Television – Image signal processing circuitry specific to television – Special effects
Reexamination Certificate
1999-09-02
2002-10-22
Hsia, Sherrie (Department: 2614)
Television
Image signal processing circuitry specific to television
Special effects
C348S598000, C348S650000
Reexamination Certificate
active
06469747
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to image processing, and more particularly relates to a system and methods for mixing two independent signal sources while smoothly controlling the rate of change during mixing, especially useful in scene-by-scene color correction systems, matte mixing, and “blue screen” video masking applications.
BACKGROUND OF THE INVENTION
Video signal color correction systems for creating, enhancing, compressing, filtering, or otherwise modifying characteristics of video images are known in the art. Systems for modifying video signals are used for creating special effects as well as for correcting video images to compensate for variations in cameras, film, lighting conditions, etc.
Video image processing systems are especially employed in post-production color correction systems for motion picture film and/or video tape color corrections, and typically operate on a scene-by-scene basis. A “scene” is a sequential collection of images, often shot from the same camera, having the same viewpoint, composed in a certain way, etc. An operator using a typical post-production color correction system observes a target frame of a scene on a video monitor, adjusts the color or other parameters of the frame until it is aesthetically satisfactory, and stores color correction parameters in system memory. The color correction system preferably automates the application of the stored color correction parameters to the other frames of the scene.
In many applications, color correction is applied to selected regions of a video image. Various methods are employed to isolate color regions or geometric regions for receiving color corrections. A color correction system that isolates regions by color or hue is described in U.S. Pat. No. 6,337,692 entitled “Primary Color Manipulation Using Hue, Saturation, Luminance and Area Isolation.” The system described in this patent isolates one or more color correction regions through operations performed in the hue domain. The regions for receiving color correction or modifications are defined through “qualification”. Specifically, parameters of hue qualification, saturation qualification, luminance qualification, and an optional alpha filter are combined to define an alpha qualification function that isolates a region or “hue sector” for color correction. The alpha qualification function may have a shape in the hue domain that ramps or softens the applied color correction by generating a gradual or fractional transition towards the edges of the corrected hue sector.
It is also known in the art to define geometric regions for receiving color corrections. For example, U.S. Pat. No. 6,097,853 entitled “User Definable Windows for Selecting Image Processing Regions,” describes a system where a user of an image processing system such as a scene by scene color corrector can define a window or region for purposes of applying image processing only to selected regions of an image. A geometric region can consist of a square, rectangle, triangle, or a composite geometric region defined using tools.
Color corrections can be effected for regions inside a defined window or regions outside the defined window. Furthermore, separate sets of color corrections can be defined for regions inside the window and outside the window. Utilization of windows for defining regions for receiving color correction is also called “masking”, and the window is often called a “mask” or “matte”. Masking can be effected both with color region isolation or with geometric windows.
A matte or mask can be set up so that the regions inside the matte receive one set of color corrections, while regions outside the matte receive a different and second set of color corrections. As in the case of detecting a hue region for color correction with qualification, the boundaries of a window (or mask or matte) are often softened electronically with a gradual fractional application of color correction so that the transition between regions that receive different color corrections is not as noticeable. Stated in other words, color corrections in a transition region are gradually diminished or increased, as appropriate, between the inside and the outside of the matte.
The basic color masking technique is often employed in “blue screen” applications to create special effects. A “blue screen” application is when a camera shoots a scene with an actor positioned before a blue screen, with the system creating a “mask” defined by the blue color. It is known in the video and film arts to shoot an actor in front of a having a predetermined blue color to derive a first video signal, provide a second video signal containing a background image against which the actor is to be superimposed, and to mix the first video signal with the blue screen with the second video signal. A color correction system detects regions of the first video signal containing the predetermined blue hue and adds or mixes in the second video signal in such detected regions. The effect is an overlay of the actor over the scene represented in the second video signal. In this manner, the actor can be made to appear superimposed over a different and independent image, e.g. a weather map, a scene from outer space, flying over the ocean, etc.
The blue screen technique is also known as “keying”, in the sense that the first video signal with the blue region serves as a key, and the second video signal provides a signal source that is substituted for the predetermined values of blue as detected in the circuit. Another term used by those skilled in the art is “matte”.
When conducting color correction operations, including keying, matting, and blue screen methods, it is generally necessary to mix two independent video signals to arrive at a combined video signal. In some applications, the two mixed video signals each contain a key or matte. A video signal mixer is usually employed to effect this mixing function.
Refer now to
FIG. 1
for an example of mixing a first video signal containing a first key or matte and a second video signal containing a second key or matte. A first video image
12
containing a geometric matte or key
14
with a fractional boundary or transition zone
16
is to mixed with a second video image
20
containing a second matte or key
22
with a second fractional boundary or transition zone
24
. The desired result is a third video image
30
where the two mattes
14
,
22
are combined.
Assume further that the peripheral edges
16
,
24
of the keys
14
,
20
are fractionalized, i.e. the boundary between regions of the video image inside the key and outside the key experiences a tapering off of the application of color correction. Color correction applied to regions inside the key gradually tapers to zero in the fractionalized areas. Conversely, color correction applied to regions outside the key (if any) gradually tapers to zero in the fractionalized area.
The video images in
FIG. 1
are “windowing” signals in the context of video signal color correction signals. A windowing signal is a gray scale signal in that it goes from white (0) to black (1) with a number of fractional (gray) values in between as it transitions. The fractional values occur in the peripheral edges
16
,
24
of the keys
14
,
20
. A window signal of white (0) would produce a color correction pertaining to an OUT-WINDOW set of color corrections as defined by the user, and a window signal of black (1) would produce an IN-WINDOW set of color corrections at the output. Any fractional window value (between 0 and 1) would produce a mixture of the IN-WINDOW and OUT-WINDOW sets of color corrections.
When mixing mattes that include fractional transition zones or regions, artifacts can occur where there are discontinuities between the fractional values defining the transitions. These discontinuities are most likely to occur in applications where two or more mattes are combined to form a larger composite area, such as shown in
FIG. 1
at
32
, which is the intersection between the window or matte
14
and the window or matte
22
.
Gibson Joel D.
Rai Sanjay Devappa
Da Vinco Systems, Inc.
Hsia Sherrie
Morris Manning & Martin LLP
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