JP7542400B2 - Infrared camera with temperature compensation effect control function - Google Patents

Description

This disclosed technology relates to an infrared camera equipped with a temperature correction effect control function.

In the technical field of infrared cameras that detect infrared radiation emitted from an object and display a thermal image showing the temperature distribution of the object, a technique has been disclosed for correcting fluctuations in observed temperature due to outside air temperature (for example, Patent Document 1).

Japanese Patent Application Publication No. 10-38684

In the conventional technology exemplified in Patent Document 1, the temperature drift correction process involves temperature monitoring at a sampling period ΔTime, and the need for correction is determined at discrete times. This causes the amount of correction to increase discontinuously, which causes the video signal to fluctuate discontinuously. In other words, infrared cameras using conventional technology have the problem that the temperature drift correction function can actually have a negative effect on the video signal.

The disclosed technology aims to solve the above problems and provide an infrared camera that prevents discontinuous large fluctuations in the video signal when the observed temperature fluctuates due to the outside air temperature while still allowing the temperature drift correction function of the infrared camera to function.

The infrared camera according to the disclosed technology is an infrared camera equipped with a temperature sensor that detects the outside air temperature and a correction unit that monitors the temperature data from the temperature sensor and corrects the video signal. The correction unit includes a temperature drift correction processing unit that generates a correction amount to eliminate temperature drift that accompanies changes in the outside air temperature, and a low-pass filter that is connected downstream of the temperature drift correction processing unit and processes the correction amount at a sampling period shorter than the monitoring of the temperature data . The low-pass filter included in the correction unit linearly interpolates the outputs of two moving average filters having different numbers of stages and outputs the results.

The infrared camera according to the disclosed technology has the above configuration, so that when the observed temperature fluctuates due to the outside air temperature, the temperature drift correction function works and the video signal does not fluctuate significantly and discontinuously.

FIG. 1 is a block diagram illustrating an example of a configuration of a system including an infrared camera according to a first embodiment. FIG. 2 is a block diagram showing a configuration of the infrared camera according to the first embodiment. FIG. 3 is a graph showing temperature drift correction according to the prior art. FIG. 4 is a graph showing temperature drift correction according to the disclosed technique. FIG. 5 is a graph showing the operation of the variable-length low-pass filter in the infrared camera according to the second embodiment. FIG. 6 is a schematic diagram showing markers displayed on an information layer of a camera image in an infrared camera according to the third embodiment.

The form for implementing the disclosed technology will be made clear by the following explanation along with the drawings.

Embodiment 1.
Fig. 1 is a block diagram showing an example of the configuration of a system including an infrared camera 1 according to embodiment 1. As shown in Fig. 1, the system including the infrared camera 1 according to embodiment 1 includes the infrared camera 1, a lens 2, a controller 3, a recording device 4, a monitor 5 for checking images, a power source 6, a control cable 7, a video cable 8, and a power cable 9.

The controller 3 sends commands to the infrared camera 1 via the control cable 7, and performs settings for the infrared camera 1, etc. The infrared camera 1 also captures an image of the subject, converts it into video data, and transmits the generated video data to the recording device 4 via the video cable 8. The recording device 4 receives the video data sent from the infrared camera 1, outputs the video to the monitor 5 for video confirmation, and records the video data. The power source 6 supplies power to operate the infrared camera 1 via the power cable 9.

Fig. 2 is a block diagram showing the configuration of the infrared camera 1 according to the first embodiment. As shown in Fig. 2, the infrared camera 1 according to the first embodiment is composed of a sensor 10, a signal processing unit 11, a temperature sensor 12, a correction unit 13, and a display processing unit 14.

The sensor 10 converts the infrared rays input through the lens 2 into an electrical signal and outputs the converted electrical signal to the signal processing unit 11. The signal processing unit 11 converts the electrical signal output from the sensor 10 into image data that can be visualized, and performs various correction processes such as contrast correction and noise reduction. The correction unit 13 also has a temperature drift correction processing unit 13a and a low-pass filter 13b. The temperature drift correction processing unit 13a monitors the temperature data obtained from the temperature sensor 12, and when a certain temperature change is detected, performs temperature drift correction on the image data converted by the signal processing unit 11. The low-pass filter 13b can be, for example, an FIR filter such as a moving average filter. The correction unit 13 corrects the output of the sensor 10, which changes due to the influence of temperature drift. The signal processing unit 11 outputs the image data on which various correction processes have been performed to the display processing unit 14. The display processing unit 14 superimposes on-screen displays of temperature data, date and time data, etc., onto the video data output from the signal processing unit 11, and outputs the resulting video signal to the external recording device 4 via the video cable 8.

The operation of the infrared camera 1 according to the first embodiment will be made clear by the explanation based on the following figures. In order to clarify the characteristics of the operation of the infrared camera 1 according to the disclosed technology, the figures are provided to allow a comparison between the conventional technology and the disclosed technology. FIG. 3 is a graph showing temperature drift correction according to the conventional technology. FIG. 4 is a graph showing temperature drift correction according to the disclosed technology. The upper graphs of FIGS. 3 and 4 are graphs showing the time series of the temperature detected by the temperature sensor 12, and the lower graphs of FIGS. 3 and 4 are graphs showing the time series of the correction amount corresponding to the upper graphs.

As shown in Figure 3, the temperature drift correction in the conventional infrared camera 1 is configured to monitor the temperature data from the temperature sensor 12 at a sampling period ΔTime, and execute temperature drift correction when the amount of change ΔTmp from the reference temperature exceeds a certain amount. In the temperature drift correction according to the conventional technology, when the temperature drift is large, the amount of correction also becomes large, and the video signal may fluctuate greatly and discontinuously.

The infrared camera 1 according to the disclosed technology includes a low-pass filter 13b, downstream of the temperature drift correction processing unit 13a, that operates at a sampling period Ts shorter than the sampling period ΔTime for temperature monitoring. Here, the shorter the sampling period Ts of the low-pass filter 13b, the more pronounced the effect of the disclosed technology. The low-pass filter 13b processes the correction amount generated by the temperature drift correction processing unit 13a. In this way, the disclosed technology divides and executes the temperature drift correction as shown in FIG. 4, reducing the amount of correction per time. This reduces the amount of correction even when the temperature drift is large, and prevents the video signal from fluctuating significantly and discontinuously.

4 is a time series graph showing the correction amount when a five-stage moving average filter with a length of five sampling periods is used as the low-pass filter 13b. If the input to the five-stage moving average filter is u _k and the output is y _k , the input/output relationship can be expressed by the following equation.
y _k = (u _k-4 +u _k-3 +u _k-2 +u _k-1 +u _k )÷5...(1)
When the input signal to a five-stage moving average filter is a step signal, the output signal is a staircase-like signal consisting of five steps, as shown in the lower graph of FIG.

The filter characteristics of the low-pass filter 13b, such as a moving average filter, are made adjustable as needed. For example, if the low-pass filter 13b is a moving average filter, it is made adjustable to output the average of the past number of pieces of data. In the example of the graph in the lower part of Figure 4, a five-stage moving average filter is shown, but the disclosed technology is configured so that this number of stages can be changed as needed. This allows the infrared camera 1 according to the disclosed technology to obtain a more appropriate correction effect according to its own characteristics and the surrounding environment.

With the above configuration, the infrared camera 1 according to the first embodiment has the advantage that, when the observed temperature fluctuates due to the outside air temperature, the temperature drift correction function works and the video signal does not fluctuate significantly and discontinuously.

Embodiment 2.
The technique according to the first embodiment has been described by taking a moving average filter as a specific example of the low-pass filter 13b. The low-pass filter 13b included in the infrared camera 1 according to the disclosed technique is not limited to a simple moving average filter. The low-pass filter 13b included in the infrared camera 1 according to the second embodiment has an upper limit set in advance for the magnitude of the change in the correction amount. When the change in the correction amount exceeds the upper limit set in advance, the low-pass filter 13b changes the filter characteristics according to the change in the correction amount so that the change in the correction amount does not exceed the upper limit. When the low-pass filter 13b is realized by a moving average filter, the change in the filter characteristics is to increase the moving average section. As a result, the change in the correction amount does not exceed the predetermined upper limit, and the video signal does not fluctuate discontinuously.

Figure 5 is a graph showing the action of the variable-length low-pass filter 13b in the infrared camera 1 according to the second embodiment. Figure 5A shows a specific example in which the variable-length low-pass filter 13b is a five-stage moving average filter, and shows a state in which the change in the correction amount exceeds the upper limit. Figure 5B shows a specific example in which the variable-length low-pass filter 13b increases the moving average interval to eight sampling periods (8 x Ts). Figure 5B shows that by increasing the moving average interval, the change in the correction amount becomes smaller, and the change in the correction amount does not exceed the upper limit.

The operation of the variable-length low-pass filter 13b will be made clearer by the following concrete example. In this concrete example, it is assumed that the variable-length low-pass filter 13b is initially a five-stage moving average filter. The variable-length low-pass filter 13b stores the output at the previous sampling time. The output at the previous sampling time is compared with the output at the current sampling time to determine whether the magnitude of the change in the correction amount exceeds the upper limit. If the magnitude of the change in the correction amount exceeds the upper limit, the moving average section is increased by the sampling period Ts, and the filter is first changed to a six-stage moving average filter with one more stage. If the magnitude of the change in the correction amount still exceeds the upper limit, another stage is added, followed by seven stages, eight stages, and so on.

When it is desired to make more detailed corrections than by increasing the number of moving average filters by one stage at a time, the variable-length low-pass filter 13b may employ a method represented by the following equation.
y _k =λ{(u _k-4 +u _k-3 +u _k-2 +u _k-1 +u _k )÷5}
+(1-λ) {(u _k-5 +u _k-4 +u _k-3 +u _k-2 +u _k-1 +u _k )÷6}...(2)
where λ is a parameter expressed by a real number from 0 to 1. Equation (2) is an equation that gives a value for interpolating between a 5-stage moving average filter and a 6-stage moving average filter. When λ=1, equation (2) is the same as a 5-stage moving average filter. When λ=0, equation (2) is the same as a 6-stage moving average filter. The infrared camera according to the second embodiment may be configured to appropriately adjust the parameter λ from 0 to 1 to finely adjust the amount of correction.

With the above configuration, the infrared camera 1 according to the second embodiment adjusts the amount of correction more finely than the first embodiment, preventing discontinuous large fluctuations in the video signal.

Embodiment 3.
The techniques according to the first and second embodiments relate to temperature drift correction of the infrared camera 1, and to adjusting the amount of correction to prevent discontinuous large fluctuations in the video signal. In the technical field of infrared cameras, when temperature drift correction is frequently performed, calibration is required afterwards. Calibration here refers to a correction operation performed to suppress variations within the surface of the sensor and maintain the temperature indication accuracy.

Calibration of the infrared camera 1 is usually performed with the mechanical shutter closed. In this case, since the video signal cannot be updated during calibration, the video signal may continue to output a still image from immediately before calibration is performed. The fact that the image does not move means that it is impossible to determine from the image whether the infrared camera 1 is undergoing calibration or not. The infrared camera 1 according to the third embodiment has a function for displaying information related to the calibration in addition to the functions shown in the first or second embodiment.

Figure 6 is a schematic diagram showing markers displayed on the information layer of the camera image in the infrared camera 1 according to the third embodiment. As shown in Figure 6, the camera image can display information layers superimposed thereon to display various information in addition to information actually captured by the lens. Markers can be displayed on the display layer, and the mode, status, or state of the infrared camera 1 can be expressed by the color of the marker. Specific examples shown in Figure 6 are as follows: When the marker is black, it indicates that calibration is not in operation. When the marker is red, it indicates that calibration is in operation, triggered by the passage of a specified time. When the marker is green, it indicates that calibration is in operation, triggered by the occurrence of a specified temperature change. Furthermore, when the marker is blue, it indicates that calibration is in operation manually, based on an instruction from a switch on the main unit, a remote control, a communication command, or the like.

The messages indicated by the above marker colors are merely examples, and the combination of color and message may be freely designed. Furthermore, notification of information may be configured to change the shape of the marker instead of changing the color of the marker. Furthermore, the position of the marker in the information layer shown in Figure 6 is in the bottom left corner, but this is not limited to this.

While FIG. 6 shows an example in which the markers are displayed on the camera image, this is not limiting. Information about the markers, etc. may be sent to downstream processing of the camera. Examples of downstream processing of the camera include discrimination processing such as object detection, and temperature measurement processing for measuring a person's body temperature, etc. Such a configuration has the effect of allowing downstream processing of the camera to know that the infrared camera 1 is undergoing calibration.

Furthermore, the marker of the infrared camera 1 according to the third embodiment may represent the state of the low-pass filter 13b in the infrared camera 1 according to the second embodiment. Possible uses of the marker include placing the number 0 next to the marker when the low-pass filter 13b is not used at all, placing the number 5 next to the marker when the low-pass filter 13b is a five-stage moving average filter, and placing the number 6 next to the marker when the low-pass filter is a six-stage moving average filter.

With the above configuration, the infrared camera 1 according to the third embodiment changes the display of the marker depending on the calibration execution state and the state of the low-pass filter 13b. Therefore, the calibration execution state of the camera and the state of the low-pass filter 13b can be known from the camera image, etc.

The disclosed technology can be used, for example, in an infrared camera that detects infrared radiation emitted from the human body and displays a thermal image showing the distribution of body temperature.

1 Infrared camera; 2 Lens; 3 Controller; 4 Recording device; 5 Monitor; 6 Power supply; 7 Control cable; 8 Video cable; 9 Power cable; 10 Sensor; 11 Signal processing section; 12 Temperature sensor; 13 Correction section; 13a Temperature drift correction processing section; 13b Low-pass filter; 14 Display processing section.

Claims (4)

A temperature sensor for detecting an outside air temperature;
An infrared camera comprising a correction unit that monitors temperature data from the temperature sensor and corrects an image signal,
the correction unit includes a temperature drift correction processing unit that generates a correction amount for eliminating a temperature drift caused by a change in the outside air temperature, and a low-pass filter that is connected to a stage subsequent to the temperature drift correction processing unit and processes the correction amount at a sampling period shorter than a period for monitoring the temperature data,
The low-pass filter included in the correction unit performs linear interpolation on the outputs of two moving average filters having different numbers of stages and outputs the results.
Infrared camera. The low-pass filter provided in the correction unit has an input at the k-th sampling time u k and an output y k , where n is the order and λ is a parameter representing a real number from 0 to 1, as follows:

Represented by
2. The infrared camera according to claim 1. The correction unit determines whether or not a magnitude of a change in the correction amount generated by the low-pass filter exceeds a predetermined upper limit;
When the magnitude of the change in the correction amount exceeds an upper limit, λ in the formula shown in claim 2 is changed.
3. The infrared camera according to claim 2 . An infrared camera according to any one of claims 1 to 3 ,
Notifying a marker indicating whether calibration is in progress or not;
Identifying and notifying an execution status of the calibration being performed based on a color or a shape of the marker;
Infrared camera.

Images