JPS59172894A - Chromakey device - Google Patents

Abstract

PURPOSE:To prevent a synthesized picture from being rough and coarse by correcting a key signal having a smooth intermediate region other than an edge of a solid-state element among key signals. CONSTITUTION:When the key signal Ko from a key signal forming circuit is applied to a stretch and clip circuit 30, a key signal Ki having an edge 25 and an intermediate level is formed. This key signal Ki is applied to the 1st and the 2nd detecting circuits 31, 32 and a digital low pass filter 33. A detecting signal of high level is generated at the intermediate region to the output of an AND gate 38 of the detecting circuit 31. An output detecting that the gradient is smaller than a reference value is generated from an FF47 of the detecting circuit 32. The detecting output of the detecting circuits 31, 32 is applied to an AND gate, and a generated output X goes to a high level when the key signal Ki is an intermediate value and the gradient in the change is slow so as to eliminate substantially the high frequency component of the key signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a chromakey device that uses differences in hue to fit a subject in a foreground image into a background image.

[Background Art and Problems Therewith] A foreground color video signal in which a subject is positioned in front of a screen of a predetermined color, for example, blue, and a background color video signal of a background image are supplied, and the outline of the subject is determined from the foreground color video signal. There is a known chromakey device that generates a key signal corresponding to the background, and uses this key signal to form a composite image in which a subject is positioned in front of a background.

Generally, in a digital chromakey device, when an image is given as component signals (luminance signal Y2 color difference signal UV), a reference point (Uo + Vo
) is set in the (U-V) color coordinate system, and a key signal for switching is formed based on this reference point. The key signal is used as a switching signal after being stretched and clipped at two levels (heak clip level PL and hip clip level BL).

In such a digital chroma key device, when the key signal has a value approximately intermediate between the above two levels,
Depth due to the roughness of the key signal may appear in the composite image. Typical examples where the key signal has an intermediate value include the outline of an out-of-focus subject, a transparent object, and smoke. Furthermore, if the illumination when photographing the foreground image is poor, the gain of the key signal is low. Therefore, the stretched key signal is
The increased effect of quantization also makes the background noise much less obtrusive.

In order to remove this noise, it is conceivable to insert a low-pass filter into the signal path of the key signal. However, due to the low-pass filter, the edges of the key signal corresponding to the outline of the subject are blunted. The off frequency is
It is relatively high (for example 3 Jz) and cannot correct the roughness in the intermediate region.

[Object of the Invention] The object of the present invention is to provide a chromakey device that removes roughness in the intermediate region of a key signal, eliminates unevenness in a composite image, and makes the composite image look natural. It is.

"Summary of the Invention" The present invention includes: a first detection circuit that detects that the level of a key signal is in an intermediate region; a second detection circuit that detects that the slope of the level change of the key signal is gentle; 1st
The key signal includes a detection circuit and a circuit for substantially removing high-frequency components of the key signal based on the detection output of the second detection circuit.

``Embodiment'' An embodiment in which the present invention is applied to a digital chromakey device that targets digital video signals of Y, U, and V signal systems will be described below.

In FIG. 1 showing the overall configuration of the digital chromakey device, 1 indicates foreground color video data FG, VID.
and background color video data BG, VID
are the interfaces provided with the respective timing reference signals TR3. This color video data is
Color television camera output (R, G.

It is made up of components obtained by sampling the luminance signal Y, the color difference signals U and V, which are formed by matrix calculation of B), at a sampling frequency of, for example, a ratio of (14 near-near). The interface 1 receives timing signals (
(horizontal synchronization signal, vertical synchronization signal, etc.), the phases of the two color video data FG, VID and BG, VID are set to be appropriate, and the phases are output to the subsequent stage.

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

The key signal forming circuit 3 generates reference points (Uo, Vo) corresponding to bank colors and foreground color video data FG, VI.
A comparison operation is performed for each corresponding sample with D, and a key signal of a predetermined level is generated. 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 this clip output, and adjusting the gain. , a key signal KEY is obtained from the key processor 4. In this key processor 4, the intermediate region of the key signal is corrected as will be described later. .

The color canceller 5 removes the back color from the foreground color video data FG and VID based on this key signal KEY. For example, when the subject is transparent, the transparent background color is removed.

Specifically, the back color data is amplitude-modulated using the key signal KEY, and the modulated output is used as the foreground color video data FG.
, VID. This back color removal is done for the U and V signal blocks,
The luminance signal Y is simply passed through.

The color canceller 5 is supplied with foreground color video data FG, VI'D 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.

Then, the output CAN of the color canceller 5, VI
D and the background power 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 involves two color video data CAN, VID and BG, VI.
In addition to the method of simply switching and outputting D,
At the boundary between the two, a cross-fade method can be used in which the level of one is gradually decreased while the level of the other is gradually increased. The output of this mixer 7 is passed through a digital filter 8 to an interface 9.
supplied to The digital filter 8 is used to adjust the waveform of the output of the mixer 7.

The interface 9 is for outputting the achromatic CAN and VID from the color canceller 5, the composite color video data KYD and VID from the digital filter 8, their respective timing reference signals, and the key signal KEY to the outside. It is something.

Furthermore, a microprocessor 10. A CRT monitor 11 and a console 12 are provided, and it is possible to translate the required key human power from the console 12 and transmit it to the inside of the system, and to perform the calculation processing required in each circuit block. ing.

The configuration of the color canceller 5 and mixer 7 in the digital chromakey device described above is as shown in FIG.

In the back color data forming circuit 2, bank color data DB corresponding to the back screen to be used is formed and supplied to a multiplier shown at 18 in FIG.

This multiplier 18 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 region of the subject. Therefore, data in which the back color exists in an area excluding the subject part is generated, and the foreground color video data FG is generated.

It is subtracted from VID in subtractor 19. As a result, video data CAN and VID corresponding to the subject and from which bank colors have been removed are generated from the subtracter 19, and the video data CAN and VID are generated from the subtracter 19, and
Added to 0. Still background color video data BG,
VID is supplied to the multiplier 21, and the key signal KEY'
An output is produced from the multiplier 21 which is amplitude modulated by , and thus has the data of the object region removed in the background.

On the other hand, since the key signal KEY is supplied to the multiplier 20, the output data of the multipliers 20 and 21 is sent to the adder 22.
output video data KYD and VID corresponding to an image in which the subject is embedded in the background can be obtained.

Here, an example of a method for forming a key signal will be explained with reference to FIG. First, (U.

■) Set the reference point corresponding to the bank color on the color difference coordinates (U
O, VO), the axis formed by connecting the origin and this point is the X axis, and the axis perpendicular to it and passing through (UOI Vo) is the Y axis. Reference point (Uo, Vo) and arbitrary (U.

■) Express the contribution to each of the X and Y axes as x + y with a vector connecting the values! = ([J −TJo)CQSO+(V −Vo)
Si, nθy −(V−Vo) cosθ−(U−Uo
) Sih, θθ=jan (0/UO). Therefore, the key signal is defined by a function as shown in the following equation.

K=a I x I+b I y 1 (a, b are any positive constants.) When K on the left side is set to a constant value, it is satisfied (U
, V) values will be arranged on the sides of the diamond.

The key signal generated in this way is processed by the key processor 4.
is guided, stretched, and waveform-shaped by the Kritzo circuit. For example, if you take an image of a foreground with a transparent tip placed as a subject in front of a bank screen, the back color will be visible in the center of the tip.
A key signal K that has a high level corresponding to the contour of the subject and a slightly low level in the center is sent to the key signal forming circuit 3.
arises from The key signal is, for example, a digital signal with 8 bits as one sample. The waveform of this key signal is then stretched and subjected to a clipping process in which the base clipping level BL and peak fringe level PL are set to 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 from which bank ground noise has been removed is formed.

” The base clip level BL and the peak clip level PL of the two series are shown in Fig. 3, and in the same figure, everything that is included in the small diamond indicated by 23 is outside the large diamond indicated by 0.24. are all set to 255, and the portion located between the two becomes an intermediate level region that determines the slope of the key signal. At the boundary from the back screen to the subject, the position changes from (UO+VO) to a position corresponding to the color of the subject.

The intermediate level correction circuit provided in the key processor 4 will be explained with reference to FIG.

In FIG. 4, 30 is a key signal K from the key signal forming circuit 3. is a stretch and clip circuit supplied with - As an example, when the subject is a glass tip, the key signal relationship is as shown by Ko in FIG.

FIG. 5 shows the change in the key signal from the contour of one side of the tip to the center, and also shows the key signal as an analog waveform.

In the stretch and clip circuit, it is stretched and, for example, (PL=192 quantization levels.

BL=15 quantization level), and as shown in FIG.
1 is formed in the key signal having an intermediate level corresponding to the edge 25 rising to the 56 quantization level and the transparent portion in the center.

This key signal of 1 is supplied to the first detection circuit 31, the second detection circuit 32, and the digital low-pass filter 33. The first detection circuit, path 31, consists of a comparator circuit 34.35 whose key signal is supplied with a 1, a flip-flop 36.37 and an AND gate 38. The comparison circuit 34 is supplied with reference data PL1, and when the value of the key signal is smaller than the reference data PL, a high level comparison output is generated. The comparison circuit 35 is supplied with reference data BL+, and generates a high-level comparison output when the value of 1 in the key signal is greater than the reference data BLl. flip flop 3
6.37 operates with a sample clock and is only used to remove comparison amount cut transients (whiskers). The AND gate 38 of this detection circuit 31 generates a detection output that becomes high level when the value of 1 in the key signal is in a range (intermediate region) that is greater than BL+ and smaller than PL+.

The detection circuit 32 includes a latch 41, a subtracter 42, and a latch 43.
, ROM 44, latch 45, comparator 46, and control flop 47. The illustration of the sampling clock supply path to the latch and the Noritub flop is omitted.

In the subtracter 42, the value of one sample before is subtracted from the current sample value of one to the key signal, and the change in value of two consecutive samples is extracted. Changes in this value are ROM 4
4, it is converted into an absolute value and supplied to the comparator 46,
It is compared with reference data UL. From the comparator 46,
A comparison output that becomes high level is generated when the difference between two consecutive sample values is smaller than the reference data UL (for example, 64 quantization levels). This comparison output is the Noritsu flop 4
7 as a detection output. Detection circuit 32
Detects that a level change (influence) of 1 in the key signal is smaller than the reference value.

The detection output of the detection circuit 31 is supplied to an AND gate 49 via a shift register 48 for phase adjustment. The detection output of the detection circuit 32 is still supplied to the AND gate 49. The detection signal X generated from this AND gate 49
1 is the intermediate value of the key signal, and becomes high level when the change is gradual.

The low-pass filter 33 includes latches 61 and 62.

63, 64, 67, 68, 69 and an adder 10.71. Further, latches 65 and 66 are further connected to the cascade connection of latches 61 to 64. The detection signal X passed through the phase matching shift register 50 is supplied to the output control terminal of the latch 66 at the final stage. Still the last stage latch 6 of the low pass filter 33
A detection signal X from a shift register 50 is supplied to the output runt roll terminal of 9 via an inverter 51.

When the key signal K has an intermediate value and changes slowly, the detection signal X becomes high level and the latch 69 generates an output. On the other hand, when the above-mentioned conditions are not satisfied and the detection signal X is at a low level, the latch 66 generates an output. latch 6
For example, the output of I M
On the other hand, the output of the latch 66 passes through the launch 61 to the latch 66 and has no frequency characteristics. The key signal 2 outputted from the latch 66 or latch 69 is passed through the digital low-pass filter 52 and outputted to the output terminal 53 as the key signal 3. The cutoff frequency of this low-pass filter 52 is set to be as high as about 3 fvlHz.

Still, in one embodiment of the invention, the low pass filter 33
An adder 72 is provided before the latch 67 that constitutes the
For this adder 72, constant data CL (for example, 6
4 quantization levels) are provided. Therefore, the output of the low-pass filter 33 appearing from the latch 69 has its value shifted by the constant data CL. The value of this constant data CL is made variable by a digital switch or the like.

When a 1 appears in the key signal shown in FIG. 5A from the stretch and clip circuit 30, a 2 in the key signal shown in FIG. 5A is supplied to the low pass filter 52. An intermediate region of 1 in the key signal excluding the edge 25 corresponding to the contour is subjected to band-limiting processing by the low-pass filter 33, and 2 is generated in the key signal level-shifted by constant data CL.

By passing the key signal 2 through the low-pass filter 52, the key signal 3 shown in FIG. 5B is obtained.

If the processing according to the present invention is not performed and the key signal 1 is directly supplied to the low-pass filter 52, the key signal indicated by h in FIG. 5B is extracted. As is clear from comparing the key signal 3 and the key signal 4, the value of the key signal 4 changes more rapidly than the key signal 3, and the key signal 4 is rough.

Note that a digital filter 54 having a configuration as shown in FIG. 6 may be used as the low-pass filter 33. This digital fill 54 is 73.74.75
．． 76 and 77 are connected in cascade, and the input of the launch 73 and the output of the latch 74 and the output of the lunch 76 are supplied to the adder 78, and the transfer function is (H(z)-z-' + '
z-2+1).

"Effects of the Invention" This invention corrects the smooth middle region of the key signal other than solid edges, thereby preventing the roughness of this part from appearing as irregularities in the composite image. can.

Further, as in the above-described embodiment, the configuration of shifting the value of the intermediate region of the key signal can adjust transparency to a preferable value and prevent faint smoke from disappearing.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the present invention, FIG. 2 is a block diagram of the color canceller and mixer, FIG. 3 is a route diagram used to explain the formation of key signals, and FIG. 5 and 5 are block diagrams showing the configuration of the main parts of an embodiment of the present invention and graphs used to explain the invention, and FIG. 6 is a configuration diagram of an example of a digital filter that can be used in the present invention. . 3...Key signal forming circuit, 4...Key processor, 7...Mixer, 30.
...Stress check and clip circuit, 31...
...First detection circuit, 32...Second detection circuit, 33.52...Digital low-pass filter. Agent Masato Sugiura

Claims (1)

[Scope of Claims] A chroma key device that forms a key signal from a foreground color video signal and synthesizes the foreground color video signal and background color video signal based on the key signal, wherein the level of the key signal is a first detection circuit that detects that the key signal is in the intermediate region; a second detection circuit that detects that the slope of the level change of the key signal is gentle;
With the detection output of the detection circuit and the second detection circuit,
A chromakey device comprising: a circuit that substantially removes high-frequency components of the key signal.