JP2005274301A - Infrared camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem in conventional infrared cameras in which no correction means of infrared radiation is available for camera components placed ahead of the shutter because the conventional infrared camera comprises a body with uniform temperature such as a shutter between an inside infrared optical system and an inside infrared imaging element, stores an image taken when the shutter closes as an offset, and makes an infrared image from an imaging target by subtracting the stored data from the whole signal. <P>SOLUTION: The infrared camera comprises a function which stores a typical shading pattern for an image of infrared radiation from the camera components in advance, and a function which detects the amount of shading by applying a low-pass filter to the image taken and measuring direct-current brightness of each part on the screen, generates correction data from the detected amount of shading and the shading pattern, and subtracts the obtained correction data from the imaged image data. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image correction process of an infrared camera.

  In addition to the infrared rays radiated from the imaging target, the infrared rays emitted from the infrared optical system and the casing that are components of the camera are simultaneously incident on the infrared imaging element of the infrared camera. The effect of infrared radiation from the infrared optical system or the case is usually called shading. The amount of shading is not a fixed amount, but the influence varies depending on the temperature state of the camera.

  Further, the amount of shading is a concentric pattern having a greater influence at the edge of the screen than at the center of the normal screen. In the conventional infrared camera, in order to cancel the infrared radiation from the above camera components, a shutter or the like is provided between the tip of the infrared optical system, the inside of the lens, or the infrared optical system inside the camera and the infrared imaging device. An image obtained when a uniform temperature object is provided and the shutter is closed is stored as an offset amount, and the stored data is subtracted from the entire signal and visualized as infrared rays from the imaging target (for example, Patent Document 1, Patent Document 2).

Japanese Patent No. 3373387 (first page, Fig. 1) Japanese Patent Laid-Open No. 11-46322 (first page, FIG. 1)

However, there is a problem that the mechanism of the infrared optical system is complicated in the method in which the shutter is provided at the tip of the infrared optical system or in the lens, and the method in which the shutter is provided in the camera has a simple configuration, but the infrared optical system There was a problem that the influence of infrared radiation from the system could not be canceled.
It is an object of the present invention to provide an infrared camera capable of effectively correcting the influence of shading caused by infrared radiation from components of an infrared camera such as an infrared optical system and a casing even when a shutter is provided inside the camera. Objective.

  An infrared camera according to the present invention includes a detector having a plurality of pixels, an amplifier circuit that amplifies the output signal of the detector, an analog low-pass filter that transmits a low-frequency component of the output signal of the amplifier circuit, and the analog An A / D conversion circuit that converts an output signal of the low-pass filter into digital data, an image storage memory that stores output data of the A / D conversion circuit, a shading pattern memory that stores predetermined shading pattern data, and the image A shading amount detection circuit for detecting a shading amount at substantially the same location as the predetermined shading pattern data measurement location from the image data stored in the storage memory, and shading in the shading pattern memory for the predetermined shading pattern data The amount of shading above the amount An image multiplier circuit for multiplying a coefficient based on the ratio of the shading amount obtained from the output circuit, and has an image subtraction circuit for subtracting the output data of the image multiplication circuit from the photographed image data.

  The infrared camera according to the present invention generates low-frequency component image data of an image separately from a captured video output system, and is generated at that time based on the difference in luminance between the central portion and the peripheral portion of the image data. By subtracting the shading correction data obtained by multiplying and subtracting the shading pattern data stored in advance based on the detection result, and subtracting it from the output video data It is possible to provide an infrared camera capable of removing the influence of infrared radiation on the captured image.

Embodiment 1 FIG.
1 is a block diagram showing a configuration of an infrared camera according to Embodiment 1 of the present invention. As shown in the figure, the infrared camera according to the first embodiment is an infrared optical system 1 such as an infrared optical system, a housing 2, and a detector installed on the image plane of the infrared optical system 1. It has a detector array 3.

  Here, the detector array 3 is, for example, a two-dimensional array of a plurality of pixels such as a bolometer and an SOI diode method. A shutter 4 is provided between the infrared optical system 1 and the detector array 3. As the shutter 4, for example, a material such as metal that tends to have a uniform temperature is selected. The detector array 3 is connected to an amplification circuit 6 that amplifies the output, an A / D conversion circuit 7, an offset correction memory 8, and a display processing circuit 9. Further, in the infrared camera according to this embodiment, a timing generation circuit 10 that generates element driving timing and shutter opening / closing timing, and a driver circuit 5 is connected between the timing generation circuit 10 and the detector array 3. .

  In addition to the above, the infrared camera according to the first embodiment has an analog low-pass filter 11 that transmits a low-frequency component and does not transmit a high-frequency component in the output signal of the detector array 3, and an output of the analog low-pass filter 11. Based on an A / D conversion circuit 12 that converts a signal into a digital signal, an image storage memory 13 that stores output data of the AD conversion circuit 12 in a two-dimensional memory, and luminance data of each pixel in the image storage memory 13 A shading amount detection circuit 14 for calculating a shading amount, a shading pattern memory 15 for storing a representative shading pattern in the combined infrared optical system 1, and data stored in the shading pattern memory 15 in advance. An image multiplying circuit 16 that multiplies the predetermined coefficient, the output data of the image multiplying circuit 16, and the display processing circuit 9 And an image subtracting circuit 17 which performs subtraction processing with the force data.

  Next, the operation will be described. First, the operation of the infrared camera when performing normal shooting will be described. In the infrared camera, the timing generation circuit 10 sends a drive clock to the detector array 3 via the driver circuit 5, and the detector array 3 receiving the drive clock outputs a video signal. Next, the timing generation circuit 10 sends a signal for closing the shutter 4 to the shutter 4. The detector array 3 outputs a voltage corresponding to the temperature of the detector constituting each pixel in a state where the shutter 4 is closed. After the signal voltage is amplified by the amplifier circuit 6, the A / D converter circuit 7 outputs the voltage. A / D conversion is performed and data is stored in the offset correction memory 8 for each pixel.

  Next, the shutter 4 is opened, and infrared rays emitted from the object to be imaged are imaged on the detector array 3 by the infrared optical system 1. A minute voltage difference occurs between the pixels due to the difference in the radiation amount of the imaging object, and the detector array 3 outputs a voltage corresponding to the temperature of each pixel. The signal voltage is amplified by the amplifier circuit 6 and then A / D converted by the A / D converter circuit 7. The display processing circuit 9 subtracts the data stored in the offset correction memory 8 for each pixel, A video signal based on the signal level when closed is generated.

  Subsequently, the shading removal procedure by infrared radiation of the infrared optical system 1 and the housing 2 will be described. The infrared camera according to this embodiment starts detecting the amount of shading, for example, at a fixed period or with a command from the outside of the infrared camera.

  When the shading amount detection process is started, the A / D conversion circuit 12 first converts the video signal of the amplifier circuit 6 that has passed through the analog low-pass filter 11 into digital data. The cutoff frequency of the analog low-pass filter 11 is determined based on the frequency when the shading amount is maximum.

  The output data of the A / D conversion circuit 12 is stored in the image storage memory 13 for each pixel. The shading amount detection circuit 14 uses the screen data of the image storage memory 13 and detects the currently occurring shading amount from, for example, the difference between the luminance data at the center of the screen and the four corners of the screen. The image multiplication circuit 16 multiplies an accurate shading pattern stored in the shading pattern memory 15 based on the detection result of the shading amount detected by the shading amount detection circuit 14 to obtain the optimum in the current state. Shading pattern data is generated. The image subtracting circuit 17 subtracts the output data of the image multiplying circuit 16 from the output data of the display processing circuit 9 to generate video data from which the influence of shading is removed.

FIG. 4 illustrates a procedure for generating the output data of the image multiplication circuit 16 from the captured image. Although this explanatory diagram is an operation explanation for only one horizontal line, the same processing may be performed on a plurality of lines in order to obtain luminance data at a plurality of locations on the screen. By passing the output signal of the amplification circuit 6 including the signal component of the shooting scene through the analog low-pass filter 11, data in which the signal component of the shooting scene is reduced is generated and stored in the image storage memory 13.
Luminance data at arbitrary coordinates is measured for the data stored in the image storage memory 13 and a coefficient A corresponding to the ratio between the currently generated shading amount and the shading pattern data stored in the shading pattern memory 15 is calculated. To do.

  Next, calculation of the coefficient A will be described with reference to FIG. First, the inclination between the screen center and the luminance data at each distance from the screen center is calculated in advance from the data in the shading pattern memory 15. FIG. 5 is an example of measuring four slopes T1 to T4 in one line. On the other hand, the shading amount detection circuit 14 calculates the gradients Ta to Td between the screen center and the luminance data at each distance from the screen center in the same manner for the data in the image storage memory 13. This is the same location as the pixel position where T1 to T4 of the shading pattern memory 15 are calculated. Then, for example, the coefficient A is determined by averaging the calculated ratio of the inclination of each pixel position. The number of screen lines and the number of pixels for calculating the slope for calculating the coefficient A are not particularly specified.

  By multiplying the accurate shading pattern data stored in advance in the shading pattern memory 15 by the calculated coefficient A, correction data reflecting both the shading pattern of the lens and the shading amount currently generated is obtained. Generated.

FIG. 4 illustrates a procedure for generating the output data of the image multiplication circuit 16 from the captured image. Although this explanatory diagram is an operation explanation for only one horizontal line, the same processing may be performed on a plurality of lines in order to obtain luminance data at a plurality of locations on the screen. By passing the output signal of the amplification circuit 6 including the signal component of the shooting scene through the analog low-pass filter 11, data in which the signal component of the shooting scene is reduced is generated and stored in the image storage memory 13.
Luminance data at arbitrary coordinates is measured for the data stored in the image storage memory 13, and a coefficient A corresponding to the currently generated shading gradient is calculated. By multiplying the accurate shading pattern data stored in advance in the shading pattern memory 15 by the calculated coefficient A, correction data reflecting both the shading pattern of the lens and the shading amount currently generated is obtained. Generated.

  FIG. 6 illustrates a situation where the output data of the image multiplication circuit 16 is subtracted from the output data of the display processing circuit 9. The image subtraction circuit 17 subtracts the output data of the display processing circuit 9 including shading from the output data of the image multiplication circuit 16 which is the predicted optimum shading pattern, thereby obtaining an image from which the influence of shading is removed. .

  As described above, the infrared camera according to this embodiment detects the shading amount based on the image storage memory 13 for storing the image data from which the high frequency component of the output data of the amplifier circuit 6 is removed, and the luminance gradient of the image. By providing the shading amount detection circuit 14 that performs the shading pattern memory 15 that stores the shading pattern, it is possible to remove the influence of the infrared radiation of the infrared optical system 1 and the housing 2.

Embodiment 2. FIG.
FIG. 2 is a block diagram showing the configuration of the second embodiment of the present invention. In this embodiment, a digital low-pass filter 18 is provided instead of the analog low-pass filter 11 and the A / D conversion circuit 12 in the first embodiment. The digital low-pass filter 18 is connected to the A / D conversion circuit 7.

  Next, the operation will be described. The infrared camera according to this embodiment starts detecting the amount of shading, for example, at a fixed period or with a command from the outside of the infrared camera. When the shading amount detection process is started, output data of the A / D conversion circuit 7 is first input to the digital low-pass filter circuit 18. The digital low-pass filter 18 has a characteristic that image data of each pixel input in time series transmits data below a predetermined cutoff frequency and does not transmit data above the cutoff frequency. The cut-off frequency of the digital low-pass filter 18 is determined based on the frequency when the shading amount is maximum.

  The output data of the digital low-pass filter 18 is stored in the image storage memory 13 for each pixel. The shading amount detection circuit 14 uses the screen data in the image storage memory 13 and detects the amount of shading currently occurring, for example, based on the difference in luminance data between the center of the screen and the four corners of the screen. The image multiplication circuit 16 multiplies an accurate shading pattern stored in the shading pattern memory 15 based on the shading amount detection result in the shading amount detection circuit 14 to obtain an optimum shading in the current state. Generate dating pattern data. The image subtracting circuit 17 subtracts the output data of the image multiplying circuit 16 from the output data of the display processing circuit 9 to generate video data from which the influence of shading is removed.

FIG. 6 illustrates a procedure for generating the output data of the image multiplication circuit 16 from the photographed image. Although this explanatory diagram is an operation explanation for only one horizontal line, the same processing may be performed on a plurality of lines in order to obtain luminance data at a plurality of locations on the screen. By passing the output signal of the A / D conversion circuit 7 including the signal component of the shooting scene through the digital low-pass filter 18, data in which the signal component of the shooting scene is reduced is generated and stored in the image storage memory 13.
Luminance data at arbitrary coordinates is measured for the data stored in the image storage memory 13 and a coefficient A corresponding to the ratio between the currently generated shading amount and the shading pattern data stored in the shading pattern memory 15 is calculated. To do.

    Next, calculation of the coefficient A will be described with reference to FIG. First, the inclination between the screen center and the luminance data at each distance from the screen center is calculated in advance from the data in the shading pattern memory 15. FIG. 5 is an example of measuring four slopes T1 to T4 in one line. On the other hand, the shading amount detection circuit 14 calculates the gradients Ta to Td between the screen center and the luminance data at each distance from the screen center in the same manner for the data in the image storage memory 13. This is the same location as the pixel position where T1 to T4 of the shading pattern memory 15 are calculated. Then, for example, the coefficient A is determined by averaging the calculated ratio of the inclination of each pixel position. The number of screen lines and the number of pixels for calculating the slope for calculating the coefficient A are not particularly specified.

  By multiplying the accurate shading pattern data stored in advance in the shading pattern memory 15 by the calculated coefficient A, correction data reflecting both the shading pattern of the lens and the currently generated shading amount is obtained. Generated.

FIG. 7 illustrates a procedure for generating the output data of the image multiplication circuit 16 from the photographed image. Although this explanatory diagram is an operation explanation for only one horizontal line, the same processing may be performed on a plurality of lines in order to obtain luminance data at a plurality of locations on the screen. By passing the output signal of the A / D conversion circuit 7 including the signal component of the shooting scene through the digital low-pass filter 18, data in which the signal component of the shooting scene is reduced is generated and stored in the image storage memory 13.
Luminance data at arbitrary coordinates is measured for the data stored in the image storage memory 13, and a coefficient A corresponding to the currently occurring shading gradient is calculated. By multiplying the accurate shading pattern data stored in advance in the shading pattern memory 15 by the calculated coefficient A, correction data reflecting both the shading pattern of the lens and the shading amount currently generated is obtained. Generated.

  As described above, the infrared camera according to this embodiment includes the image storage memory 13 for storing the image data from which the high frequency component of the output data of the A / D conversion circuit 7 is removed, and the shading based on the luminance gradient of the image. By providing the shading amount detection circuit 14 for detecting the amount and the shading pattern memory 15 for storing the shading pattern, it is possible to remove the influence of the infrared radiation of the infrared optical system 1 and the housing 2.

Embodiment 3 FIG.
FIG. 3 is a block diagram showing the configuration of the third embodiment of the present invention. The infrared camera according to this embodiment is obtained by adding an integration circuit 19 to the configuration of the infrared camera according to the second embodiment.

  Next, the operation will be described. The infrared camera according to this embodiment starts detecting the amount of shading, for example, at a fixed period or with a command from the outside of the infrared camera. When the shading amount detection process is started, output data of the A / D conversion circuit 7 is first input to the digital low-pass filter circuit 18. The digital low-pass filter 18 has a characteristic that image data of each pixel input in time series transmits data below a certain cutoff frequency and does not transmit data above the cutoff frequency. The cut-off frequency of the digital low-pass filter 18 is determined based on the frequency when the shading amount is maximum.

  Output data of the digital low-pass filter 18 is input to the integrating circuit 19. The integration circuit 19 generates and outputs average data for a certain period of the input data for each pixel. The output data of the integration circuit 19 is stored in the image storage memory 13 for each pixel. The shading amount detection circuit 14 uses the screen data in the image storage memory 13 and detects the amount of shading currently occurring, for example, based on the difference in luminance data between the center of the screen and the four corners of the screen. The image multiplication circuit 16 multiplies an accurate shading pattern stored in the shading pattern memory 15 based on the shading amount detection result in the shading amount detection circuit, and obtains an optimum shading in the current state. Generate dating pattern data. The image subtracting circuit 17 subtracts the output data of the image multiplying circuit 16 from the output data of the display processing circuit 9 to generate video data from which the influence of shading is removed.

  FIG. 4 is a diagram for explaining the operation of the integrating circuit 19. As shown in the figure, the integration circuit 19 generates average data for a plurality of screens in terms of output data of the digital low-pass filter 18 in terms of time. The generated data is stored in the image storage memory 13.

FIG. 8 illustrates a procedure for generating the output data of the image multiplication circuit 16 from the captured image. Although this explanatory diagram is an operation explanation for only one horizontal line, the same processing may be performed on a plurality of lines in order to obtain luminance data at a plurality of locations on the screen. By passing the output signal of the A / D conversion circuit 7 including the signal component of the photographed landscape through the digital low-pass filter 18, data in which the signal component of the photographed landscape is reduced is generated. Further, average data of the generated data for a certain time is generated by the integration circuit 19 and stored in the image storage memory 13.
Luminance data at arbitrary coordinates is measured for the data stored in the image storage memory 13 and a coefficient A corresponding to the ratio between the currently generated shading amount and the shading pattern data stored in the shading pattern memory 15 is calculated. To do.

  Next, calculation of the coefficient A will be described with reference to FIG. First, the inclination between the screen center and the luminance data at each distance from the screen center is calculated in advance from the data in the shading pattern memory 15. FIG. 5 is an example of measuring four slopes T1 to T4 in one line. On the other hand, the shading amount detection circuit 14 calculates the gradients Ta to Td between the screen center and the luminance data at each distance from the screen center in the same manner for the data in the image storage memory 13. This is the same location as the pixel position where T1 to T4 of the shading pattern memory 15 are calculated. Then, for example, the coefficient A is determined by averaging the calculated ratio of the inclination of each pixel position. The number of screen lines and the number of pixels for calculating the slope for calculating the coefficient A are not particularly specified.

  By multiplying the accurate shading pattern data stored in advance in the shading pattern memory 15 by the calculated coefficient A, correction data reflecting both the shading pattern of the lens and the amount of shading currently generated is generated. Is done.

  FIG. 9 is a diagram for explaining the operation of the integrating circuit 19. As shown in the figure, the integration circuit 19 generates average data for a plurality of screens in terms of the output data of the digital low-pass filter 18 in terms of time. The generated data is stored in the image storage memory 13.

  As described above, the infrared camera according to this embodiment is steadily generated by providing the integration circuit 19 that generates the time-series average data of the image from which the high-frequency component of the output data of the A / D conversion circuit 7 is removed. More accurate shading correction can be achieved by effectively detecting the shading and reducing the influence of the time-varying captured video.

It is a block diagram which shows the structure of the infrared camera concerning Embodiment 1 of this invention. It is a block diagram which shows the structure of the infrared camera concerning Embodiment 2 of this invention. It is a block diagram which shows the structure of the infrared camera concerning Embodiment 3 of this invention. It is operation | movement explanatory drawing of the image multiplication circuit in Embodiment 1 of this invention. It is operation | movement explanatory drawing of the shading amount detection circuit in Embodiment 1 thru | or Embodiment 3 of this invention. It is operation | movement explanatory drawing of the image subtraction circuit in Embodiment 1 thru | or Embodiment 3 of this invention. It is operation | movement explanatory drawing of the image multiplication circuit in Embodiment 2 of this invention. It is operation | movement explanatory drawing of the image multiplication circuit in Embodiment 3 of this invention. It is operation | movement explanatory drawing of the integration circuit in Embodiment 3 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Infrared optical system, 2 housing | casing, 3 detector array, 4 shutter, 5 driver circuit, 6 amplification circuit, 7 A / D conversion circuit, 8 offset correction memory, 9 display processing circuit, 10 timing generation circuit, 11 analog Low-pass filter, 12 A / D conversion circuit, 13 image storage memory, 14 shading amount detection circuit, 15 shading pattern memory, 16 image multiplication circuit, 17 image subtraction circuit, 18 digital low-pass filter, 19 integration circuit.

Claims (4)

A detector having a plurality of pixels;
An amplifier circuit for amplifying the output signal of the detector;
An analog low-pass filter that transmits the low-frequency component of the output signal of the amplifier circuit;
An A / D conversion circuit for converting the output signal of the analog low-pass filter into digital data;
An image storage memory for storing output data of the A / D conversion circuit;
A shading pattern memory storing predetermined shading pattern data;
A shading amount detection circuit for detecting a shading amount at substantially the same location as the predetermined shading pattern data measurement location from the image data stored in the image storage memory;
An image multiplying circuit that multiplies the predetermined shading pattern data by a coefficient based on a ratio of a shading amount obtained from the shading amount detection circuit to a shading amount in the shading pattern memory;
An image subtracting circuit for subtracting the output data of the image multiplying circuit from the captured image data;
An infrared camera characterized by comprising: A detector having a plurality of pixels;
An amplifier circuit for amplifying the output signal of the detector;
An A / D conversion circuit for converting the output signal of the amplifier circuit into digital data;
A digital low-pass filter that transmits a low-frequency component of output data of the A / D conversion circuit;
An image storage memory for storing output data of the digital low-pass filter;
A shading pattern memory storing predetermined shading pattern data;
A shading amount detection circuit for detecting a shading amount at substantially the same location as the predetermined shading pattern data measurement location from the image data stored in the image storage memory;
An image multiplying circuit that multiplies the predetermined shading pattern data by a coefficient based on a ratio of a shading amount obtained from the shading amount detection circuit to a shading amount in the shading pattern memory;
An image subtracting circuit for subtracting the output data of the image multiplying circuit from the captured image data;
An infrared camera characterized by comprising: The infrared camera according to claim 2, further comprising an integration circuit for generating temporal average data of output data of the digital low-pass filter. The image multiplying circuit multiplies a coefficient based on an arithmetic average of respective ratios at predetermined measurement positions with a shading amount obtained from the shading amount detection circuit with respect to a shading amount in the shading pattern memory. The infrared camera according to any one of claims 1 to 3.

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