JPS6238663B2 - - Google Patents

Description

[Detailed description of the invention]

This invention calculates the correlation coefficient between a pre-stored reference screen and a newly input screen in images supplied from a television camera or an infrared imaging device, detects the maximum correlation point, It relates to a device for tracking a desired target or scene. In conventional devices of this type, α
On the screen that has been analog-to-digital converted with bits (α≧1), horizontal and vertical correlated screens 1 and 2 are provided in a cross shape with a width of m pixels (m≧1), and a length of n pixels (n≧1) in each direction. The small areas of 1) were provided as reference screens 3 and 4, and the correlation coefficients C(x) and C(y) were determined by scanning the reference screens in the horizontal or vertical direction on the correlated screen. The above correlation calculation is executed in both the horizontal and vertical directions independently of each other and according to the same algorithm, so the horizontal direction will be explained below as an example. In FIG. 1, the video signal of correlated screen 1 is
(i・j), the video signal of reference screen 3 is R(i・j)
Then, the correlation coefficient C'(x) is given by equation (1). Here, i and j are coordinates in the X-axis and y-axis directions when the upper left end of the reference screen 3 is taken as the coordinate origin. By the way, when performing correlation processing on images supplied from a normal television camera or an infrared imaging device, the above P(i+x,j) and R(i・j) are expressed as shown in equations (2) and (3). DC component Po, AC component Ro
Pm(i+x,j) and Rm(i・j) are superimposed. P(i+x,j)=Po+Pm(i+x,j) (2) R(i・j)=Ro+Rm(i・j) (3) In conventional devices of this type, the correlation coefficient is calculated using equation (1). Since we were looking for C′(x), we needed the required correlation coefficient as shown in equation (4).

[Formula] becomes the DC component PoRo that reduces the signal component of the correlation coefficient and the noise component of the correlation coefficient. are superimposed, so the signal-to-noise power ratio of the correlation coefficient (hereinafter referred to as SNR) decreased, and tracking accuracy was low. As described above, since the tracking accuracy changes in accordance with changes in the DC component superimposed on the video, it is difficult to perform stable tracking, especially when used outdoors where brightness changes rapidly. In order to eliminate this drawback, the present invention calculates the average value of the video signal of the correlated screen in each horizontal and vertical direction, subtracts this average value from the video signal to extract only the AC component, and then extracts the AC component from the extracted correlated screen. The correlation coefficient is determined using a video signal of a reference screen cut out from one portion and stored in a memory in advance. A detailed explanation will be given below with reference to the drawings. FIG. 2 is an enlarged view of the correlated screen 1 and the reference screen 3 in the horizontal direction of FIG. In FIG. 2, the correlated screen 1 has a width of m pixels and a length of W pixels, and the reference screen 3 has a width of m pixels and a length of n pixels, and the video signals of each screen are P(i+x,
j) Let R(i・j). Now, if Po and Ro are the average values of the video signals of the correlated screen and the reference screen, then they are given by equations (5) and (6). Here, by subtracting the DC components Po and Ro from P(i+x・j) and R(i・j), the AC components Pm(i+x・j) and Rm(i・j)
Only equations (7) and (8) remain. Pm(i+x・j)=P(i+x・j)−Po (7) Rm(i・j)=R(i・j)−Ro (8) The above correlated signal Pm(i+x・j) and reference signal Rm When the correlation coefficient C(x) with (i.j) is determined according to equation (1), equation (9) is obtained, and only the required correlation coefficient can be obtained. FIG. 3 shows a comparison between the correlation coefficient C(X) obtained using the apparatus according to the present invention and the correlation coefficient C'(x) obtained using a conventional apparatus of this type. As can be seen from equations (4), (9), and Figure 3,
If the coordinate at which the correlation coefficients C(x) and C'(x) are maximized is Xp, then in conventional devices of this type, the correlation coefficient C'(x) becomes a DC component as it moves away from Xp.
In contrast, in the device according to the present invention, the correlation coefficient C(x) asymptotically approaches 0, and the DC component
The signal component increases only in PoRo. On the other hand, in conventional devices of this type, is superimposed, so the video signal Pm(i+x・j)
and Rm((i・j) directly appears in the correlation coefficient, and the correlation coefficient C′(x) becomes noise-like. However, in the device according to the present invention, the correlation coefficient C(x) becomes smooth. As described above, the correlation tracking device according to the present invention can eliminate the decrease in the SNR of the correlation coefficient due to the DC component of the video signal and the fluctuation in the SNR due to fluctuations in the DC component. Stable tracking is possible even when used outdoors. FIG. 4 is a configuration diagram of an embodiment of the correlation tracking device according to the present invention. In FIG. After the supplied video signal is passed through the analog-to-digital conversion circuit 7 and converted into a digital signal using alpha bits, the area dividing circuit 8 extracts a horizontally correlated screen and a vertically uncorrelated screen from the entire screen. The average value is detected for each screen using the average value detection circuits 9H and 9V.Next, from the video signal divided by the area division circuit 8 in the same way for the input video, 1 The average value obtained for the previous video is subtracted using subtraction circuits 10H and 10V.Next, from the video with the DC component removed, switch 11
A reference screen is cut out in advance using H and 11V and stored in the memory 12H and 12V. The video signal of the correlation screen is input to horizontal and vertical correlators 13H and 13V, and a correlation coefficient is calculated. The calculated correlation coefficient is sent to the maximum value detection circuit 1.
The image pickup device A desired target or scene within the field of view of 6 can be tracked with an electronic loop. Further, the tracking coordinate signal output circuit 15 can be used to output an error signal to the servo mount 5 to control the attitude of the imaging device 6, so that a desired target or scene can be kept stationary on the screen and tracked. Although the above description has been made of a cross-shaped case in which a correlated screen and a reference screen are set in each horizontal and vertical direction and correlation calculations are performed independently of each other in order to perform real-time processing, the present invention is not limited to this. It can also be used when the entire screen is used as a correlated screen and one rectangular area is used as a reference screen, and this is scanned two-dimensionally to calculate a correlation coefficient and perform tracking. As described above, in the correlation tracking device according to the present invention, the average value of the video signal of the correlated screen is determined in each horizontal and vertical direction, and only the AC component is extracted by subtracting this average value from the video signal. Since the correlation coefficient is calculated using the video signal of the reference screen cut out from the correlated screen and a part of it and stored in memory in advance, the SNR of the correlation coefficient decreases due to the DC component of the video signal and This has the advantage of being able to accurately and stably track a desired target or scene within the field of view of the imaging device, since fluctuations in SNR due to DC component fluctuations depending on brightness can be removed.

[Brief explanation of the drawing]

Figure 1 is a layout diagram of each screen when a cross-shaped correlated screen and reference screen are used, Figure 2 is an enlarged view of the horizontal correlated screen and reference screen, and Figure 3 is a conventional correlation tracking device. FIG. 4 is a diagram illustrating a comparison of the correlation coefficients obtained by the correlation tracking device according to the present invention, and FIG. 4 is a configuration diagram of an embodiment of the correlation tracking device according to the present invention. In the figure, 1 is a horizontal correlated screen, 2 is a vertical correlated screen, 3 is a horizontal reference screen, 4 is a vertical reference screen, 5 is a servo mount, 6 is an imaging device, 7 is an analog-digital conversion circuit, and 8 is an area Split circuit, 9H, 9V
is a horizontal/vertical average value detection circuit, 10H, 10V is a horizontal/vertical subtraction circuit, 11H, 11V is a horizontal/vertical switch, 12H, 11V is a horizontal/vertical memory,
13H, 13V are horizontal/vertical correlators, 14H, 1
4V is a horizontal/vertical maximum value detection circuit, and 15 is a tracking coordinate signal detection circuit. It should be noted that the same or corresponding parts in the figures are indicated by the same reference numerals.

Claims (1)

[Claims] 1. Calculate the correlation coefficient between the analog-to-digital converted screen of the video signal supplied from the imaging device and the reference screen stored in advance, detect the maximum correlation point, and locate the desired target or target within the field of view of the imaging device. In a correlation tracking device that tracks a scene, a correlated screen is extracted from the entire screen, the average value of the video signal of the entire correlated screen is determined, and only the AC component is extracted by subtracting this average value from the original video signal. The correlation coefficient is obtained by using the extracted video signal of the correlated screen and the video signal of a reference screen cut out from a part of the correlated screen and stored in advance. Tracking device.