Television – Image signal processing circuitry specific to television – Special effects
Reexamination Certificate
1999-09-21
2001-06-05
Lee, Michael H. (Department: 2714)
Television
Image signal processing circuitry specific to television
Special effects
C348S590000, C348S593000
Reexamination Certificate
active
06243143
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to effecting video transitions between video streams.
In editing of video in the creation of a video program, it is often desirable to provide a gradual transition from one video stream to another video stream. For example, in a wipe transition, a line may move across the screen from left to right, with the old scene gradually disappearing at the right while more and more of the new scene appears at the left. In a so-called “iris wipe,” the boundary is an expanding circle, and one video stream appears in an expanding circle, and the other is outside of the circle. A solid color could also be used as one stream to provide an image that gradually appears or disappears across the screen or an image that gradually expands or contracts.
Referring to
FIG. 1
, transitions can be created at a video combiner
10
having a first video input
12
for a first video stream, a second video input
14
for a second video stream, a key input
16
to receive key values indicating how the two inputs are to be combined, and a video output
18
for the output video that is some combination of the two inputs. The video streams include frames (each frame providing an image for a screen) made up of horizontal lines, each of which includes individual “pixels” (picture elements) across the line. Each pixel value includes a number of bit values that describe the color and intensity at that particular pixel at a particular time. New frames are provided at the video rate, e.g., 30 frames per second, and the video streams include sequential digital data describing sequential pixel values for lines of video data in a frame. The pixels for the first and second video streams that are input to combiner
10
are synchronized, as are the associated key values. The key value for a given pixel indicates whether the output for that pixel is the input from one stream or the other stream or a combination of the two.
While a unique key value could be stored and accessed for each pixel in each frame, to reduce bandwidth, a single table of gamma values (also referred to as gradient values herein) can be used. For example, a single table with one value for each pixel can be used to define the wipe over the sequence of frames. In the table, the gamma value essentially indicates the time at which the transition appears at that pixel.
FIG. 2
is a simplified diagram of a table of gamma values
20
for an iris wipe of a square (instead of circular) transition. (A real table for NTSC would have 720 horizontal entries and 480 vertical entries.) As the time goes from frames 1 to 2 to 3 etc, a “threshold” value similarly goes from 1 to 2 to 3 etc (or 1, 1, 2, 2, 3, 3 or 1, 2, 3, 3, 4 to spread things out, though the latter example would not be uniform). The threshold is compared to the value in the table to determine the key value (e.g., a 0 key value meaning all of video stream A, a 100 key value meaning all of video stream B, and a 50 key value meaning equal amounts of A and B) that is fed to the mixer. The key values that are generated cause the video output to switch over from one video input to the other. As the threshold increases, the boundary of the transition provided by use of the
FIG. 2
table expands. The following algorithm employs a direct comparison that provides an abrupt transition as the threshold goes from 0 to 4, as shown in displays
22
,
24
,
26
,
28
,
30
in
FIGS. 3A-3E
, respectively.
If (gradient<threshold)
then wipe=transparent
else
wipe=opaque
“Softness” can be added to the key values generated so that the change from one video to the other is not abrupt but instead is gradual (with decreasing amounts of one video stream and increasing amounts of another) in a discrete number of adjacent pixels as the transition passes a pixel location. For example, the following algorithm can be used to produce a gradual transition region N pixels wide.
If (gradient<(threshold−N) then
wipe=transparent
else if (gradient>=(threshold−N) AND (gradient<threshold) then
wipe=½ *opaque*(1−(threshold−gradient)/N)
else if (gradient>=threshold) AND (gradient<(threshold+N)) then
wipe=½ *opaque*(1+(gradient−threshold)/N)
else if (gradient>=(threshold+N))
wipe=opaque
With this algorithm, the transition from one video stream to the other is linear, though the human eye sees brightness more as a cube root function. Also, the threshold may only be moved on integer pixel boundaries, which can cause abrupt changes in movement when the wipe moves X pixels in Y frames, and X and Y are not multiples of each other.
SUMMARY OF THE INVENTION
The invention features, in general, combining first and second video streams into a combined output video stream by using a gradient table listing gradient values for pixels in a video frame to address a look up table of key values, and combining pixel values of the first and second video streams based upon respective key values read from the look up table.
Particular embodiments of the invention may include one or more of the following features. The video is combined at a video combiner having an input for the first video stream, an input for the second video stream, an input for the key values, and a video output. New key values are loaded into the look up table between frames. The new values loaded into the look up table provide a nonlinear interpolation. The new values loaded into the look up table provide a transition over a noninteger number of pixels per frame. The new values loaded into the look up table provide nonlinear softness on the edges of the transition.
Embodiments of the invention may include one or more of the following advantages. Use of a look up table instead of thresholds permits one to create soft transitions that vary in other than a linear way. The look up table also permits one to move the transition boundary by less than one pixel at one time.
Other advantages of the invention will be apparent from the following description of a particular embodiment thereof and from the claims.
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Fierke John R.
Hatalsky Jeffrey F.
Fish & Richardson P.C.
Lee Michael H.
Media 100 Inc.
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