JPS636197B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a chromakey device used for inlaying screens in broadcast program production.

Chroma key is a technique that selects a specific color in an image, extracts it, and combines it with another image, and is one of the image special effects commonly used on a daily basis. However, with conventional chromakey devices, the extraction color selection is mainly done by hue (HUE) using Hue Dial, etc.
Although it is a choice, the adjustment is very critical, and there are also factors such as the lighting on the chroma key panel and the deterioration of the temporal characteristics of the camera itself, so it takes time to prepare each time it is used.

The present invention aims to solve these conventional drawbacks and provide a chromakey device that is easy to maintain and adjust. In order to achieve this, the present invention uses a novel color detection process, a chroma key signal generation means based on the process, and a means for specifying a color to be extracted from an image on an image monitor. According to the present invention, the color image signal is sampled and treated as an array in pixel units, so it is particularly suitable for digitized PCM color image signal processing.

FIG. 1 is a block diagram of an embodiment to which the present invention is applied. According to this example, there is an image signal V1 from the camera 1C1 that takes the background of the composite image, and an image signal V2 from the camera 2C2 that takes the subject. By providing a means for generating the cursor and controlling the cursor position from the outside, the sampled color area in the image signal V2 is specified, and a desired composite image is obtained from the images of the camera 1 and the camera 2. The image sequence of is shown in FIG.

Next, details of the present invention will be explained according to this embodiment. The part surrounded by a broken line in the block diagram of Fig. 1 corresponds to the inside of the chromakey device to which the present invention is applied, and 1 generates various timing pulses including the clock pulse CK based on the synchronization signal SY and the color subcarrier signal SC. 2 to 8 are registers that temporarily hold the pixel signals of the encoded PCM image. For example, if quantized to 8 bits/word, 1 word (8 bits)
It has a storage capacity of 2,000 yen, and has two shift registers connected in cascade and driven by a clock pulse CK having the same frequency as the sampling frequency at which the image signal is encoded.
A group is formed. 9 is a keying signal generator which generates pixel signals a ₀ from the register groups 2 to 7,
Keying signal with a ₁ , a ₂ , b ₀ , b ₁ , b ₂ as input
Output KEY. Here, the image sampling frequency is set to four times the color subcarrier (4 x _SC ), and the image information held in registers 2 to 4 and the switch SW are connected as shown in Figure 1, circulating through registers 5 to 8. The principle of generating a keying signal by correlation calculation with another image information will be explained.

In order to explain this, FIG. 3 is an enlarged view of a part of the waveforms of the two types of image signals (composite color signals) (in the figure, T _SC is the color subcarrier period).
When viewed locally in this way, the first color image signal
VA and the second color image signal VB can be expressed by the following equation.

VA=Y _A =C _A・sin (θ _A +ωt) (1) VB=Y _B +C _B・sin (θ _B +ωt) (2) Here, Y _A and Y _B are luminance components, C _A and C _B is the saturation component, and θ _A and θ _B are the hue angles from the sample reference axis. Expressions (1) and (2) above are expressed at three sample points t ₀ , t ₁ , t ₂
For each sample pixel level a ₀ , a ₁ , a ₂ , b ₀ ,
If b ₁ and b ₂ are expressed as By solving the above equation, the composite component of the color image signal VA and the color image signal VB can be obtained as shown in the following equation.

From this, the luminance difference △Y between the two signals, and the saturation difference △
C. Find the hue difference △θ: △Y=Y _A −Y _B = 1/2 (a ₀ − b ₀ + a ₂ − b ₂ ) (7) △θ＝θ _A −θ _B ＝sin ^-1 (a ₀ −a ₂ /2C _A )−sin ^-1 (b ₀ −b ₂ /2C _B )(9
), and these difference values are normalized with respect to the color image signal VA, and the correlation function Φ of these two signals is expressed as Φ=(1-△Y/Y _A )・(1-△C/C _A )・(1 −△
θ/2π) (10) If only the last term related to hue is extracted, a keying signal is generated from the hue difference signal of the two signals, and one of the two signals is extracted and used as a color signal, the same chroma key function as in the conventional method is achieved. Furthermore, if it is possible to calculate other saturation and luminance components with the same degree of precision, the characteristics of extracted color detection will naturally improve. Therefore, the following equation is set assuming that areas with very close correlation express the color detection degree independently for each of the three color elements, taking into consideration the visual characteristics.

Φ _k = (1-K ₁・△Y/Y _A )+(1-K ₂・△C/C _A )+
(1 −K ₃・△θ/2π) (11) According to equation (11), the correlation signal Φ _K is expressed by an addition formula in which the difference value of each component is multiplied by the weighting coefficients K ₁ , K ₂ , and K ₃ , respectively. However, for example, a non-additive formula may be used, such as validating the maximum value and minimum value of the three terms, and there is no harm in approximating the correlation using either method. A keying signal is generated based on this correlation signal Φ _k by performing amplification, non-linear level conversion to emphasize a specific signal level region, or imparting hysteresis characteristics. Therefore, if the weighting coefficients K ₁ , K ₂ , and K ₃ are appropriately selected and an optimal means is used to generate a keying signal from the correlation signal, the desired color detection characteristics can be calculated from a plurality of pixel levels. Become.

Actually, based on the above principle, the keying signal KEY
The keying signal generator 9 in Fig. 1 generates the correlation operation operator by connecting arithmetic elements such as high-speed adders and function ROMs that perform complex operations in a pipeline, and generates the correlation operation in real time for each pixel. Performing calculations. One of the inputs of this keying signal generator 9 is connected to registers 2 to 4 that hold the color image signal V2, which is a line signal to be synthesized from the camera 2C2, and the other input is connected to the register 2 to 4 that holds the color image signal V2, which is a line signal to be synthesized. Registers 5 to 7 that hold desired color signals are connected. However, regarding the latter extracted color signal, pixel levels for one cycle are circulated to designate one specific color.

Next, the extraction color designation circuit will be explained.

13 is a cursor signal generator that operates based on various timing pulses such as horizontal and vertical and clock pulses CK from the timing pulse generator 1, and the cursor follows the position designation (H, V) of the joystick JS installed externally. It generates a signal. A mixer 14 mixes the color image signal V2 captured by the camera 2C2 with the cursor signal, and displays the mixed output signal on the screen of the color image monitor M. The cursor signal simultaneously controls the opening and closing of the gate circuit 15 and switches the color image signal V2 only when the cursor appears.
supplied to one end of the Using these, move the cursor to the position of the color area you want to extract from the color image signal V2 using the joy stick operation,
Furthermore, by switching the switch SW to the output side of the gate circuit 15, the extraction reference color signal is stored in the registers 5-8.

Reference numerals 10 to 12 designate color erasing circuits for key back portions which are required during chroma key screen synthesis, particularly in the case of soft chroma key which performs natural screen synthesis using keying signals with gradations, and are already well known in the analog system. 10 is an inverter circuit that inverts only the chroma components of the sampled reference colors stored in registers 5 to 8; 11 is a level control circuit that controls the level to the opposite polarity using the keying signal KEY;
2 adds a level-controlled complementary color chroma signal of the sampled reference color to the color image signal V2 to eliminate unnatural colors in the area where the two images are mixed (dissolved) in chromakey screen composition. This erased color image signal V2' and the color image signal V1 obtained by photographing the background with the camera 1C1 are used as the keying signal.
A composite image signal V _OUT is obtained through a mixer MX that dissolves with KEY. However, in the chroma key that is normally used, since the sampling color is one color on the screen, it is natural that there is no need to shift drive registers 5 to 8 and extract each color component many times.
It is clear that it is sufficient to store the color component data in the form of extracted color component data, and that one system of high-speed operators that perform calculations in real time from the pixel level can be simplified. Furthermore, by adding some innovation to the sample method for sampling reference colors, it becomes possible to sample multiple colors at the same time.
In addition, although we have described the method of specifying the extraction position on the screen with a cursor, there are other methods, such as specifying the position on the screen with a light-receiving light pen, which is often used in graphic displays. The method is not limited.

Note that in deriving the correlation function equation shown in Equation 11, the luminance components Y _A and Y _B were treated as fixed values, but
In reality, it has high frequency components, and it is desirable to adopt a better YC separation method that has already been proposed and apply the above-mentioned correlation function formula only to the chromaticity component. Also, for the sake of explanation,
Although each component was calculated from three pixel columns in the horizontal direction, the present invention is not limited to this, and it is sufficient to optimally select the correlation formula and horizontal/vertical pixel settings that satisfy the desired characteristics. Also, the above is 2 on the color vector
Although the color phase relationship of points has been shown in a so-called polar coordinate system of hue and saturation, it is clear that the same thing can be said even if this is replaced with, for example, an orthogonal coordinate system of I and Q axes. In particular, as mentioned above, the sample frequency is 4×
If selected as _SC , each sample point is
Y, I, and Q separation can be performed using a simple demodulation circuit. Therefore, if you are not bound by the detection standard of mainly hue difference used in conventional chromakey, it is possible to
It is sufficient to employ an electric correlation equation that calculates the distance between two points or a value that approximates the distance, taking into account the bandwidth ratio.

As explained above, according to the present invention, R, G,
It becomes possible to create a chroma key device with a new color detection configuration and extraction color specification function that realizes line chroma keying for composite color image signals without requiring a B3 primary color signal. In particular, the extraction color specification according to the present invention is directly specified at a position on the screen to be composited, and the color component at that position is extracted and stored from the image signal of the screen to be composited. There is no concern at all with unstable factors such as differences in lighting, camera conditions, etc.
In this way, sampling color settings are performed in an open loop, and there is a great advantage of semi-automation without having to operate the user dial while monitoring the image monitor or level monitor as in the past. It becomes something that shows one's sexuality.

In addition, chroma key signal generation is calculated from image signal correlation, and the signal level changes depending on the degree of correlation. This is equivalent to the conventional analog soft chroma key, which uses a gradation keying signal and a linear gate to synthesize a natural screen. It is possible to stably obtain a composite screen. Similarly, the color erasing function of the chroma key back, which was devised as an application of the analog soft chroma key, can of course be actively used to convert the hue and saturation of the key back portion, or to use it as a shadow chroma key.

What makes the above image processing possible is that the operating principle of the chromakey device according to the present invention is to utilize the correlation between two types of image signals, and among the two pixel storage columns connected to the correlation calculation operator, This is because a signal processing configuration is adopted in which a pixel array of one sampled reference color is arranged, and a luminance component and chromaticity component are analyzed using the same algorithm for this and a composite image input to the other.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a chromakey device according to an embodiment of the present invention, and Fig. 2 a, b, c, and d are diagrams for explaining the functions of the device.
b is the background image from camera 1C1, c is the composite image of a and b, and d is the image on the color image monitor M with the cursor indicating the position of the color to be extracted from the image of a. . FIG. 3 is a diagram for explaining correlation calculation between two types of color images. C1, C2...Camera, 1...Timing pulse generator, 2-8...Register, 9...Keying pulse generator, 13...Cursor signal generator,
14...Mixer, 15...Gate circuit, MX...
mixer.

Claims (1)

[Claims] 1. A first storage means for dividing and storing a color image signal into pixel units of an integer fraction of a color subcarrier cycle; and a control means for instructing a specific color signal in the color image signal by specifying a position on the screen. , a second pixel group for storing a pixel group of a specific color signal instructed by the means;
storage means; means for reading a plurality of pixels from the first and second storage means and calculating the correlation between the color image signal and the specific color signal to generate a correlation signal; means for generating a keying signal from at least one of signals related to a chromaticity difference and a luminance difference between a color image signal and the specific color signal, and the keying signal is used to generate a keying signal from the color image signal or a signal related thereto. A chroma key device that controls the level of a signal and combines it with other image signals.