JP6989330B2 - Infrared camera for temperature detection - Google Patents

Description

The present invention relates to a temperature detection infrared camera that obtains a thermal image for temperature detection.

An infrared camera that detects infrared rays emitted from an object and obtains a thermal image has been conventionally used for various thermal analyzes. Infrared cameras have the excellent feature of being able to measure the temperature distribution instantly without contact, so the range of applications is expanding.

For example, one frame of a thermal image captured by a conventional infrared camera is composed of 320 horizontal pixels and 240 vertical pixels, which is called the QVGA (Quarter Video Graphics Array) standard.

Patent Document 1 describes an example in which temperature control of a facility (temperature control of a waste treatment plant) is performed using a thermal image captured by an infrared camera.

Japanese Unexamined Patent Publication No. 2000-113344

In recent years, the number of pixels of captured images has been increasing in cameras that capture visible light, and there is a demand for an increase in the number of pixels in thermal images obtained by infrared cameras for temperature detection. As the number of pixels of the thermal image increases, the thermal distribution of the monitored object can be detected with higher accuracy. For example, by increasing the number of pixels, there is a possibility that even a slight temperature change that was previously overlooked can be detected.

However, on the receiving terminal side that receives and analyzes the thermal image output by the infrared camera for temperature detection, as the number of pixels of the thermal image increases, the amount of arithmetic processing for analyzing the thermal image increases accordingly. For example, when the thermal image is changed from the QVGA standard (horizontal 320 pixels x vertical 240 pixels) to the VGA standard (horizontal 640 pixels x vertical 480 pixels), the number of pixels of the thermal image in one frame is quadrupled and the amount of calculation processing is increased. Will increase four times. When the amount of arithmetic processing increases in this way, a high-performance receiving terminal (computer) that performs arithmetic processing is required to have a large amount of information processing, and it is assumed that the conventional terminal does not have sufficient capacity.

Also, regarding the transmission path for transmitting the thermal image signal from the infrared camera to the receiving terminal, it is necessary to support the transmission of four times the amount of information by changing from the QVGA standard to the VGA standard. Therefore, in order to improve the image quality of the infrared camera, it is necessary to take measures to increase the transfer rate also for the transmission line.

If the transfer rate of the transmission line is not sufficient, for example, an infrared camera may compress the thermal image data and transmit it to the receiving terminal. However, in the case of the lossless compression method in which the data can be restored to the original state on the receiving side, the compression rate is not so high and it is not very effective. In addition, when a lossy compression method with low resilience on the receiving side is applied, a high compression ratio can be obtained, but since the data restored on the receiving side contains errors, an erroneous temperature is detected at the receiving terminal. As a result, there is a possibility of false alarm output and alarm omission. Furthermore, it is necessary to equip the infrared camera with a thermal image data compression function and the receiving terminal with a thermal image data restoration function, which is disadvantageous in terms of an increase in equipment cost, an increase in calculation load, and an increase in processing delay.

In addition, as another countermeasure when the transfer rate of the transmission line is not sufficient, it is conceivable to transmit only a part of the thermal image with the infrared camera for temperature detection, or to lower the frame rate of the thermal image. However, in either case, the ability of the infrared camera for temperature detection is not utilized, which is not preferable.

The present invention provides an infrared camera for temperature detection that can obtain a high-resolution thermal image and reduce the burden on a terminal that acquires and processes the high-resolution thermal image and the burden during transmission. With the goal.

The infrared camera for temperature detection of the present invention has an infrared sensor that captures a thermal image having a first number of pixels and a maximum value and a minimum value for the thermal image captured by the infrared sensor in units of blocks having a predetermined number of pixels. It is provided with a representative value calculation unit for calculating as a representative value, and an output unit for outputting a thermal image having a second number of pixels obtained by reducing the number of pixels.
Here, the first block processed by the representative value calculation unit has the maximum value in the block as the representative value, and the second block processed by the representative value calculation unit has the minimum value in the block as the representative value.

According to the present invention, a thermal image with a reduced number of pixels can be output while taking advantage of the high resolution of the thermal image captured by the infrared sensor. Therefore, it is possible to construct a system capable of monitoring with a high-resolution thermal image while reducing the burden on the terminal and the transmission line for analyzing the thermal image.

It is a block diagram which shows the structural example of the infrared camera by one Embodiment of this invention. It is a figure which shows the pixel composition example (A: composition example of an image pickup pixel, B: composition example of a pixel after calculation of a representative value) of the infrared camera by one Embodiment of this invention. It is a flowchart which shows the processing example (the example which outputs the maximum value or the minimum value) by the example of one Embodiment of this invention. It is a flowchart which shows the processing example (the example which outputs the difference between the maximum value and the minimum value) by the example of one Embodiment of this invention. It is explanatory drawing which shows the example of the thermal image by one Embodiment of this invention.

Hereinafter, an example of an embodiment of the present invention (hereinafter referred to as “this example”) will be described with reference to the accompanying drawings.

[1. Configuration of infrared camera for temperature detection]
FIG. 1 shows a configuration example of the temperature detection infrared camera 10 of this example.
The temperature detection infrared camera 10 of this example includes an infrared sensor 11, an infrared correction processing unit 12, a representative value calculation unit 13, an output unit 14, and a control unit 15.

The infrared sensor 11 is an infrared image sensor that acquires a thermal image with a VGA standard pixel arrangement (horizontal 640 pixels x vertical 480 pixels). The thermal image data acquired by the infrared sensor 11 is supplied to the infrared correction processing unit 12. Here, each pixel of the thermal image data acquired by the infrared sensor 11 is, for example, 16-bit data, and the infrared sensor 11 obtains thermal image data of 30 frames per second.
The infrared correction processing unit 12 performs correction processing for converting the thermal image data supplied from the infrared sensor 11 into thermal image data from which appropriate temperature information can be obtained. The thermal image data corrected by the infrared correction processing unit 12 is supplied to the representative value calculation unit 13.

The representative value calculation unit 13 reduces the number of pixels of the thermal image data of the VGA standard pixel array and converts it into the thermal image data of the QVGA standard pixel array (horizontal 320 pixels × vertical 240 pixels). The details of the representative value calculation process in the representative value calculation unit 13 will be described later. The QVGA standard thermal image data obtained by reducing the number of pixels in the representative value calculation unit 13 is supplied to the output unit 13.

The output unit 13 outputs QVGA standard thermal image data to the outside of the temperature detection infrared camera 10. In the example of FIG. 1, the output unit 13 and the receiving terminal 20 are connected by a cable, and the QVGA standard thermal image data is transmitted from the output unit 13 to the receiving terminal 20. When the infrared sensor 11 obtains thermal image data at 30 frames per second, the output unit 13 also outputs (transmits) the thermal image data at 30 frames per second.

When the output unit 13 and the receiving terminal 20 are connected by a network such as a LAN (Local Area Network), the output unit 13 becomes a communication interface suitable for the network. When QVGA standard thermal image data in which one pixel is composed of 16 bits is transmitted to the receiving terminal 20 at 30 frames per second, the transfer rate is 320 × 240 × 16 bits × 30 = about 37 Mbps. For example, in the case of a LAN, this can be transmitted using a device called 100BASE, which is a standard capable of transferring a maximum of 100 Mbps. When transferring a VGA standard thermal image as it is, a transfer rate of 147 Mbps, which is four times higher, is required, and it cannot be transferred by a LAN of 100BASE standard.

The correction processing in the infrared correction processing unit 12, the representative value calculation processing in the representative value calculation unit 13, and the output processing in the output unit 14 are executed under the control of the control unit 15. For example, the representative value calculation unit 13 has a plurality of processing modes as the representative value calculation process, and it is determined in which mode the representative value calculation unit 13 performs the representative value calculation process by a command from the control unit 15. do.

The receiving terminal 20 receives the thermal image data transmitted from the temperature detection infrared camera 10 and analyzes and monitors the thermal image.

[2. Example of representative value calculation process]
Next, the details of the representative value calculation process performed by the representative value calculation unit 13 will be described.
FIG. 2A shows a pixel array before the representative value calculation process, and FIG. 2B shows a pixel array after the representative value calculation process. In FIGS. 2A and 2B, the horizontal axis shows the X coordinate, which is the coordinate in the horizontal direction, and the vertical axis shows the Y coordinate, which is the coordinate in the vertical direction. The number in each square indicates the pixel number. The pixel number is [. ] Indicates the X coordinate, and [. ] Indicates the Y coordinate.

As a pixel array before the representative value calculation process, which is a pixel array acquired by the infrared sensor 11, as shown in FIG. 2A, the first horizontal line (top horizontal line) is the pixel of [1.1]. , [2.1] pixel, [3.1] pixel, ..., The next horizontal line (second horizontal line) is the [1.2] pixel, [2.2]. , Pixel of [3.2], ..., And the data of the pixel of each horizontal line is arranged in the same manner below.

Here, in this example, four adjacent pixels are treated as one block, and one pixel data as a representative value is calculated for each block. That is, as shown in FIG. 2A by enclosing each pixel with a thick line, one block is formed by four pixels (2 pixels in the X direction) × (2 pixels in the Y direction), and the representative value calculation unit 13 is used. The representative value calculation process is performed so that only one pixel data is output for each block.
For example, as shown in FIG. 2B, the pixel [1.1] of the thermal image data calculated by the representative value calculation unit 13 is the four pixels [1.1] and [2.1] shown in FIG. 2A. , [1.2], [2.2] are designed to output one pixel data as a representative value.
The representative value calculation process for each block is performed to convert the VGA standard thermal image data into the QVGA standard thermal image data.

Next, when the representative value calculation process is performed in each block, the pixel data generation process that is output after the representative value calculation will be described.
The flowchart of FIG. 3 shows a processing example when the first processing mode is set.
First, the representative value calculation unit 13 acquires data of 4 pixels in one block (step S11). Then, the representative value calculation unit 13 determines the pixel having the maximum pixel value (temperature) among the acquired four-pixel data (step S12).
When the maximum value is determined in step S12, the representative value calculation unit 13 sets the output value of the pixel of the block after the representative value calculation to the determined maximum value (step S13). When the output pixel value of one block is determined in step S13, the representative value calculation unit 13 returns to the process of step S11 and moves to the process of the next block.

In this way, when the first processing mode is set, the representative value calculation unit 13 selects the pixel data having the maximum value (maximum temperature) for each block, and outputs the selected pixel data.
In the example of FIG. 3, the maximum value is determined and output for each block, but the minimum value is determined for each block and the pixel data that becomes the minimum value (minimum temperature) is output. You may try to do it.

When this first processing mode is set, the temperature detection infrared camera 10 effectively reduces the number of pixels of the output thermal image while taking advantage of the high resolution of the thermal image acquired by the infrared sensor 11. be able to. That is, since the resolution of the thermal image is determined by the number of pixels of the infrared sensor 11, a high-resolution thermal image can be obtained by obtaining a VGA standard thermal image. For example, when only one very small range of temperatures becomes very hot, that high temperature can be accurately detected in a thermal image.

Then, when the representative value calculation unit 13 performs the representative value calculation process, the pixel with the maximum value is selected for each block, so that the high temperature detected by the infrared sensor 11 is output as it is. One pixel of a low-resolution thermal image can be considered as an average of a plurality of pixels of a high-resolution thermal image. Therefore, when the maximum value for each block is adopted as the representative value, the minute high-temperature portion is output without being averaged, as in the case of using a high-resolution thermal image. Therefore, in the receiving terminal 20, monitoring is performed using a QVGA standard thermal image, but the temperature monitoring of the monitoring location can be monitored at the maximum temperature with a high resolution similar to the case of monitoring with a VGA standard thermal image. can.

By setting the first processing mode in this way, it becomes possible to monitor the temperature with high resolution by using the conventional capability as the transmission line and the receiving terminal 20 for transmitting the thermal image data as they are. For example, as a transmission path, when transmitting QVGA standard thermal image data in which one pixel is composed of 16 bits to the receiving terminal 20 at 30 frames per second as described above, the transfer rate is generally about 37 Mbps. Transfer is possible on the LAN network of the 100BASE standard, which is the transmission system used. Further, the receiving terminal 20 also has the ability to monitor the thermal image of the QVGA standard, and has the ability to substantially monitor the thermal image of the VGA standard, so that the ability to monitor the thermal image can be improved. ..
When the place where the temperature is monitored by the infrared camera 10 for temperature detection is monitored to be low temperature, the representative value calculation unit 13 performs the representative value calculation process as the second processing mode. The minimum pixel value may be selected for each block.

Next, a processing example when the third processing mode shown in the flowchart of FIG. 4 is set will be described.
First, the representative value calculation unit 13 acquires data of 4 pixels in one block (step S21). Then, the representative value calculation unit 13 determines, among the acquired four-pixel data, the pixel having the maximum pixel value (temperature) and the pixel having the minimum pixel value (temperature) (step S22).
Next, the representative value calculation unit 13 calculates the difference between the maximum value and the minimum value determined in step S22 (step S23). Then, the representative value calculation unit 13 sets the output value of the pixel of the block after the representative value calculation process to the value of the difference calculated in step S23 (step S24). When the output pixel value of one block is determined in step S24, the representative value calculation unit 13 returns to the process of step S21 and moves to the process of the next block.

In this way, when the third processing mode is set, the representative value calculation unit 13 selects the data of the difference between the maximum value and the minimum value for each block, and outputs the pixel data of the selected difference value.

When this third processing mode is set, the thermal image data output by the temperature detection infrared camera 10 shows the maximum temperature difference of each block. Therefore, in the receiving terminal 20, each block (each output pixel). The temperature difference can be monitored well with high resolution.
FIG. 5 shows an example of the monitoring state when the third processing mode is applied. Here, the high temperature point H exists in the thermal image P1, and the receiving terminal 20 accurately detects the edge part (contour) of the high temperature point H and determines to which coordinate position the high temperature point H is. It is to monitor.

When monitoring is performed in such an application, by setting the third processing mode, as shown in FIG. 5, for example, the representative value pixel of the block b1, the representative value pixel of the block b2, and so on, in that order. When is obtained, the block b3 that detects the heat of the edge portion of the high temperature portion H becomes the maximum temperature difference.
Therefore, in the receiving terminal 20 that receives the thermal image data with the number of pixels reduced, the edge portion of the high temperature portion H can be detected with the resolution of the original thermal image obtained by the infrared camera 10 for temperature detection.

[3. Modification example]
In the above-described embodiment, the thermal image obtained by the temperature detection infrared camera 10 has the number of pixels of the VGA standard, and the thermal image output after the representative value calculation process has the number of pixels of the QVGA standard. Yes, the infrared camera 10 for temperature detection may obtain a thermal image having another number of pixels. The point of reducing the number of pixels to 1/4 is also an example, and the number of pixels may be reduced to another.

The number of pixels in one block may also be changed. In the above-described embodiment, the number of pixels in one block when performing the representative value calculation process is 4 pixels (horizontal 2 pixels × vertical 2 pixels). It is an example that these two pixels are regarded as one block, and one block may be formed by the number of other pixels, and the representative value calculation process may be performed on a larger block.
Specifically, as a block of a unit of representative value calculation processing, it can be generalized as a block composed of N pixels × M pixels (N and M are arbitrary integers). When one block is composed of N pixels × M pixels, the pixels that cannot be divided by the block may be regarded as an independent minute region without being truncated.

Further, the frame rate of 30 frames per second shown in the above-described embodiment is also an example, and can be applied to obtain a thermal image at another rate.
Further, in the above-described embodiment, the same representative value calculation process is performed for all blocks, but different representative value calculation processes may be performed for each block. That is, for example, it may be possible to select the maximum value in one block of a certain thermal image, select the minimum value in another block, and select the difference between the maximum value and the minimum value in another block.
Further, if a representative value calculation process is performed with the maximum value, the minimum value, or the difference between the maximum value and the minimum value as the representative value for a part of the area (the area including at least one block) in the image, that area. Other representative value calculation processes may be applied to parts other than the above. As another representative value calculation process, there may be a pixel value at a fixed position in the block, an average value, a median value, or the like. That is, for example, in one block of one thermal image, the maximum value is selected, in another block, the minimum value is selected, and in another block, the maximum value, the minimum value, and the representative value different from the difference between the maximum value and the minimum value are different. It may be possible to select.
It may be constructed so that it can be changed by setting the selection of the representative value calculation process in each block in the control unit 15.

10 ... Infrared camera for temperature detection, 11 ... Infrared sensor, 12 ... Infrared correction processing unit, 13 ... Representative value calculation unit, 14 ... Output unit, 15 ... Control unit, 20 ... Receiving terminal, P1 ... Thermal image, H … High temperature points

Claims (2)

An infrared sensor that captures a thermal image with the first number of pixels,
A representative value calculation unit that calculates the maximum and minimum values as representative values in block units of a predetermined number of pixels for the thermal image captured by the infrared sensor.
The representative value calculation unit includes an output unit that outputs a thermal image having a second number of pixels obtained by reducing the number of pixels.
The first block processed by the representative value calculation unit uses the maximum value in the block as a representative value, and the second block processed by the representative value calculation unit uses the minimum value in the block as a representative value for temperature detection. Infrared camera for. Further, the representative value calculation unit performs a representative value calculation process in which the maximum value and the minimum value are different for the block subjected to the process in which the maximum value is the representative value and the blocks other than the block in which the minimum value is the representative value. The infrared camera for temperature detection according to claim 1, wherein the representative value is calculated in 1.

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