Miniature camera detection method based on cat eye effect dynamic characteristics

Abstract

The invention discloses a miniature camera detection method based on cat eye effect dynamic characteristics, and the method comprises the following steps: S1, placing a detection light emitter and a collection camera at a preset distance in front of a to-be-detected region, and starting detection light to irradiate the to-be-detected region; s2, the detection light emitter and the acquisition camera are moved in a translational scanning mode, echo signals reflected by a target in the to-be-detected area are received, and echo light spots are generated on the display device; s3, tracking a motion track range of the echo light spot on a display device, and calculating a field angle of a corresponding target based on the track range; s4, comparing the field angle obtained by calculation with a preset field angle threshold value of the micro camera, and judging whether the target is the micro camera or not; the micro camera in the to-be-detected area is detected by analyzing the static characteristics of the echo light spots and the motion trail of the echo light spots generated by plain scanning, and the method has the advantage of being high in detection accuracy.

Description

Technical Field

[0001] The present invention relates to the field of detection technology, and in particular to a micro-camera detection method based on the dynamic characteristics of the cat's eye effect. Background Art

[0002] With the development of science and technology, various monitoring equipment such as micro cameras and pinhole cameras are constantly updated and enter people's daily lives, posing a serious threat to the privacy of people's indoor activities. Now there are many detectors on the market to check whether there are cameras indoors, including voice control detection, infrared detection, and active detection of detection light. Most of the active detectors for detection light are designed based on the "cat's eye effect". The "cat's eye effect" refers to the use of strong detection light to illuminate the photoelectric device. Due to the structural characteristics of the photoelectric device, it will generate back-reflected light pointing in the direction of the detection light, and the echo energy is 2-4 orders of magnitude stronger than that of the diffuse reflection target. By utilizing this feature, the specific position of the cat's eye target can be determined by observing the echo signal characteristics of the cat's eye target; however, due to the complex indoor environment, the cat's eye effect echo signal will be affected by background stray light and atmospheric factors, making it particularly difficult to find the cat's eye target. Currently known static features include area size, morphological characteristics and grayscale distribution. Usually, the cat's eye echo spot of a micro camera is circular, but there are many objects with circular reflected light indoors to interfere with the detector's judgment, and because the image noise is almost the same as the grayscale distribution of the cat's eye effect echo spot, target recognition cannot be performed. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for detecting micro cameras based on the dynamic characteristics of the cat's eye effect. By analyzing the static characteristics of the echo spot and the motion trajectory of the echo spot generated by the flat scan, the present invention detects micro cameras within the test area, achieving high detection accuracy.

[0004] The technical solution of the present invention is a micro-camera detection method based on the dynamic characteristics of the cat's eye effect, which is carried out in the following steps:

[0005] Step S1: placing the detection light emitter and the acquisition camera at a preset distance in front of the area to be measured, and turning on the detection light to illuminate the area to be measured;

[0006] Step S2: moving the detection light emitter and the acquisition camera in a translational scanning manner to receive the echo signal reflected by the target in the test area and generate an echo spot on the display device;

[0007] Step S3: Tracking the motion trajectory of the echo spot on the display device, and calculating the field of view angle of the corresponding target based on the trajectory range;

[0008] Step S4: Compare the calculated field of view angle with the preset field of view angle threshold of the micro camera to determine whether the target is a micro camera.

[0009] In the above-mentioned method for detecting a micro camera based on the dynamic characteristics of the cat's eye effect, the formula for the ratio calculation is as follows:

[0010]

[0011] In the formula, α is the field of view angle of the target in the area to be measured, S is the field of view width of the target in the area to be measured, and d is the distance between the acquisition camera and the area to be measured;

[0012] The calculation of the field of view width S is shown in the following formula: [[ID=z13]]

[0013]

[0014] In the formula, L is the field of view width of the acquisition camera, N is the line width of the reflected light spot movement trajectory on the display area of the display device, M is the line width of the display area of the display device, H is the spot diameter of the detection light of the detection light emitter in the detection area, and Y is the line width of the detection light on the display area of the display device;

[0015] The calculation of the field of view width L of the acquisition camera is shown in the following formula:

[0016]

[0017] In the formula, β is the field of view angle of the acquisition camera;

[0018] The calculation of the spot diameter H of the detection light of the detection light emitter in the detection area is shown in the following formula:

[0019]

[0020] In the formula, γ is the divergence angle of the detection light of the detection light emitter.

[0021] In the above-mentioned method for detecting a micro camera based on the dynamic characteristics of the cat's eye effect, when the field of view angle β of the acquisition camera is less than or equal to the divergence angle γ of the detection light of the detection light emitter, the relationship between the field of view angle α of the target in the area to be measured and the field of view angle β of the acquisition camera is shown in the following formula:

[0022]

[0023] In the above-mentioned method for detecting a micro camera based on the dynamic characteristics of the cat's eye effect, when the field of view angle β of the acquisition camera is less than or equal to the divergence angle γ of the detection light of the detection light emitter and the field of view angle β of the acquisition camera is greater than or equal to the field of view angle α of the target in the area to be measured, the relationship between the divergence angle γ of the detection light of the detection light emitter and the field of view angle α of the target in the area to be measured is shown in the following formula:

[0024]

[0025] In the aforementioned method for detecting a micro camera based on the dynamic characteristics of the cat's eye effect, the acquisition camera adjusts the field of view angle by switching lenses with different magnification factors. The smaller the magnification factor, the larger the field of view angle, and the larger the magnification factor, the smaller the field of view angle.

[0026] In the aforementioned method for detecting a micro camera based on the dynamic characteristics of the cat's eye effect, before step S2, screening of the target in the area to be measured is performed based on the static characteristics of the reflected light spot.

[0027] In the aforementioned method for detecting a micro camera based on the dynamic characteristics of the cat's eye effect, the static characteristics include the size and area of the reflected light spot, the morphological characteristics, and the gray-scale distribution.

[0028] In the aforementioned method for detecting a micro camera based on the dynamic characteristics of the cat's eye effect, in step S4, if the calculated field of view angle is greater than or equal to the minimum threshold of the field of view angle of the micro camera, the target is determined to be a micro camera.

[0029] Compared with the prior art, in the present invention, the detection light emitter is translated to irradiate the target in the area to be measured, the detection light emitter and the acquisition camera are moved by a translational scanning method, the echo signal reflected by the target in the area to be measured is received and a reflected light spot is generated on the display device, the movement trajectory range of the reflected light spot on the display device is traced, the field of view angle of the target corresponding to the movement trajectory of the reflected light spot is calculated by proportional calculation using the field of view angle of the acquisition camera, the divergence angle of the detection light of the detection light emitter, the line width of the display area of the display device, and the line width of the movement trajectory, and the calculated field of view angle is compared with the preset threshold of the field of view angle of the micro camera to determine whether the target is a micro camera; the translational scanning method for receiving the trajectory of the reflected light spot is used for calculating the field of view angle, and the large field of view angle is used as a characteristic of the micro camera to distinguish it from other highly reflective targets, so that reliable detection of the micro camera can be performed based on this characteristic. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a flow schematic diagram of the present invention;

[0031] Figure 2 is a diagram of the translational detection process when the field of view angle of the target in the area to be measured is smaller than the divergence angle of the detection light and the divergence angle of the detection light is smaller than the field of view angle of the acquisition camera;

[0032] Figure 3 is a diagram of the bright spot trajectory when the field of view angle of the target in the area to be measured is smaller than the divergence angle of the detection light and the divergence angle of the detection light is smaller than the field of view angle of the acquisition camera;

[0033] Figure 4It is a translation detection process diagram when the divergence angle of the detection light is close to or smaller than the field of view angle of the acquisition camera and the divergence angle of the detection light is smaller than the field of view angle of the target in the area to be measured;

[0034] Figure 5 It is a bright spot trajectory diagram when the divergence angle of the detection light is close to or smaller than the field of view angle of the acquisition camera and the divergence angle of the detection light is smaller than the field of view angle of the target in the area to be measured;

[0035] Figure 6 It is a translation detection process diagram when the field of view angle of the target in the area to be measured is smaller than the field of view angle of the acquisition camera and the field of view angle of the target in the area to be measured is larger than the divergence angle of the detection light;

[0036] Figure 7 It is a bright spot trajectory diagram when the field of view angle of the target in the area to be measured is smaller than the field of view angle of the acquisition camera and the field of view angle of the target in the area to be measured is larger than the divergence angle of the detection light;

[0037] Figure 8 It is a translation detection process diagram when the divergence angle of the detection light is similar to the field of view angle of the acquisition camera and the field of view angle of the acquisition camera is larger than the field of view angle of the target in the area to be measured;

[0038] Figure 9 It is a bright spot trajectory diagram when the divergence angle of the detection light is similar to the field of view angle of the acquisition camera and the field of view angle of the acquisition camera is larger than the field of view angle of the target in the area to be measured;

[0039] Figure 10 It is a three-dimensional internal structure diagram of the acquisition camera of the present invention;

[0040] Figure 11 It is a plan view of the internal structure of the acquisition camera of the present invention;

[0041] Figure 12 It is a schematic diagram of the translation detection of the present invention;

[0042] Figure 13 It is a diagram of the initial position and disappearance position of the reflected light spot when performing translation detection at a distance of 30 cm from the area to be scanned and using a lens with a magnification of ×0.6 for the acquisition camera in the embodiment;

[0043] Figure 14 It is a diagram of the initial position and disappearance position of the reflected light spot when performing translation detection at a distance of 50 cm from the area to be scanned and using a lens with a magnification of ×0.6 for the acquisition camera in the embodiment;

[0044] Figure 15 It is a diagram of the initial position and disappearance position of the reflected light spot when performing translation detection at a distance of 50 cm from the area to be scanned and using a lens with a magnification of ×3.0 for the acquisition camera in the embodiment. Detailed implementation manners

[0045] The present invention will be further described below in conjunction with the accompanying drawings and embodiments, but it shall not be used as a basis for limiting the present invention.

[0046] Embodiment: A method for detecting a micro camera based on the dynamic characteristics of the cat's eye effect, as shown in the attached Figure 1 figure, and is carried out according to the following steps:

[0047] Step S1: Place the detection light emitter (laser emitter) and the acquisition camera fixed in the same position and in the same direction at a preset distance in front of the area to be measured, turn on the detection light to irradiate the area to be measured. After the detection light irradiates a high-reflectivity target, an echo light spot stronger than the background light will be generated. The acquisition camera receives the echo signal of the area to be measured and displays the echo light spot on the display device. Exclude the target in the area to be measured corresponding to the non-conforming echo light spot by analyzing static characteristics including size area, morphological features, and gray-scale distribution;

[0048] Step S2: Mark the serial numbers for the targets corresponding to the echo light spots excluded by the static characteristics; as shown in the attached Figure 12 figure, the remaining targets in the area to be measured are scanned and irradiated by the translational movement of the detection light emitter. Since the structure of the micro camera includes a lens group, an echo light spot will be generated. At the same time, the micro camera has a certain field of view range, so its echo light spot can be received within a certain range;

[0049] Step S3: Track the range of the movement trajectory formed by the target echo light spot, display the movement trajectory of the echo light spot on the display device, and calculate the field of view angle of the corresponding target based on the trajectory range;

[0050] First, calculate the field of view width L of the acquisition camera and the diameter H of the light spot generated by the detection light in the area to be measured:

[0051]

[0052] Then, according to the pattern on the display device, obtain the line width Y of the detection light on the display area, and calculate the field of view width S and field of view angle α of the target in the area to be measured through the proportional relationship:

[0053]

[0054] In the formula, L is the field of view width of the acquisition camera, N is the line width of the movement trajectory of the echo light spot on the display area of the display device, M is the line width of the display area of the display device, and H is the diameter of the light spot of the detection light of the detection light emitter in the detection area.

[0055] For the dynamic monitoring method, due to the different divergence angles of the detection light, the field of view angles of the acquisition camera and the target in the area to be measured, the range of the observed target movement trajectory on the display device is also different. According to the relationship between their field of view angles, the following situations can be divided:

[0056] (1) When the target field of view angle of the area to be measured is smaller than the divergence angle of the detection light, and the divergence angle of the detection light is smaller than the field of view angle of the acquisition camera, as shown in Appendices Figure 2 (a)-(f), translational scanning is performed, and the trajectory of the bright spot traced on the display device is as shown in Appendices Figure 3 . The circular aperture represents the light spot irradiated by the detection light, the marked red dot represents the position where the micro camera is located when detected, and the dashed line represents the movement trajectory of the traced backlight spot; according to the cat-eye effect, only under strong light irradiation can the micro camera have a strong echo signal received, so in Appendices Figure 3 , the movement trajectory of the backlight spot can only be observed within the circular aperture. Through the movement trajectory, the relationship between the field of view angle α of the target in the area to be measured and the field of view angle β of the acquisition camera is shown in the following formula:

[0057]

[0058] (2) When the divergence angle of the detection light is close to or smaller than the field of view angle of the acquisition camera, and the size of the divergence angle of the detection light is smaller than the field of view angle of the target in the area to be measured, as shown in Appendices Figure 4 (a)-(d), translational scanning is performed, and the trajectory of the bright spot traced on the display device is as shown in Appendices Figure 5 . In this case, it is not convenient to calculate the field of view angle of the cat-eye target, but the plane interference target with high reflectivity can be excluded by the dynamic detection method.

[0059] (3) When the field of view angle of the target in the area to be measured is smaller than the field of view angle of the acquisition camera, and the field of view angle of the target in the area to be measured is larger than the divergence angle of the detection light, as shown in Figure 6 (a)-(f), translational scanning is performed, and the trajectory of the bright spot traced on the display device is as shown in Appendices Figure 7 . Within the range irradiated by the detection light, the movement trajectory of the backlight spot of the cat-eye target can be observed on the display device, but in the processes a to c and d to f in Appendices Figure 6 , the target in the area to be measured has appeared on the display device, but due to the lack of irradiation of the detection light, no backlight spot can be generated.

[0060] (4) When the divergence angle of the detection light is greater than or close to the field of view angle of the acquisition camera, and the field of view angle of the acquisition camera is greater than or equal to the field of view angle of the target in the area to be measured, the translational irradiation scanning process is as shown in Appendices Figure 8 (a)-(d), and the traced bright spot trajectory is as shown in Appendices Figure 9 . The backlight spot of the target in the area to be measured can move within the display device to form a movement trajectory, and then its line width can be obtained. The relationship between the divergence angle γ of the detection light of the detection light emitter and the field of view angle α of the target in the area to be measured is shown in the following formula:

[0061]

[0062] As can be seen from the above situation, the field of view width of the acquisition camera is related to the distance between the acquisition camera and the target in the area to be measured. If the distance is too small, the observable area will also decrease accordingly. By increasing the distance between the two, the field of view width of the acquisition camera can be increased, that is, a larger range can be observed on the display device.

[0063] For the acquisition device, the scanning efficiency can be improved by increasing the area covered by the detection light and the field of view of the acquisition camera; in the establishment of the dynamic detection physical model, it can be known that the field of view size is changed by adjusting the field of view angle, and the adjustment of the field of view angle is related to the magnification of the acquisition camera. The field of view width is changed by adjusting the focal length of the optical center element of the acquisition camera. As shown in the attached Figure 10 and the attached Figure 11 As shown, according to the pixel size that the acquisition camera can receive, lenses with different focal lengths are replaced. Figure 9 In , the pixel size received by the acquisition camera is M×N, the corresponding field of view range is P×Q, the focal length of the lens is f, and the straight-line distance between the lens and the area to be measured is d. According to the Pythagorean theorem, the radius of the circle formed by the four vertices of the acquisition camera is calculated:

[0064]

[0065] Construct a sphere with the focus of the lens as the center of the sphere and a radius The projected area of the acquisition camera projected onto the sphere is calculated as:

[0066]

[0067] Finally, the solid angle Ω of the field of view can be obtained as:

[0068]

[0069] According to the above formula, it can be obtained that by replacing the lens with a larger focal length f, the solid angle of the acquisition camera can be increased. That is, when the straight-line distance between the lens and the area to be measured remains unchanged, different lenses with different focal lengths can be replaced to increase the observable field of view area; using lenses with different magnifications can achieve the effect of regulating the field of view angle. The smaller the magnification, the shorter the focal length, and the larger the field of view angle. At the same distance, the observable range is larger; conversely, the smaller the field of view angle, the smaller the observable range.

[0070] Step S5: Compare the field of view angle obtained in step S4 with the field of view angle range corresponding to the micro camera. The target corresponding to the field of view angle greater than or equal to the minimum threshold of the field of view angle range is the micro camera.

[0071] Based on the above steps, three lenses with different magnifications are used, namely ×0.6, ×1.0, and ×3.0, and the corresponding focal lengths are 15 mm, 23 mm, and 70 mm respectively. The divergence angle of the detection light emitted by the detection light emitter is 61.92°, and the field of view angle of the simulated micro camera is 57.96°.

[0072] As shown in Figure 13 (a)-(b), the acquisition camera uses a lens with a magnification of ×0.6. The distance between the detection light emitter and the acquisition camera and the area to be measured is 30 cm. The starting and ending positions of the traced backlight spot are as Figure 14 shown, and it conforms to the fact that the field of view angle of the micro camera is less than the divergence angle of the detection light, and the divergence angle of the detection light is less than the field of view angle of the acquisition camera. According to Figure 14 , the pixel distance N that the backlight spot moves on the display device can be calculated to be 677. The diameter Y of the red light emitted by the detection light emitter displayed on the screen is 749 pixels. By calculation, the divergence angle of the red light is 61.92°, and the field of view angle of the target in the area to be measured is 56.95°, which is relatively close to the theoretical value of 57.96°. It can be judged that this backlight spot is a simulated micro camera.

[0073] As shown in Figure 14 (a)-(b), the detection light emitter and the acquisition camera are moved to a position 50 cm away from the area to be measured, and a lens with a magnification of ×0.6 is selected for translational scanning. As Figure 15 shown, the pixel distance N that the spot moves on the display device is 597. The diameter Y of the red light emitted by the detection light emitter displayed on the display device is 643 pixels. By calculation, the field of view angle of the target in the area to be measured is 58.24°, which is relatively close to the theoretical value of 57.96°. It can be judged that this backlight spot is a simulated micro camera.

[0074] As shown in Figure 15 (a)-(b), keeping the distance from the area to be scanned at 50 cm, a lens with a magnification of ×3.0 is selected for translational scanning. The field of view angle of the acquisition camera is 22.62°, and the divergence angle of the detection light is 61.92°, which conforms to the fact that the divergence angle of the detection light is close to or smaller than the field of view angle of the acquisition camera, and the field of view angle of the CCD camera is less than the field of view angle of the peeping device. As shown in Figure 15 , the backlight spot always appears on the display device.

[0075] In summary, the proposed micro-camera detection method based on the dynamic characteristics of the cat's eye effect can accurately calculate the field of view angle of the target in the detection area under different distances between the acquisition camera and the detection area, and under different acquisition camera lens magnifications. This calculation is then compared with the theoretical field of view angle of the micro-camera, effectively identifying the simulated micro-camera. By analyzing the static characteristics of the echo spot, interfering targets are initially eliminated, reducing the workload of subsequent detection. The motion trajectory of the echo spot is acquired by the translational scanning of the detection light emitter and the acquisition camera, and the field of view angle is calculated based on relevant parameters. This dynamic feature-based detection method fully considers the detection conditions under different field of view relationships, effectively avoiding interference from factors such as background stray light, atmospheric factors, and other highly reflective circular objects indoors, significantly improving the accuracy and reliability of micro-camera detection. The method is relatively simple to operate and can flexibly adapt to different detection scenarios by adjusting parameters such as the acquisition camera lens magnification and distance from the detection area. It has promising application prospects in protecting the privacy of people's indoor activities and preventing illegal micro-camera photography, and is expected to provide an efficient and practical technical means for security detection in related fields.

Claims

1. A detection method for a micro camera based on the dynamic characteristics of the cat's eye effect, characterized in that: Proceed as follows: Step S1: Place the detection light emitter and the acquisition camera at a preset distance in front of the area to be measured, and turn on the detection light to irradiate the area to be measured; Step S2: Move the detection light emitter and the acquisition camera by translational scanning, receive the echo signal reflected by the target in the area to be measured, and generate an echo light spot on the display device; Step S3: Track the movement trajectory range of the echo light spot on the display device, and calculate the field of view angle of the corresponding target based on the trajectory range; Step S4: Compare the calculated field of view angle with the preset field of view angle threshold of the micro camera to determine whether the target is a micro camera.

2. The method for detecting a micro camera based on the dynamic characteristics of the cat's eye effect according to claim 1, wherein: The formula for the ratio calculation is as follows: In the formula, α is the field of view angle of the target in the area to be measured, S is the field of view width of the target in the area to be measured, and d is the distance between the acquisition camera and the area to be measured; The calculation of the field of view width S is shown in the following formula: In the formula, L is the field of view width of the acquisition camera, N is the line width of the movement trajectory of the echo light spot on the display area of the display device, M is the line width of the display area of the display device, H is the spot diameter of the detection light of the detection light emitter in the detection area, and Y is the line width of the detection light on the display area of the display device; The calculation of the field of view width L of the acquisition camera is shown in the following formula: In the formula, β is the field of view angle of the acquisition camera; The calculation of the spot diameter H of the detection light of the detection light emitter in the detection area is shown in the following formula: In the formula, γ is the divergence angle of the detection light of the detection light emitter.

3. The method for detecting a micro camera based on the dynamic characteristics of the cat's eye effect according to claim 2, characterized in that: When the field of view angle β of the acquisition camera is less than or equal to the divergence angle γ of the detection light of the detection light emitter, the relationship between the field of view angle α of the target in the area to be measured and the field of view angle β of the acquisition camera is shown in the following formula:

4. The micro camera detection method based on the dynamic characteristics of the cat's eye effect according to claim 2, wherein: When the field of view angle β of the acquisition camera is less than or equal to the divergence angle γ of the detection light of the detection light emitter and the field of view angle β of the acquisition camera is greater than or equal to the field of view angle α of the target in the area to be measured, the relationship between the divergence angle γ of the detection light of the detection light emitter and the field of view angle α of the target in the area to be measured is shown in the following formula:

5. The micro-camera detection method based on the dynamic characteristics of the cat's eye effect according to claim 1, wherein: The acquisition camera adjusts the field of view angle by switching lenses with different magnification factors. The smaller the magnification factor, the larger the field of view angle, and the larger the magnification factor, the smaller the field of view angle.

6. The method for detecting a micro camera based on the dynamic characteristics of the cat's eye effect according to claim 1, characterized in that: Before Step S2, it includes screening the target in the area to be measured based on the static characteristics of the echo light spot.

7. The method for detecting a micro camera based on the dynamic characteristics of the cat's eye effect according to claim 6, characterized in that: The static characteristics include the size area, morphological characteristics, and gray-scale distribution of the echo light spot.

8. The method for detecting a micro camera based on the dynamic characteristics of the cat's eye effect according to claim 1, wherein: In Step S4, if the calculated field of view angle is greater than or equal to the minimum threshold of the field of view angle of the micro camera, it is determined that the target is a micro camera.

Images