Video effects system able to intersect a 3-D image with a 2-D image

A video effects system comprises a graphics generator for generating a three-dimensional image in simulated real time, a digital video effects device for generating a second image and transforming the second image in real time, and a depth combiner for combining the three-dimensional image with the transformed second image to produce an output image that is the intersection of the three-dimensional image and the transformed second image.

BACKGROUND OF THE INVENTION 
This invention relates to a video effects system, and more particularly to 
a system that is able to intersect a 3-D image with a 2-D image. 
Digital video effects (DVE) devices, such as the ADO manufactured by Ampex 
Corporation of Palo Alto, California and the Kaleidoscope manufactured by 
The Grass Valley Group, Inc. of Grass Valley, California, have the ability 
to transform a television image. A basic technique for doing this, as 
disclosed in U.S. Pat. No. 4,875,097 issued Oct. 17, 1989 to Richard A. 
Jackson entitled "Perspective Processing of a Video Signal", is to take 
each two-dimensional image and assign to each pixel three coordinates 
(X,Y,Z). The X and Y coordinates refer to the pixel's position on a flat 
surface, and the Z coordinate refers to the distance from a plane that 
contains the viewer's eye. The Z coordinate is initially set to some 
constant since the viewer is looking straight at a flat image. 
The DVE device then does a three-dimensional transformation on the 
coordinates of each pixel, such as disclosed in U.S. Pat. No. 4,797,836 
issued Jan. 10, 1989 to Francis A. Witek and David E. Lake, Jr. entitled 
"Image Orientation and Animation Using Quaternions". Such a transformation 
is the mathematical equivalent of taking the flat more of the three 
coordinate axes, and then moving in space. This transformation process 
takes the original X, Y and Z coordinates and maps them into a new set of 
coordinates X', Y' and Z'. The transformed image is then projected into 
the X-Y plane. Current DVE devices implement transformation algorithms 
using hardware and are able to work in real time, and the particular 
transform that is effected depends on an operator control, typically a 
joystick. Therefore, as the joystick is moved, the transform changes and 
the image can be rotated and translated. 
FIG. 1 illustrates in simplified block form a digital video effects system 
by which two-dimensional images can be transformed and combined. The FIG. 
1 device comprises sources 2A, 2B of first and second analog video 
signals, VideoA and VideoB respectively. Each video signal represents a 
two-dimensional image that is characterized by a distribution of color 
information over a two-dimensional display plane. The video signals are 
accompanied by respective key signals KeyA and KeyB, which are derived 
from key sources 8A, 8B and represent opacity of the respective images as 
a function of location over the display plane. The video signals and the 
accompanying key signals are applied to converters 12A, 12B, which convert 
the input video signals and key signals into digital form. Each converter 
12 may convert its input video signal into a digital signal that is 
compatible with a standard digital television format, such as the CCIR.601 
format. 
A digital video signal in the CCIR.601 standard is composed of four-word 
packets. Each packet contains two luminance slots, Y, and two chrominance 
slots, C1, C2, multiplexed in the sequence C1 Y C2 Y. The words are up to 
ten bits each and the data rate is 27 million words per second. Thus, the 
luminance component of the video signal is digitized at 13.5 MHz and each 
chrominance component is digitized at half that rate. A signal in 
accordance with the CCIR.601 standard is informally referred to as a 4:2:2 
signal. 
Each converter 12 has four output channels, namely a luminance channel, two 
chroma channels and a key channel. The luminance channel carries luminance 
information in ten bit words at 13.5 MHz, the first chroma channel carries 
information pertaining to one of the chroma components in ten bit words at 
6.75 MHz, the second chroma channel carries information pertaining to the 
other chroma component in ten bit words at 6.75 MHz, and the key channel 
carries key information in ten bit words at 13.5 MHz. The three video 
channels may, if necessary, be multiplexed to provide a 4:2:2 signal. 
The four output channels of converter 12 are applied to a transform section 
14 where the input video signal, representing color as a function of 
position in the display plane, is manipulated in three-dimensions to 
simulate transformation (translation and/or rotation of the 
two-dimensional image) of the image in a three-dimensional space and 
projection of the transformed 2-D image back into the display plane. The 
transformation may be effected by loading the values of Y, C1 and C2 into 
a frame buffer at addresses that depend on time relative to the sync 
signals of the input video signal and reading the values out at different 
times relative to the sync signals of the output video signal, whereby a 
quartet of values C1,Y,C2,Y is shifted to a different location in the 
raster. The key signal is transformed in similar manner. The nature of the 
transform can be selectively altered in real time by use of a joystick 15. 
In the transformation operation, values of depth (Z) relative to the 
display plane are calculated to twenty bits. 
Each transform section has six digital output channels. Three output 
channels carry a digital video signal VideoA' or VideoB', representing the 
projection of the transformed two-dimensional image into the display 
plane, in the same form as the digital input video signal. The fourth 
channel carries the transformed key signal KeyA' or KeyB' in the same form 
as the input key signal. The twenty-bit depth words are each divided into 
two ten-bit components Z1 and Z2, which are carried by the fifth and sixth 
channels respectively at 6.75 MHz. The key and depth channels may, if 
necessary, be multiplexed to provide a signal similar to a 4:2:2 video 
signal. 
The output signals of the two transform sections 14A, 14B are input to a 
depth combiner 16. Combiner 16 combines the transformed video signals 
VideoA' and VideoB' on the basis of the respective key and depth signals 
and generates a combined output video signal VideoC. Combiner 16 also 
combines the transformed key signals KeyA' and KeyB' using well understood 
rules and generates a key signal KeyC, and generates a depth signal 
Z.sub.C whose value is equal to the smaller of Z.sub.A ' and Z.sub.B '. 
Combiner 16 includes a multiplexer that multiplexes the luminance and 
chroma information of signal VideoC such that the output video signal is 
in accordance with CCIR.601. Combiner 16 also includes a multiplexer that 
multiplexes the key and depth signals and provides a signal in a form 
similar to the CCIR.601 format, each packet containing two ten-bit words 
of key and one twenty-bit word of depth in two parts of ten bits each. 
By selection of the transformations that are performed on the two video 
images, each transformed image may have pixels that map to the same X' and 
Y' coordinates, so that the two images intersect. 
FIG. 2 illustrates in simplified form the operations performed by a 
graphics generator, such as the Graphics Factory manufactured by Dubner 
Computer Systems, Inc. of Paramus, New Jersey. The graphics generator 
first generates three-dimensional image data, for example by specifying a 
set of points in space that are to be connected. The points are connected 
by lines, and polygons are thereby defined. The polygons are broken down 
into smaller and smaller polygons, until a set of polygons is obtained 
such that each polygon defines a surface patch that is planar within a 
predetermined tolerance. In this fashion, a data base is created 
containing locations in a three-dimensional space (X,Y,Z) of the vertices 
of polygonal surface patches. 
It is then necessary for the operator to define the direction from which 
the image is to be viewed. If the image is, for example, an ellipsoid, the 
viewing direction might be specified as along one of the axes of symmetry 
of the ellipsoid. This viewing direction is fixed relative to the image. A 
three-dimensional transformation is then carried out on the image data so 
as to displace and orient the image so that the viewing direction lies on 
the Z axis. This is accomplished by use of a software implementation of 
transformation algorithms that are similar to those used by a DVE device 
for rotating and moving an object in three-dimensional space. A lighting 
model is applied to the transformed image so as to generate, for each 
surface patch, a perceived color that takes account of light source, 
viewing direction, surface color and other factors. The image data is 
projected into the X-Y plane by loading the color values, which may be 
defined by one luminance value and two chroma values, into a frame buffer 
using only X and Y values to address the frame buffer. By repeatedly 
reading the contents of the frame buffer, a digital video signal is 
generated representing the image when viewed along the selected viewing 
direction. Also, by creating successive frames in which the image is at 
different locations and/or orientations relative to the Z axis, movement 
of the image can be simulated. However, current graphics generators are 
not able to operate in real time. 
The Graphics Factory has two digital output channels. One channel carries 
the digital video signal in CCIR.601 form. The other channel carries a key 
signal in ten bit words at 13.5 MHz. 
It will be appreciated that the foregoing description is very much 
simplified, but since digital video effects systems and graphics 
generators are known in the art additional description of their operation 
is believed to be unnecessary. 
SUMMARY OF THE INVENTION 
Although a graphics generator calculates values of Z for the transformed 
image, for example for use in hidden surface removal, the output signal of 
the graphics generator does not contain explicit depth information. 
According to a first aspect of the invention, a video effects system 
comprises means for generating a three-dimensional image in simulated real 
time, means for generating a second image, transform means for 
transforming the second image in simulated real time, and combiner means 
for combining the three-dimensional image with the transformed second 
image to produce an output image that is the intersection of the 
three-dimensional image and the transformed second image. 
According to a second aspect of the invention, a video effects system 
comprises means for generating a three-dimensional image in simulated real 
time, means for generating a second image in real time, transform means 
for transforming the second image in real time and generating depth 
information associated with the transformed second image, and combiner 
means for combining the three-dimensional image with the transformed 
second image on the basis of the depth information to produce an output 
image that is the intersection of the three-dimensional image and the 
transformed second image. 
According to a third aspect of the invention, a method for carrying out a 
video effect comprises generating in simulated real time a first video 
signal representative of a three-dimensional image and a first depth 
signal associated therewith, generating in real time a second video signal 
representative of a two-dimensional image, transforming the second video 
signal in real time and generating a second depth signal, and combining 
the first video signal with the transformed second video signal on the 
basis of the first and second depth signals.

DETAILED DESCRIPTION 
FIG. 3 illustrates apparatus similar to that shown in FIG. 1 but in which 
one video source and associated components have been replaced with a 
graphics generator 18 that operates in a manner similar to that described 
with reference to FIG. 2. The graphics generator 18 outputs a video signal 
representing the distribution of color information over a two-dimensional 
field. This video signal is generated in the manner previously described, 
by manipulating information relating to the locations in three-dimensional 
space of surface patches of a three-dimensional object, and is output in 
CCIR.601 form over a first output channel. The 4:2:2 video signal from 
graphics generator 18 is applied to a demultiplexer 20, which 
demultiplexes it into a luminance channel and two chroma channels. The 
graphics generator also has a second output channel, which carries a key 
signal. Further, the Z values calculated by the graphics generator are 
used to generate a twenty-bit depth signal. Since a surface patch would in 
general cover more than one pixel, values of Z for pixels within the 
boundary of the patch are calculated from the Z values for the vertices of 
the patch. These calculations are simplified by the fact that each patch 
is assumed to be planar. Each twenty-bit Z word is divided into two parts 
which are carried by two further output channels respectively. The 
key/depth signals provided by the graphics generator are therefore in the 
same format as the key/depth signals provided by transform section 14. The 
demultiplexed video signal provided by demultiplexer 20 and the key and 
depth signals provided by graphics generator 18 are then combined with the 
output signals of the transform section 14, in similar manner to that 
described with reference to FIG. 1, by use of depth combiner 16. Combiner 
16 produces an output video signal representing an output image 22, such 
as shown in FIG. 4, which is a two-dimensional depiction of the 
intersection of a two-dimensional image 24 with a three-dimensional image 
26. 
By use of the joystick 15 associated with transform section 14, the 
two-dimensional image can be displaced and rotated in real time within the 
three-dimensional space occupied by the three-dimensional image and will 
always slice the three-dimensional image correctly when the two images 
intersect. 
The system shown in FIG. 3 therefore provides a combined 3-D/2-D video 
effect by generating a 3-D image in slow time in a graphics generator, and 
then outputting the 3-D image in real time together with associated depth 
information to a digital video effects device for combining with another 
image to produce an intersection of a solid object with another image. 
The 3-D image provided by graphics generator 18 may be a still image, or it 
may be an image in which movement is simulated by reading out a succession 
of images in real time. 
It will be appreciated that the invention is not restricted to the 
particular embodiment that has been described, and that variations may be 
made therein without departing from the scope of the invention as defined 
in the appended claims and equivalents thereof. For example, if both 
inputs to the combiner were provided by graphics generators, then the 
resulting output image would represent the intersection of two 
three-dimensional images.