Television – Image signal processing circuitry specific to television – Special effects
Reexamination Certificate
1999-03-18
2002-02-19
Eisenzopf, Reinhard J. (Department: 2614)
Television
Image signal processing circuitry specific to television
Special effects
C348S584000, C348S586000, C348S590000, C348S591000, C348S592000, C348S599000, C345S111000, C345S111000, C345S426000, C345S440000
Reexamination Certificate
active
06348953
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an apparatus allowing the composition of two images according to the so-called “blue-screen” method.
2. Description of the Prior Art
As disclosed in U.S. Pat. No. 4,100,569, one of the two images—henceforth also called the foreground image—here shows an object or a three-dimensional scene with a substantially monochrome, preferably blue, background. The difference in color allows to separate the object or three-dimensional scene and the blue background.
The other image—henceforth also called the background image—on the other hand shows an arbitrary background into which the object or three-dimensional scene of the foreground image is to be transferred. This way it is possible to, for example, film a TV moderator with a blue background in a TV Studio, and to subsequently transfer this scene into an arbitrary setting, recorded previously as a separate image.
To this end, the known apparatus calculates two control parameters for each scanning point based on the chromatic values of the foreground image, wherein the first control parameter (“background control voltage”) specifies how intensely the background image is to be shown in the resulting image—henceforth also called the composite image, whereas the second control parameter (“clamping voltage”) specifies to which degree the color of the blue background must be attenuated in the composite image in order to suppress the unwelcome color contribution of the blue background.
The composite image is then combined by a TV mixer from the chromatic values of the background image weighted by the first control parameter on the one hand, and from the chromatic values of the foreground image on the other hand, wherein the blue color component of the foreground image is attenuated according to the second control parameter.
It is important in this context that the color components of the foreground image are taken into account in each scanning point in the mixing of the composite image. Thus, the foreground image is not subject to a switching process assembling the composite image of either the chromatic values of the foreground image or of the chromatic values of the background image. On the other hand, this allows to also reproduce semi-transparent objects in the foreground image, which in the composite image have the new background shine through instead of the blue background. On the other hand, this way the optical resolution of the foreground image is totally conserved.
The more recent U.S. Pat. Nos. 5,424,781; 5,343,252; 4,625,231; 4,589,013 and 4,344,085 describe sophistications of the method described above, wherein essentially the formulas for determining the two control parameters are modified by taking into account several correction factors. The object is to produce an optically satisfying composite image even for difficult color compositions of the foreground image.
The methods disclosed in the above documents thus allow the composition of two images to give composite image according to the “blue screen” method, however, especially for certain spectral compositions of the foreground image, they result in a composite image that appears optically unnatural. For professional use, e.g. to produce special effects in the film industry, this makes a costly manual touching up of the composite image necessary.
Additionally, the documents cited above, particularly U.S. Pat. No. 4,589,013, disclose the so-called “chroma-key” technique. This technique also renders the composition of two images to give a composite image. However, as opposed to the method described in the beginning, with the chroma-key technique the individual scanning points in the composite image are composed either of the color components of the foreground image or of the color components of the background image. Thus, the foreground image is subject to a switching process. Because of the analog image encoding this results in an accordingly reduced optical resolution and complicates a reproduction of semi-transparent objects.
SUMMARY OF THE INVENTION
Accordingly, the object of the invention is to create an apparatus and/or a method to combine a foreground image and a background image to give a composite image with a natural optical appearance, wherein the foreground image pictures an object or a scene with a substantially monchrome background.
The invention is based upon the insight that the deterioration of the optical resolution, usually entailed by composing the composite image either of the pictorial content of the foreground image or of the pictorial content of the background image, no longer ensues, if the image processing is done digitally and if the separation of the foreground image into object on the one hand and monochrome background on the other hand is done for each pixel individually.
The present invention thus covers the art of providing both the foreground image and the background image in digital form, and of composing the composite image in each pixel either of the chromatic values of the corresponding pixel of the foreground image or of the chromatic values of the corresponding pixel of the background image, the composite image being subsequently processed by an image processing unit in order to reproduce e.g. transparency effects.
The term chromatic value as used here and below is to be interpreted broadly and just means that the pictorial appearance of a pixel can be calculated from its chromatic values(s). In the preferred embodiment of the invention, however, the chromatic values represent the intensity of the three primary colors red, green and blue, following the well known RGB color scheme. They are represented by numbers between 0 and 255, a high number standing for a high intensity of the corresponding color component.
Also the term monochrome background with which the object or scene in the foreground image is depicted is to be interpreted broadly. Monochrome does not imply each pixel in the region of the background has exclusively one color component, whereas the other two color components are zero. Decisive is rather the predominance of the intensity of one component—preferably blue—over the other two color components as well as that the color composition within the image region forming the background varies as little as possible.
A first processing unit subdivides the foreground image into object or scene and monochrome background. It calculates a control signal for each pixel, based both on the chromatic values of the foreground image and on predetermined chromatic values representing the color composition of the monochrome background. The control signal reflects whether a given pixel is part of the object and/or scene or part of the monochrome background.
A selection unit assembles the composite image. It calculates the chromatic values of each pixel, based on either the chromatic values of the corresponding pixel of the foreground image or on the chromatic values of the corresponding pixel of the background image.
When subdividing the object and/or scene and the background in the foreground image it is important that the predetermined chromatic values, representing the color composition of the monochrome background, reflect the actual color composition of the monochrome background as accurately as possible. However, this is difficult to accomplish since the foreground image often is available as a digitized photography only. Thus, the user has no information on the color composition of the monochrome background utilized in the photography.
In one embodiment of the invention it is therefore intended to establish the color composition of the monochrome background by calculating the average of the individual color components within the entire foreground image. The numbers thus calculated are in rather good agreement with the actual chromatic values of the monochrome background especially if the object or scene takes only little space in the foreground image, while the greater part of the foreground image is taken up by the monochrome background. However, because
Eisenzopf Reinhard J.
Natnael Paulos M.
Norris McLaughlin & Marcus P.A.
Zbig Vision Gesellschaft für neue Bildgestaltung mbH
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