JPH0347631B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a chroma key device, and more particularly to a key signal generating device.

Prior to the description of the present invention, an example of a digital chromakey device that targets digital video signals of Y, U, and V signal systems will be described with reference to the drawings.

In FIG. 1 showing the overall configuration of a digital chromakey device, 1 indicates foreground color video data.
This is the interface to which FG.VID and background color video data BG.VID are supplied together with their respective timing reference signals TRS. This color video data is the output of the color television camera (R,
For example, the luminance signal Y and color difference signals U and V formed by matrix calculation of (14:
Each component is sampled at a sampling frequency of 7:7). Interface 1 provides each timing reference signal TRS.
It looks at the timing signals (horizontal synchronization signal, vertical synchronization signal, etc.) decoded from the video data, sets the phases of the two color video data FG.VID and BG.VID appropriately, and outputs them to the subsequent stage.

2 is a back color data forming circuit. Back color data is formed from the foreground color video data FG.VID, and this back color data is supplied to the key signal forming circuit 3 and the color canceller 5.

The key signal forming circuit 3 generates a signal corresponding to the back color data and the foreground color video data FG.VID.
A comparison calculation is performed for each sample to generate a key signal of a predetermined level. The key signal itself generated in this way contains many disturbances and cannot be used as is, so the key processor 4 performs waveform shaping processing such as clipping, adjusting the edge timing of the clip output, and adjusting the gain. A key signal KEY is obtained from the key processor 4.

Color canceller 5 uses this key signal KEY
Based on , remove the background color from the foreground color video data FG.VID. For example, when the subject is transparent, the transparent background color is removed. Specifically, the back color data is used as the key signal.
Amplitude modulation is performed using KEY, and the modulated output is subtracted from the foreground color video data FG.VID. This back color removal is done only for the U and V signals; the luminance signal Y is simply passed through.

Foreground color video data FG.VID is supplied to this color canceller 5 via a delay circuit 6. The delay circuit 6 has a delay amount corresponding to the time required for the above-mentioned waveform processing in the key processor 4.

And the output CAN of color canceller 5.
VID and background color video data BG.VID are supplied to the mixer 7, and mixing of the two is performed based on the key signal KEY. This mixing consists of two color video data CAN.VID and BG.
In addition to the method of simply switching and outputting VID, a crossfade method can be used in which the level of one is gradually decreased while the level of the other is gradually increased at the boundary between the two. The output of this mixer 7 is supplied to an interface 9 via a digital filter 8. The digital filter 8 is for adjusting the waveform of the output of the mixer 7.

Interface 9 is color canceller 5
Composite color video data KYD.VID from CAN.VID and digital filter 8, which have been decolorized from CAN.VID
, husband's timing reference signal, and key signal
This is for outputting the KEY to the outside.

Furthermore, a microprocessor 10, a CRT monitor 11, and a console 12 are provided, which translate the user's key input from the console 12 and transmit it to the inside of the system, and perform the calculation processing required in each circuit block. It is designed so that you can get used to it. Color canceller 5 and mixer 7 in the digital chromakey device described above
The configuration of the portion shown in FIG. 2 is as shown in FIG. As an example, consider a foreground 15 in which a subject 14, for example a person, is positioned in front of a back screen 13 painted with a background color, for example blue, as shown in FIG. 3A, and a background 16 shown in FIG. 3B. A back color data DB corresponding to the back screen 13 to be used is generated from the back color data forming circuit 2, and as shown in FIG.
The signal is supplied to a multiplier shown at 17. This multiplier 17
is supplied with a key signal KEY' which has an opposite phase to the key signal KEY, that is, has a gain of 0 in the area of the subject 14. Therefore, as shown in FIG. 3C, data in which the back color exists in the shaded area excluding the subject 14 is generated, and the foreground color video data is
Subtracted from FG.VID in subtractor 18. Therefore, as shown in FIG. 3D, video data corresponding to the subject 14 and from which the back color has been removed
CAN.VID is generated from subtractor 18 and multiplier 19
added to. Also, background color video data
BG.VID is supplied to the multiplier 20 and the key signal
An output from multiplier 20 is amplitude modulated by KEY' and thus has the data of the area of object 14 in background 16 removed, as shown in FIG. 3E. On the other hand, since the key signal KEY is supplied to the multiplier 19, by supplying the output data of the multipliers 19 and 20 to the adder 21, the third
As shown in Figure F, an image in which the subject 14 is embedded in the background 16 and the corresponding output video data KYD.
You can get VID.

Here, a conventional method of forming a key signal will be explained with reference to FIG. First, (U,
V) When the reference point corresponding to the back color on the color difference coordinates is (U ₀ , V ₀ ), the axis created by connecting the origin and this point is the X axis, and the axis perpendicular to it passing through (U ₀ , V ₀ ) Let be the Y axis. If the vector connecting the reference point (U ₀ , V ₀ ) and any (U, V) value represents the contribution to the X and Y axes as x and y, then x = (U - U ₀ ) cos θ + It is expressed as (V-V ₀ ) sin θ y=(V-V ₀ ) cos θ-(U-U ₀ ) sin θ θ=tan ⁻¹ (V ₀ /U ₀ ). Therefore, the conventional method is to define a key signal using a function as shown in the following equation.

K = a _| They will be lined up on the edge.

The key signal K generated in this manner is guided to the key processor 4 and waveform-shaped by a clip circuit. For example, when capturing an image of a foreground 15 in which a transparent tip is placed as the subject 14 in front of the back screen 13, the back color can be seen through the center of the tip, so the outline of the subject 14 as shown in FIG. Correspondingly, a key signal K is generated from the key signal forming circuit 3, which has a high level and a slightly low level in the center. The key signal is, for example, a digital signal with 8 bits as one sample, but in FIG. 5, for convenience of explanation, the signal is shown as an analog waveform. Then, a clip operation is performed using the base clip level BL and the peak clip level PL as threshold levels. In other words, everything below BL is set to a level of 0, and everything above PL is set to a level of 255. As a result, a key signal KEY as shown in FIG. 5B is formed. FIG. 5C shows the key signal KEY' having an opposite phase.

The above-mentioned base clip level BL and peak clip level PL are as shown in Fig. 4, and in the same figure, everything included in the small diamond indicated by 22 is 0, and everything outside the large diamond indicated by 23 is 255. , the diagonally shaded area located between the two is a region where the slope of the key signal is determined. At the boundary from the back screen 13 to the subject 14, the position changes from (U ₀ , V ₀ ) to a position corresponding to the color of the subject 14.

If the UV coordinate system described above is divided into the first to fourth quadrants as shown in FIG. 6, the coordinates when the background color is blue will be included in the fourth quadrant. Therefore, the color difference information of the subject is included in the first, second, and third quadrants. However, in reality, due to the blue reflected light from the back screen, part of the color difference information of the outline of the subject (the shaded area) moves toward the fourth quadrant, as shown at 24 in Figure 6. .

Furthermore, there is a problem in that the hue of the camera output differs from that of the subject due to the frequency characteristics of the television camera. For example, if we take a red comb as an example, the handle (low frequency) part has the coordinates of point A in Figure 6, but
In the tooth portion (high frequency), the camera output moves to point C even though the color is the same. On the other hand, the back screen that can be seen through between the teeth also moves from point B to point D.

In order to prevent erroneous keying from occurring due to the above two phenomena, the base clip level and peak clip level must be set to be smaller than the level difference in the normal case. As a result, the number of levels of the key signal obtained decreases, and the quality of the key signal after waveform shaping deteriorates.

This invention aims to solve these problems. That is, in this invention, all color difference data near the origin of the color difference signal coordinate system is returned to the origin (achromatic color).

An embodiment of the present invention will be described below with reference to FIG.

The color difference data from the input terminal 25 in FIG.
The signal is supplied to the key signal forming circuit 3 via. The achromatic coloring circuit 26 is configured to compare the absolute value of the color difference data with a reference value, and when the absolute value of the color difference data is smaller than the reference value, exchange the color difference data with 0. In FIG. 6, the range of achromatic coloring when P and Q are used as reference values is shown by a broken line. The matrix circuit 27 converts color difference data as shown in the following equation.

U′ V′=1+α, −β −α, 1+βU V α β=−U ₀ /V ₀ =m (arbitrary constant) The conversion expressed by this formula is shown in FIG.
This means converting the color difference data on the circumference indicated by 8 into data on an ellipse 29 circumscribing the circumference at two points. Therefore, the two pieces of data in the X-axis direction are separated so that the color difference data at points E and F on the X-axis are transformed into points E' and F', respectively, as shown in FIG. Become.

Further, in this embodiment, means for compensating the frequency characteristics of the camera is provided between the key signal forming circuit 3 and the key processor 4. First, a contour compensation signal is formed by a second-order differentiator 30 and is supplied to an AND gate 33 via a noise removal circuit 31 in the next stage. The output of the level discrimination circuit 32 is supplied as another input to the AND gate 33, so that a contour compensation signal is generated only for a key signal between the base clip level and the peak clip level. Then, the key signal passed through the delay circuit 35 for phase matching is supplied to the subtracter 34, and the AND gate 33
A contour compensated signal is supplied from the subtracter 34, and a contour compensated key signal can be obtained from the subtracter 34.

As can be understood from the description of the embodiments described above, in this invention, the color difference data near the origin of the color difference signal coordinate system is achromatic, so even if there is a back color due to reflection at the edge of the object, the peak will be removed. There is no need to lower the clip level, and key signals with a sufficient number of levels can be generated. Further, as in the above-described embodiment, if the frequency characteristics of the camera are compensated, a key signal with a large number of levels can be similarly obtained.

Note that the present invention can also be applied when using a color difference signal coordinate system other than the (U, V) coordinate system.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an example of a digital chromakey device to which the present invention can be applied, FIG. 2 is a block diagram showing a partial configuration thereof, FIG. 3 is a schematic diagram used to explain its operation, and FIG. 5 and 5 are schematic diagrams and waveform diagrams used to explain key signal formation,
FIG. 6 is a schematic diagram used to explain problems in key signal formation, and FIGS. 7 and 8 are block diagrams and schematic diagrams used to explain the operation of an embodiment of the present invention. 3...Key signal forming circuit, 4...Key processor, 13...Back screen, 14...Subject, 26...Achromatic coloring circuit.

Claims (1)

[Claims] 1. In a chromakey device having a key signal forming means for determining a reference hue coordinate in a color difference signal coordinate system and forming a key signal according to the distance between the reference hue coordinate and the hue coordinate of an input video signal, When an input video signal is input and the distance between the hue coordinates of the input video signal and the reference hue coordinate is smaller than or less than the reference distance, outputting data indicating that the distance is zero;
When the distance between the hue coordinates of the input video signal and the reference hue coordinate is greater than or equal to the reference distance, data conversion means is provided for outputting data having a value corresponding to the distance; A chromakey device characterized in that an output signal is supplied to the key signal forming means.