CN102098442B - Method and system for calibrating misalignment degree between optical axis and visual axis of zoom camera - Google Patents

Abstract

The invention discloses a method and system for calibrating the non-overlap ratio of an optical axis and a visual axis of a zoom camera, belonging to the technical field of television cameras, which solve the difficult problems that the non-overlap ratio of the optical axis and the visual axis of the zoom camera is not convenient to adjust manually by the existing mechanical method, and even can not be debugged on site. In the invention, the non-overlap ratio of the two axes is measured by a digital image processing method; and a start point of an image matrix is movably output at two directions of line and field in outputting to compensate the non-overlap ratio, so as to lead that the visual axis is overlapped with the optical axis. The method and system provided by the invention have the advantages of small volume, high reliability and the like, are simple and rapid in debugging, require no moving components, are especially suitable for the fields of aviation, spaceflight and military, have high requirements on the overlap ratio of the optical axis and the visual axis, have poor use environments, are not convenient or do not allow mechanical adjustment on site.

Description

Method and system for calibrating misalignment degree between optical axis and visual axis of zoom camera

technical field

The invention belongs to the technical field of television cameras, and in particular relates to a method and system for calibrating the misalignment degree of the optical axis and visual axis of a zoom camera.

Background technique

The TV camera is mainly composed of an optical lens and an area array photoelectric sensor. According to whether the focal length of the optical lens is variable, it is divided into a fixed-focus lens and a zoom lens. The zoom lens can change the size of the field of view. When the focal length is short, the field of view is large, and the observation range is also large, which is conducive to finding and capturing the target; when the focal length is long, the field of view is small, suitable for observing the details of the target or distant targets . Due to the above advantages of the zoom lens, TV cameras using the zoom lens are widely used in the fields of aviation, aerospace, weapons, etc., for measuring, tracking and locating long-distance targets.

The optical axis of the zoom lens refers to the centerline of the lens optical system from telephoto to short focal length; correspondingly, the line passing through the center of the output image of the image sensor and perpendicular to the target surface of the image sensor is defined as the visual axis. Under normal circumstances, when the TV camera is assembled, the misalignment between the optical axis and the visual axis must be less than the specified value, so as to ensure that the scene in the center of the image does not deviate greatly during the zooming process.

According to the principle of geometric optics, as shown in Figure 1, if the deviation between the optical axis and the visual axis on the target surface is Δ when the short focal length is measured, then the deviation is nΔ. And if Δ=0 when the focal length is short, then the deviation nΔ=0 of the telephoto position. For photoelectric measurement and control instruments, fire control systems, and spacecraft docking systems that require high positioning accuracy, the misalignment index between the optical axis and the visual axis is very important.

However, due to factors such as time, environment, and structural materials, the precisely calibrated optical axis and visual axis will have a large or small deviation after a period of time at the factory. In severe cases, it will affect the normal use of the equipment. Perform a recalibration. In the past, the calibration of the optical axis and the optical axis was done mechanically. It was necessary to open the casing of the camera and manually try and retry until the optical axis and the optical axis were adjusted to the allowable range of accuracy. At the equipment site, this debugging method is cumbersome, and the accuracy is difficult to guarantee. Due to the need for mechanical disassembly, debugging and reinstallation, it is easy to cause accidental damage to the equipment, and has a great impact on the protective performance of the equipment shell, such as watertight and airtight. Optoelectronic devices cannot even be calibrated mechanically.

Contents of the invention

In order to solve the problem that it is difficult to calibrate the misalignment of optical axis and visual axis by using conventional mechanical methods in the prior art, the present invention provides a method and system for calibrating the misalignment of optical axis and visual axis of a zoom camera.

The technical solution adopted by the present invention to solve technical problems is as follows:

The method for calibrating the degree of misalignment between the optical axis and the visual axis of a zoom camera includes the following steps:

The first step, connect the output terminal of the camera to be calibrated with the adjustment circuit, connect the output of the adjustment circuit with the TV monitor, adjust the position of the camera and the distant target, so that the TV monitor can see the target image acquired by the camera;

In the second step, when the zoom lens of the camera is adjusted to a long focal length, align the visual axis of the camera with the centroid of the distant target, calculate the distance between the target centroid and the visual axis by adjusting the circuit, and superimpose it on the image through the TV The monitor is displayed, and after alignment, the relative position of the target and the camera is fixed;

The third step is to turn the zoom lens of the camera to the short focal length end, and calculate the deviation Δ between the target centroid and the visual axis by adjusting the circuit, which is the degree of misalignment between the optical axis and the visual axis, and store it in non-volatile RAM the deviation Δ;

The fourth step, the adjustment circuit decodes the video image signal from the image sensor of the camera into a digital video stream with a fixed frame format through the video decoder;

The fifth step, the adjustment circuit reads the digital image signal input by the video decoder through the digital image processor and stores it in the image memory in a fixed format sequentially from left to right and from top to bottom;

The sixth step, the adjustment circuit reads the deviation Δ stored in the third step from the non-volatile RAM through the digital image processor, corrects the starting point of the image output according to the deviation Δ, and then from the starting point in order from the image memory The read image data is sent to the video encoder, and finally the video encoder outputs a video image that has been calibrated with the optical axis and the boresight axis.

The optical axis and visual axis misalignment calibration system of the zoom camera includes an adjustment circuit and a TV monitor, the adjustment circuit is connected with the image sensor of the camera to be calibrated, and the adjustment circuit automatically performs real-time calibration processing on the video signal output by the image sensor ; The TV monitor is connected with the adjustment circuit to display the target image obtained by the camera calibrated by the adjustment circuit.

Above-mentioned adjusting circuit comprises video decoder, digital image processor, image memory, non-volatile type RAM and video coder, and described digital image processor is connected with video decoder, image memory, non-volatile type RAM, video coder respectively Connect; the video decoder decodes the video image signal sent by the image sensor of the camera into a digital video stream in a fixed frame format, and the digital image processor reads in the digital image signal input by the video decoder and presses from left to Right, from top to bottom, sequentially stored in the image memory in a fixed format; the non-volatile RAM stores the degree of misalignment between the optical axis and the visual axis; the digital image processor corrects the image according to the degree of misalignment between the optical axis and the visual axis The starting point of the output, and read the image data from the image memory sequentially from the starting point to send to the video encoder, and finally the video encoder outputs the video image that has completed the calibration of the optical axis and the visual axis.

The beneficial effects of the present invention are: no disassembly of the equipment is performed at the scene of using the TV camera, and the high-precision automatic calibration of the optical axis and the visual axis is completely completed by the circuit; it has the advantages of small size, simple and fast debugging, no moving parts, high reliability, and Outstanding advantages such as no damage to the equipment casing; especially suitable for aviation, aerospace and military fields that require high coincidence between the optical axis and the visual axis, and where the environment is harsh but it is inconvenient or not allowed to perform mechanical adjustments on site, such as airtight and outer space, etc. .

Description of drawings

Fig. 1 is a schematic diagram of misalignment of optical axis and visual axis in the prior art.

Fig. 2 is a structural block diagram of the system for calibrating the misalignment degree between the optical axis and the visual axis of the zoom camera of the present invention.

Fig. 3 is a structural block diagram of the adjustment circuit in the present invention.

Fig. 4 is a schematic diagram of an m×n pixel matrix in the present invention.

Fig. 5 is a schematic diagram of a pixel matrix in which the center of the image in Fig. 4 is moved to point E.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

The adjustment process of the optical axis and visual axis misalignment calibration system of the zoom camera of the present invention is divided into two steps: misalignment detection and misalignment calibration:

Check the degree of misalignment: put the zoom lens of the camera at the longest focus position, align the center of the image with the centroid of a circular or cross-shaped target at infinity, and the image signal is transmitted from the image sensor to the adjustment circuit; Then, keeping the current position of the camera unchanged, adjust the zoom lens to the shortest focus position, and the calculated coordinate difference at this time is the misalignment deviation Δ between the optical axis and the visual axis.

Calibration of misalignment: This step is mainly completed by the adjustment circuit. The composition and structure of the adjustment circuit is shown in Figure 3. Its working principle is: the video image signal transmitted from the image sensor to the adjustment circuit is first decoded into a digital video stream with a fixed frame format by the video decoder in the adjustment circuit, and the digital image processor reads the digital image signal input by the video decoder. and stored in the image memory in a fixed format in order from left to right and from top to bottom, so that each frame of image forms an m×n pixel matrix in the image memory, as shown in Figure 4. Each of its pixels has a one-to-one corresponding position in the image. Here m is the number of columns of the matrix and n is the number of rows. The first row of pixels in the image is: (0, 0) (0, 1) (0, 2)...(0, m). The first column of pixels is: (1,0)(1,0)(2,0)...(n,0). If the entire frame image is to be output, the digital image processor will follow the order of input: (0,0)-(0,1)...(0,m)-(1,0).. ....(n, m) read the image data from the image memory, and then output it to the video encoder, and the video encoder decodes and outputs it according to the format of the original video signal. At this time, the same image as the output of the image sensor can be seen on the TV monitor. The coordinates of ★ in Figure 4 are is the center of the image. Normally, this point is the intersection of the boresight and the target surface of the image sensor. In Figure 4, E is the intersection coordinate of the optical axis and the target surface of the image sensor as

的画面。依此，我们可以如图5所示通过改变输出图像的起始点的方法将图4中的图像中心由★移到E点。图5中读取图像的起始点为(1，-1)，则由粗框包围的区域为光轴与视轴不重合度校正后的图像输出区域。这样，由调整电路输出的视频图像就是光轴与视轴重合的了，实现了对光轴和视轴不重合度的校准。图5中的“+”是为了使输出满足图像帧格式要求而在图像矩阵中添加的像元，它们的值没有特殊要求，但为使图像边缘无明显突变，一般取其相邻实际所采集像素的值。If the starting point when the adjustment circuit outputs the image does not start from (0, 0) but from (1, 0), the image output by the adjustment circuit is compared with the image directly output by the image sensor on the screen of the TV monitor. appears to be shifted to the left

screen. Accordingly, we can move the center of the image in Figure 4 from ★ to point E by changing the starting point of the output image as shown in Figure 5. The starting point of reading the image in Fig. 5 is (1, -1), then the area surrounded by the thick frame is the image output area after the misalignment between the optical axis and the visual axis is corrected. In this way, the optical axis of the video image output by the adjustment circuit coincides with the visual axis, and the calibration of the misalignment of the optical axis and the visual axis is realized. The "+" in Figure 5 is the pixel added to the image matrix in order to make the output meet the requirements of the image frame format. There is no special requirement for their values, but in order to make the edge of the image have no obvious mutation, it is generally taken as the adjacent actual collected The value of the pixel.

In actual work, every time the digital image processor in the adjustment circuit outputs an image, it reads the previously stored deviation Δ from the non-volatile RAM, and corrects the starting point of the image output; then sequentially reads from the starting point The image data is taken and sent to the video encoder, and finally the video encoder outputs a video image that has been calibrated with the optical axis and the boresight axis. As shown in Figure 1, at this time, due to the deviation Δ=0 between the optical axis and the visual axis, when the optical lens changes between long focus and short focus, the target centroid located in the center of the image is in the image at both long focus and short focus positions center.

Specific examples:

The target in Figure 2 is a target at infinity, which can be realized by using a collimator indoors, and it can be a long-distance point target such as a celestial body, a ground target, etc. due to limited conditions in the field.

The specific implementation steps are as follows:

1) Connect the TV camera that needs to be calibrated according to Figure 2 to ensure that the image can be seen through the TV monitor;

2) When the camera is at the long focal length of the zoom lens, the visual axis is aligned with the centroid of the distant target. At this time, the adjustment circuit calculates the distance between the target centroid and the visual axis and superimposes it on the image and displays it on the TV monitor , for the reference of the debugger, the unit of the number generally displayed is pixel; after alignment, the relative position of the target and the TV camera is fixed;

3) Turn the zoom lens to the short focal length end. At this time, the difference between the target centroid and the visual axis calculated by the adjustment circuit is the degree of misalignment between the optical axis and the visual axis; it is stored in the digital image processor in the adjustment circuit. In the non-volatile RAM, it is ready to call when used, so that the non-coincidence test is completed;

4) After calibration, when the zoom TV camera is working normally, the video signal output by the image sensor enters the adjustment circuit; the adjustment circuit automatically performs real-time calibration processing, and then uses the same standard output as the image sensor to complete the optical axis and visual axis real-time calibration.

The model of the video decoder in Figure 3 can be TVP5150PBS, the model of the digital image processor can be TMS320DM642, the model of the image memory can be HY57V283220T, the model of the non-volatile RAM can be AM29LV033C, and the model of the second video encoder can be It is SAA7121H.

Claims (2)

1. A method for calibrating the degree of misalignment between the optical axis and the visual axis of a zoom camera, characterized in that the method comprises the following steps: The first step, connect the output terminal of the camera to be calibrated with the adjustment circuit, connect the output of the adjustment circuit with the TV monitor, adjust the position of the camera and the distant target, so that the TV monitor can see the target image acquired by the camera; In the second step, when the zoom lens of the camera is adjusted to a long focal length, align the visual axis of the camera with the centroid of the distant target, calculate the distance between the target centroid and the visual axis by adjusting the circuit, and superimpose it on the image through the TV The monitor is displayed, and after alignment, the relative position of the target and the camera is fixed; The third step is to turn the zoom lens of the camera to the short focal length end, and calculate the deviation Δ between the target centroid and the visual axis by adjusting the circuit, which is the degree of misalignment between the optical axis and the visual axis, and store it in non-volatile RAM the deviation Δ; The fourth step, the adjustment circuit decodes the video image signal from the image sensor of the camera into a digital video stream with a fixed frame format through the video decoder; The fifth step, the adjustment circuit reads the digital image signal input by the video decoder through the digital image processor and stores it in the image memory in a fixed format sequentially from left to right and from top to bottom; The sixth step, the adjustment circuit reads the deviation Δ stored in the third step from the non-volatile RAM through the digital image processor, corrects the starting point of the image output according to the deviation Δ, and then sequentially from the starting point from the image memory The read image data is sent to the video encoder, and finally the video encoder outputs a video image that has been calibrated with the optical axis and the visual axis. 2. realize the system of claim 1 described zoom camera optical axis and visual axis misalignment degree calibration method, comprise adjustment circuit and TV monitor, adjustment circuit is connected with the image sensor of the video camera that needs calibration, adjustment circuit is to described image The video signal output by the sensor automatically performs real-time calibration processing; the TV monitor is connected with the adjustment circuit to display the target image obtained by the camera calibrated by the adjustment circuit; it is characterized in that the adjustment circuit includes a video decoder, digital image processing device, image memory, non-volatile RAM and video encoder, the digital image processor is connected with video decoder, image memory, non-volatile RAM, video encoder respectively; The video image signal from the sensor is decoded into a digital video stream with a fixed frame format, and the digital image processor reads in the digital image signal input by the video decoder and converts it in a fixed format sequence from left to right and from top to bottom. Stored in the image memory; the non-volatile RAM stores the misalignment of the optical axis and the visual axis; the digital image processor corrects the starting point of the image output according to the misalignment of the optical axis and the visual axis, and sequentially from the starting point The image data is read from the image memory and sent to the video encoder, and finally the video encoder outputs a video image that has been calibrated with the optical axis and the visual axis.

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