Solar burn prevention method and device for thermal infrared imager

Abstract

The invention belongs to the technical field of infrared thermal imaging, and particularly relates to a sun burn prevention method and device for an infrared thermal imager. According to the method, solar radiation is directly judged by detecting the output data value of the detector, periodic detection is achieved, and the reliability is high. And then two strip-shaped polarized light sheets which are perpendicular to each other are vertically arranged in front of the focal plane of the detector to serve as an execution device for preventing sun burn. The position of a solar radiation focal plane is shielded from being burnt, other areas can be imaged, and the situation that scenes outside the sun are shielded and information is lost is avoided. And then compensating polarization brightness attenuation through an image brightness automatic adjustment algorithm, simulating sun imaging, and conforming to the visual habits of human eyes. According to the method disclosed by the invention, the normal imaging of the area outside the solar radiation plaque on the focal plane of the infrared detector is not influenced while the sun burn is prevented.

Description

Technical Field

[0001] The invention belongs to the technical field of infrared thermal imaging, and in particular relates to a method and device for preventing infrared thermal imagers from being sunburned. Background Art

[0002] The imaging principle of infrared thermal imagers is to use optical components to receive infrared energy radiated or reflected by objects in the scene, focus it on the focal plane of the infrared detector, and convert it into digital image signals to achieve imaging. High-temperature objects such as the sun radiate extremely strong infrared energy, which can easily cause irreversible pixel burns when focused on the focal plane of the infrared detector, forming blind pixel patches, causing local imaging function failure or performance loss of the infrared thermal imager. To avoid sunburn, people have proposed a variety of treatment methods: (1) using the closing of the shutter to cut off infrared light; (2) adding filters or filter films (sheets) to the light transmission path; (3) calculating whether the sun's position is within the field of view and using the pan / tilt steering to avoid it.

[0003] Patent CN115597720B proposes an anti-sunburn mechanism for infrared thermal imagers, which blocks light by connecting a light-blocking strip to a linear module. The width of the light-blocking strip is smaller than the width of the photosensitive window of the infrared detector. When sunlight appears in the detection scene of the infrared detector, the linear module is used to drive the light-blocking strip to translate to block the sunlight in the detection scene. At the same time, the infrared rays in the detection scene other than sunlight that are not blocked by the light-blocking strip can be collected by the infrared detector. The present invention can effectively prevent the infrared detector from being burned by sunlight, while not affecting the rest of the infrared light from irradiating the infrared detector and being able to form an image normally on the infrared focal plane, thereby realizing uninterrupted image acquisition of the observed target. Imaging in the light-blocking strip area is invalid, and scene information is lost.

[0004] Patent CN116539166A proposes an anti-burn infrared thermal imager and discloses an anti-burn infrared thermal imager. Through a filter film located on the propagation path of light, the strong light of any band in the range of 0.5μm-5.5μm is cut off, thereby effectively reducing the intensity of harmful light; at the same time, only light with a wavelength outside 0.5μm-5.5μm is allowed to pass through the filter film, thereby increasing the proportion of effective infrared light in the target. With this arrangement, it is still impossible to filter the long waves of 8μm-14μm, and the effective infrared short-wave and infrared medium-wave bands are completely filtered out, resulting in the inability to image normally. When used, even if the same type of filter film is selected according to the type of strong light such as sunlight and laser beams to avoid irreversible burns to the detector, it still affects the normal detection and imaging of the corresponding infrared band.

[0005] Patent CN114353954A proposes a method and system for preventing infrared thermal imagers from sunburn, which adds additional sensors to obtain the field of view of the thermal imager, obtain the azimuth information of the sun, obtain the azimuth information of the infrared thermal imager's visual axis, determine the position of the sun and the field of view of the thermal imager, and provide anti-sunburn protection. This increases the cost of the device to prevent sunburn, affects the timeliness of transmission, and has a probability of failure. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method and device for preventing sunburn of an infrared thermal imager, which can prevent sunburn without affecting the normal imaging of areas outside the solar radiation patches on the focal plane of the infrared detector.

[0007] The method for preventing infrared thermal imagers from being sunburned proposed by the present invention utilizes the characteristic that the high temperature of the sun causes the detector output data to be saturated, and includes the following three steps:

[0008] The first step is to add a solar radiation detection algorithm to the infrared thermal imager. The specific detection steps are as follows:

[0009] (1) Set the anti-sunburn algorithm switch, which is turned on by default;

[0010] (2) For each frame of image data output by the detector, detect whether the pixel value of the current scene image is greater than a saturation threshold of one;

[0011] (3) Determine the area of ​​the continuous region of pixels greater than the saturation threshold, that is, whether the concentration of the points is greater than the pixel number threshold 2;

[0012] (4) detecting the current image data, and if both threshold 1 and threshold 2 are satisfied, taking the solar radiation position as the solar radiation position, activating the solar burn prevention device, and shielding the pixel position corresponding to the solar radiation on the focal plane;

[0013] (5) Then continue to detect new image data to see whether it satisfies the judgment conditions of threshold 1 and threshold 2 at the same time. If so, move the sunburn protection device to the position; if not, turn off the sunburn protection device, and continue the cycle of detection and execution;

[0014] The second step is to implement the sunburn prevention device; the sunburn prevention device is composed of two strip polarized light filters that can transmit infrared band light, a transmission device, and a movable frame, and is installed on the front side of the detector. The two filters are vertically crossed at 90 degrees in the light transmission direction and move independently. The overlapping area of ​​the two polarized light films is not transparent; according to the solar radiation detection algorithm, the moving target position of the filter is moved so that the overlapping area of ​​the two polarized light films covers the solar radiation imaging position of the focal plane of the infrared detector;

[0015] In the third step, the image processing brightness is automatically adjusted; if no solar radiation is detected in the first step, the anti-sunburn device will not be executed, and the two polarized light filters are located outside the detector window and do not block the light path; if solar radiation is detected, the brightness of the row and column where the current polarized filter is located is compensated according to the position information of the filter.

[0016] The specific steps of the compensation method are as follows:

[0017] (1) For a horizontally mounted filter, the brightness change trend of each column is counted in the vertical direction, and the pixel brightness change of each column is detected, that is, all the differences in the brightness changes of the pixel row at the beginning of the polarization filter blocking and the pixel row at the end of the blocking are counted, and after removing the extreme noise difference, the average difference is calculated as the brightness compensation value of the horizontal polarization filter blocking area;

[0018] (2) For the vertically mounted filter, the brightness change trend of each row is counted in the horizontal direction, and the brightness change of each row of pixels is detected, that is, all the differences in the brightness changes of the pixel columns at the beginning and the end of the polarization filter are counted, and after removing the extreme noise differences, the average difference is calculated as the brightness compensation value of the vertical polarization filter blocked area;

[0019] (3) For polarization filter overlap, since solar radiation energy is completely blocked, a constant nSunshine=1000 needs to be added to the neighboring pixel value as the simulated data of the solar radiation area. After summing, it is not greater than the saturation threshold of one.

[0020] Through the above steps, the method for preventing sunburn of an infrared thermal imager proposed by the present invention is realized.

[0021] The present invention also provides an infrared thermal imager sun protection device, which is composed of two strip polarized light filters that can transmit infrared band light, a transmission device, and a movable frame, and is installed on the front side of the detector. The two filters are vertically crossed at 90 degrees in the light transmission direction and move independently. The overlapping area of ​​the two polarized light filters is not transparent.

[0022] The present invention relates to a method for preventing infrared thermal imagers from being burned by the sun. When an infrared detector is used, it directly faces the sun, which emits strong infrared rays, which can easily burn the detector and form bad spots on the surface of FPA, thus affecting the use of the detector.

[0023] The method of the present invention directly judges solar radiation by detecting the output data value of the detector, and performs periodic detection, which has high reliability. Then, two strip polarized light sheets in perpendicular directions are installed vertically in front of the focal plane of the detector as an execution device to prevent sunburn. Not only the focal plane position of solar radiation is shielded from burns, but also other areas can be imaged, and the scene outside the sun will not be blocked and information will not be lost. Then, the polarization brightness attenuation is compensated by the automatic image brightness adjustment algorithm to simulate solar imaging, which is in line with the visual habits of the human eye.

[0024] The beneficial effects of the method of the present invention are:

[0025] (1) There is no need to completely block the light path by closing the shutter to avoid missing the scene observation in the time segment.

[0026] (2) There is no need to use filters to attenuate the infrared imaging band, which would cause a significant decrease in the image signal-to-noise ratio and loss of scene detail information.

[0027] (3) There will be no loss of part of the scene information due to occlusion of a certain width caused by the light-blocking strip. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The figure is a flow chart of the method of the present invention.

[0029] Figure 2 This is a schematic diagram of the solar radiation protection device in the disabled state.

[0030] Figure 3 This is a schematic diagram of the solar radiation protection device enabled state. DETAILED DESCRIPTION

[0031] The present invention provides a method for preventing sun burns of an infrared thermal imager, and the specific process is as follows.

[0032] The first step is to add a solar radiation detection algorithm to the infrared thermal imager. The specific detection steps are as follows:

[0033] (1) Set the anti-sunburn algorithm switch, which is turned on by default;

[0034] (2) For each frame of image data output by the detector, detect whether the pixel value of the current scene image is greater than the saturation threshold 1; the setting of the threshold 1 is related to the bit data output by each pixel. For example, the effective bit width of the original infrared output data is 14 bits, and the maximum value is 2exp(14)=16383. The threshold 1 is slightly smaller than the maximum value and can be 16300.

[0035] (3) Determine whether the continuous area of ​​the pixel points greater than the saturation threshold, that is, whether the concentration of the points is greater than the second pixel number threshold; Threshold 2 is used to confirm the minimum value of the pixel area of ​​the connected domain of solar radiation imaging. Its setting is related to both the area of ​​the solar imaging pixel and the size of the bad pixel patch on the focal plane of the detector; for example, the size of the bad pixel connected domain is generally required to be less than 2*2, and the area of ​​the solar radiation imaging pixel is generally greater than 4*4. In this case, the value of Threshold 2 can be 3*3=9 pixels.

[0036] (4) If the judgment conditions of threshold 1 and threshold 2 are met at the same time, the anti-sunburn device is activated as the solar radiation position to block the pixel position corresponding to the solar radiation on the focal plane, that is, the vertical filter and the horizontal filter of the anti-sunburn device both block the solar imaging pixel position.

[0037] (5) Since the infrared thermal imager may be moved during use, the solar radiation position may change. Continue to detect whether the current scene image satisfies the judgment conditions of threshold 1 and threshold 2 at the same time. If so, there is a new solar radiation position, and move the anti-sunburn device to the position. If there is no new solar radiation position that satisfies the judgment conditions of threshold 1 and threshold 2 at the same time, turn off the anti-sunburn device, detect again, and execute the cycle.

[0038] The second step is to implement the anti-sunburn device. The anti-sunburn device consists of two strip polarized light filters that can project infrared band light, a transmission device, and a movable frame. It is installed on the front side of the detector. The light transmission directions of the two filters are vertically crossed at 90 degrees and can be moved in layers without interfering with each other. For example, the first strip filter is transparent in the vertical polarization direction, installed horizontally, and can be moved up and down; the second filter is transparent in the horizontal polarization direction, installed vertically, and can be moved left and right. The overlapping area of ​​the two polarized light films is not transparent. The moving target position of the mobile filter is executed according to the solar radiation detection position, so that the overlapping area of ​​the two polarized light films covers the solar radiation imaging position of the focal plane of the infrared detector.

[0039] The third step is to automatically adjust the image processing brightness. If no solar radiation is detected in the first step, the sunburn protection device will not be executed, and the two polarized light filters are located outside the detector window and do not block the light path; if solar radiation is detected, the brightness of the row and column where the current polarized filter is located is compensated according to the position information of the filter. The specific compensation method steps are as follows:

[0040] (1) For a horizontally mounted filter, the brightness change trend of each column is counted in the vertical direction, and the pixel brightness change of each column is detected, that is, all the differences in the brightness changes of the pixel row at the beginning of the polarization filter blocking and the pixel row at the end of the blocking are counted, and after removing the extreme noise difference, the average difference is calculated as the brightness compensation value of the horizontal polarization filter blocking area;

[0041] (2) For the vertically mounted filter, the brightness change trend of each row is counted in the horizontal direction, and the brightness change of each row of pixels is detected, that is, all the differences in the brightness changes of the pixel columns at the beginning and the end of the polarization filter are counted, and after removing the extreme noise differences, the average difference is calculated as the brightness compensation value of the vertical polarization filter blocked area;

[0042] (3) For polarization filter overlap, because the solar radiation energy is completely blocked, a constant nSunshine=1000 needs to be added to the neighboring pixel value as the simulated data of the solar radiation area. After summing, it is not greater than the saturation threshold of one.

Claims

1. A method for preventing sunburn of an infrared thermal imager, characterized in that: It includes the following three steps: The first step is to add a solar radiation detection algorithm to the infrared thermal imager. The specific detection steps are as follows: (1) Set the anti-sunburn algorithm switch, which is turned on by default; (2) For each frame of image data output by the detector, detect whether the pixel value of the current scene image is greater than a saturation threshold of one; (3) Determine the area of ​​the continuous region of pixels greater than the saturation threshold, that is, whether the concentration of the points is greater than the pixel quantity threshold 2; (4) detecting the current image data, and if both threshold 1 and threshold 2 are satisfied, taking the solar radiation position as the solar radiation position, activating the solar burn prevention device, and shielding the pixel position corresponding to the solar radiation on the focal plane; (5) Then continue to detect new image data to see whether it satisfies the judgment conditions of threshold 1 and threshold 2 at the same time. If so, move the sunburn protection device to the position; if not, turn off the sunburn protection device, and continue the cycle of detection and execution; The second step is to implement the sunburn prevention device; the sunburn prevention device is composed of two strip polarized light filters that can transmit infrared band light, a transmission device, and a movable frame, and is installed on the front side of the detector. The two filters are vertically crossed at 90 degrees in the light transmission direction and move independently. The overlapping area of ​​the two polarized light films is not transparent; according to the solar radiation detection algorithm, the moving target position of the filter is moved so that the overlapping area of ​​the two polarized light films covers the solar radiation imaging position of the focal plane of the infrared detector; In the third step, the image processing brightness is automatically adjusted; if no solar radiation is detected in the first step, the anti-sunburn device will not be executed, and the two polarized light filters are located outside the detector window and do not block the light path; if solar radiation is detected, the brightness of the row and column where the current polarized filter is located is compensated according to the position information of the filter.

2. The method according to claim 1, characterized in that In the third step, if solar radiation is detected, the brightness of the row and column where the current polarization filter is located is compensated according to the position information of the filter. The specific steps of the compensation method are as follows: (1) For a horizontally mounted filter, the brightness change trend of each column is counted in the vertical direction, and the pixel brightness change of each column is detected, that is, all the differences in the brightness changes of the pixel row at the beginning of the polarization filter blocking and the pixel row at the end of the blocking are counted, and after removing the extreme noise difference, the average difference is calculated as the brightness compensation value of the horizontal polarization filter blocking area; (2) For the vertically mounted filter, the brightness change trend of each row is counted in the horizontal direction, and the brightness change of each row of pixels is detected, that is, all the differences in the brightness changes of the pixel columns at the beginning and the end of the polarization filter are counted, and after removing the extreme noise differences, the average difference is calculated as the brightness compensation value of the vertical polarization filter blocked area; (3) For polarization filter overlap, since solar radiation energy is completely blocked, a constant nSunshine=1000 needs to be added to the neighboring pixel value as the simulated data of the solar radiation area. After summing, it is not greater than the saturation threshold of one.

3. An infrared thermal imager sun protection device, characterized in that: It consists of two strip polarized light filters that can transmit infrared light, a transmission device, and a movable frame. It is installed on the front side of the detector. The light transmission directions of the two filters are vertically crossed at 90 degrees and move independently.

4. The infrared thermal imager sun protection device according to claim 3, characterized in that: The first strip filter transmits light in the vertical polarization direction, is installed horizontally, and can be moved up and down; the second filter transmits light in the horizontal polarization direction, is installed vertically, and can be moved left and right.

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