures are imaged on the chromakey panel background, and the known color of the chromakey panel background is detected and replaced by the virtual background. One problem associated with such productions is that changes in the foreground image, due to camera displacement, pan, tilt and zoom in and out, are not automatically applied to the background scene.
One system designed to solve this problem is the "Virtual Studio" developed by Ultimatte. The "Virtual Studio" requires a special memory head pedestal which measures the camera's pan and tilt angles directly from the camera's mount. A disadvantage of this approach is that in order to obtain a complete perspective transformation for the background image, the zoom state of the lens must be read and the instantaneous location of the camera must be determined. Also, this approach requires that each and every camera mount be replaced by a memory head pedestal, resulting in an expensive system and complicated operation if a large number of cameras are employed. Also, the accuracy of this method is inadequate for seamless foreground/background merging.
Conventional edge detection methods which are based on smoothing and finding directional derivates are described in the following publication, the disclosure of which is hereby incorporated by reference:
Canny, J., "A computational approach to edge detection", IEEE Trans. on PAMI, PAMI-8, No. 6, 1986, 679-697.
Conventional edge detection methods which are based on Hough transforms are surveyed in the following publication, the disclosure of which is hereby incorporated by reference:
J. Illingworth and J. Kitler, "A survey of the Hough transform", CVGIP, 44, 1988, 87-116.
FIG. BA-1 is a simplified block diagram of a state of the art chromakeying system.


SUMMARY OF THE INVENTION

The present invention seeks to provide improved methods and apparatus for chromakeying.
There is thus provided in accordance with a preferred embodiment of the present invention a chromakeying panel for use in conjunction with a chromakeying system having a color keying spectrum, the panel including a plurality of first locations bearing a first color within the color keying spectrum, and a plurality of second locations bearing a second color within the color keying spectrum.
Further in accordance with a preferred embodiment of the present invention the first color and the second color are of the same hue and of different intensities.
There is additionally provided in accordance with a preferred embodiment of the present invention a chromakeying system including a frame grabber operative to grab an image of a foreground image including at least one nonuniform chromakeying panel having a known pattern and a subject, a perspective transformation computation unit operative to compute a perspective transformation by comparing the image of at least one portion of the captured panel with the known pattern, and a background generation unit operative to receive a background image, to apply the perspective transformation thereto and to replace the captured portion of at least one panel with the transformed background, thereby to generate a composite image.
Still further in accordance with a preferred embodiment of the present invention the system also includes a 3D background image source operative to provide the background generation unit with a 3D representation of a background scene.
Additionally in accordance with a preferred embodiment of the present invention the system also includes a background image sequence source operative to provide the background generation unit with a temporal sequence of background scenes and wherein the perspective transformation computation unit is operative in real time relativ

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