JP2009089138A - Infrared ray camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that conventional camera is delivered while writing the sensitivity correction data of a detector in an ROM (read only memory), however, error is generated from the obtained data by radiant heat from a mirror cylinder or an optical system when photographing is effected in an environment different from that upon obtaining the data and the effect of image correction, obtained originally from the error, is lowered or the effect of image correction is lowered in the same manner when secular change is generated in image sensor characteristics after the delivery, and to obtain the image, which is not influenced by such the environment wherein the camera is placed or the secular change of the image sensor characteristics and reduced in the existence of fixed pattern. <P>SOLUTION: Uniform temperature (shutter) is photographed by the imaging element. The electric charge accumulating time (time of exposure) of the imaging element is changed and an image data A is stored upon the charge accumulating time A. An image data B is stored upon the charge accumulating time B. A difference between the image data A and the image data B becomes sensitivity data. The producing of the sensitivity data and image correcting operation employing the sensitivity data are effected to obtain the maximum image correction effect. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an infrared camera.

  In the conventional infrared camera, the sensitivity correction data is constant depending on the element temperature. Therefore, when the element temperature changes, the sensitivity characteristic changes, a correction shift occurs, and the fixed pattern noise is conspicuous in the image. As countermeasures, sensitivity correction data acquired in advance is stored in a memory, and image correction is performed based on the data to reduce fixed pattern noise (see, for example, Patent Document 1).

JP 2005-236550 A

However, when imaging is performed in an environment where the radiant heat from the lens barrel or optical system is different from the radiant heat at the time of sensitivity correction data acquisition, an error occurs from the acquired sensitivity correction data, so the effect of image correction originally obtained is low. There was a problem of becoming.
In addition, when an aging change occurs in the image sensor characteristics, there is a problem that the sensitivity correction data cannot be sufficiently corrected and the effect of image correction is reduced.

  The present invention has been made to solve such problems, and an object of the present invention is to obtain an infrared camera with less fixed pattern noise regardless of the environment in which the camera is placed and the secular change in the characteristics of the imaging device.

  The infrared camera according to the present invention includes an infrared optical system, an image pickup element positioned on the image forming plane of the infrared optical system, and a surface installed at a position where the visual field of the image pickup element can be covered when closed. And a signal processing display means connected to the image pickup device, and the signal processing display means is different in the image pickup device when the shutter is closed. Sensitivity correction data is acquired by taking the difference between the output results captured in the above accumulation time, and the sensitivity correction of the output of the image sensor is performed using the sensitivity correction data.

  According to the infrared camera of the present invention, an image with little fixed pattern noise can be obtained with a simple configuration without being influenced by the environment at the time of imaging and the secular change in sensitivity of the imaging device.

Embodiment 1 FIG.

First, the problems of the conventional infrared camera will be described.
In general, an infrared camera has a slightly different sensitivity value for each pixel. Therefore, when an object with a different temperature is imaged, uneven sensitivity appears in the image. For this reason, sensitivity data of all pixels is acquired at the adjustment stage at the time of manufacturing the camera, and sensitivity correction data is created from this sensitivity data and stored in the image memory inside the camera.
Sensitivity correction data G (n, T) is G (n, T) = Rave / R (n, T) (Formula 1)
It is represented by Here, Rave is an average value of the sensitivities of all the pixels, and R (n, T) is a sensitivity at the temperature T at the pixel number n.
The arithmetic circuit of the infrared camera calculates the image output Vout after the sensitivity correction from the element correction Vsig (n, T) at the temperature T at the pixel number n and the element output Vsig (n, T) according to Equation 2, for example.
Vout = Vsig (n, T) · G (n, T) (Formula 2)
However, in the conventional infrared camera, it was assumed that the sensitivity correction data was constant according to the element temperature of the image sensor. However, since the sensitivity characteristic of the element changes when the element temperature actually changes, the same sensitivity correction is performed. There was a problem that correction correction occurred in the data, and fixed pattern noise was conspicuous in the image.

  Here, an infrared camera with a small fixed pattern noise generated in the image as described above is obtained with a simple configuration.

Next, the infrared camera according to the present embodiment will be described.
FIG. 1 is a block diagram of an infrared camera according to the first embodiment.
In the figure, 1 is an infrared optical system, 2 is an image pickup device positioned on the image plane of the infrared optical system 1, 3 is an analog signal processing circuit that performs analog processing such as amplifying the output from the image pickup device 2, and 4 is An A / D conversion circuit that quantizes the output of the analog signal processing circuit, 5 is an image data arithmetic circuit that performs image correction using sensitivity correction data, and 6 converts the output of the image data arithmetic circuit 5 into a video output and outputs it. A D / A conversion circuit, 7 is a timing generation circuit that generates an element driving clock to be applied to the image sensor 2 from the image sensor driver circuit 8, and 9 is installed at a position that can cover the field of view of the image sensor 2 when closed. The shutter 10 has a uniform temperature, 10 is an element package for housing the image pickup element 2, and 11 is a part of the element package, which is an infrared window that transmits infrared rays. Note that the inside of the element package 10 is held in a vacuum. A sensitivity correction data RAM 12 stores sensitivity correction data.

  51 is an image data RAM-A, 52 for storing image data when each pixel of the image sensor stores tA (time) for accumulating infrared rays from the object. Similarly, each pixel of the image sensor Image data RAM-B and 53 for storing image data at tB (time) store image data output from the A / D conversion circuit 4 in either the image data RAM-A51 or the image data RAM-B52. A write selection circuit 54 for selecting these is a sensitivity correction data calculation circuit for calculating sensitivity correction data using the image data RAM-A51 and the image data RAM-B52 and outputting the result to the sensitivity correction data RAM12. A circuit from the output of the image sensor to the output of an image is referred to as signal processing display means.

Next, the sensitivity correction data acquisition operation of the infrared camera according to the present invention will be described.
FIG. 2 is a diagram showing an overview of the operation of acquiring sensitivity correction data.
In acquiring sensitivity correction data, first, the shutter of the infrared camera is closed (S01), and different accumulation times tA and tB in which the image sensor accumulates charges are set (S02). Next, the imaging device performs imaging at the accumulation time tA (S03) and imaging at the accumulation time tB (S04), and calculates sensitivity correction data (S05). When the sensitivity correction data is obtained, the acquisition operation is completed, the shutter is opened (S06), and the normal imaging mode is entered.

Next, details of the sensitivity correction data acquisition operation will be described below. Note that the entire operation is controlled by the control unit 60.
First, when a power source (not shown) of the infrared camera is turned on and imaging becomes possible after a predetermined time has elapsed, the control unit 60 closes the shutter 9 and sets the incident light amount to the image sensor to 0. The image sensor 2 captures an image of the shutter 9, which is a surface having a uniform temperature.
Sensitivity correction data for correcting the sensitivity of the captured image is acquired by imaging the shutter 9 in this manner.
This sensitivity correction data acquisition may be performed automatically when imaging is possible after the power is turned on, or immediately before imaging is actually started by the imaging device in a power-on state. When sensitivity correction is required, it can be performed by an external command. Sensitivity correction may be performed at predetermined time intervals.

3 and 4 are diagrams for explaining a method of calculating sensitivity correction data according to the first embodiment.
The imaging can be performed after the power is turned on, and the control unit 60 of the infrared camera outputs an instruction to close the shutter 9 when the sensitivity correction data is acquired or when the sensitivity correction data acquisition command is issued.
After the shutter 9 is closed, the control unit 60 sets two different accumulation times tA and tB as the signal for starting the acquisition of sensitivity correction data and the accumulation time for obtaining the sensitivity correction data to the timing generation circuit 7. Output a signal.
The timing generation circuit 7 sets the timing so that the accumulation time for accumulating the infrared rays from the shutter 9 is tA (time), and outputs an element drive clock to the image sensor driver circuit 8. The image sensor driver circuit 8 applies an element drive clock for driving each pixel to the image sensor 2. The image sensor 2 outputs the image signal Vsig (n, tA) at the accumulation time tA (time) to the A / D conversion circuit 4 through the analog signal processing circuit 3. Here, Vsig (n, tA) represents the output voltage at the pixel number n and the accumulation time tA (time) when the sensitivity correction data is acquired.
The control unit 60 controls the A / D conversion circuit 4 to cause the write selection circuit 53 to output the output Vsig (n, tA) of the image sensor 2 input through the analog signal processing circuit 3.
On the other hand, the timing generation circuit 7 receives the signal for starting the acquisition of the sensitivity correction data, and the A / D conversion circuit 4 performs A / D conversion on the previous Vsig (n, tA) to the write selection circuit 53. A signal for storing Vsig_ad (n, tA) in the image data RAM-A51 which is one of the image data RAMs is output.
The write selection circuit 53 that has received the command stores the data Vsig_ad (n, tA) after A / D conversion in the image data RAM-A51.

Next, in a state where the shutter 9 remains closed, the timing generation circuit 7 sets the timing so that the accumulation time for accumulating the infrared rays from the shutter 9 is tB (time), and sets the element drive clock to the image sensor driver. Output to the circuit 8. The image sensor driver circuit 8 applies an element drive clock for driving each pixel to the image sensor 2. The image sensor driver circuit 8 applies an element drive clock for driving each pixel to the image sensor 2. The image sensor 2 outputs an image signal Vsig (n, tB) having an accumulation time tB (time) to the A / D conversion circuit 4 through the analog signal processing circuit 3. Here, Vsig (n, tB) represents the output voltage at the pixel number n and the accumulation time tB (time) when the sensitivity correction data is acquired.
The control unit 60 controls the A / D conversion circuit to output the output Vsig (n, tB) of the image sensor 2 input through the analog signal processing circuit 3 to the writing selection circuit 53.
On the other hand, the timing generation circuit 7 sends the data Vsig_ad (n, tB) obtained by A / D converting the previous Vsig (n, tB) by the A / D conversion circuit 4 to the write selection circuit 53 as 1 in the image data RAM. A signal to be stored in one image data RAM-B52 is output.
Upon receiving the command, the write selection circuit 53 stores the data Vsig_ad (n, tB) after A / D conversion in the image data RAM-B52.

  The storage times tA and tB are on the order of, for example, several tens of milliseconds. However, the storage times tA and tB may be on the order of microseconds depending on the imaging environment, such as the accuracy required for correction and the time required for correction, and may take several seconds. May be.

When Vsig_ad (n, tB) is stored in the image data RAM-B52, the control unit 60 next outputs a control signal for execution of calculation to the sensitivity correction data calculation circuit 54, and sensitivity correction data calculation that receives this control signal. The circuit 54 calculates the difference between the data Vsig_ad (n, tA) stored in the image data RAM-A51 and the data Vsig_ad (n, tB) stored in the image data RAM-B52. That is, the sensitivity correction data GS (n) before calibration is GS (n) = Vsig_ad (n, tB) −Vsig_ad (n, tA) (Formula 3)
It is represented by Here, G (n) represents the sensitivity at pixel number n.
In this way, the infrared camera of the present invention acquires pre-calibration sensitivity correction data GS (n) for each pixel of the image sensor.

In each pixel of the image sensor, the difference in output of each pixel when the accumulation time is the same is considered to correspond to the sensitivity of each pixel. On the other hand, the image pickup device has an offset output even when the amount of incident light is zero.
Therefore, in the present embodiment, the difference between the outputs at different accumulation times is obtained, and the ratio of the differences is calculated so that it is used as sensitivity correction data for each pixel.

Next, a method in which the sensitivity correction data calculation circuit 54 calculates the sensitivity correction data G (n) based on the pre-calibration sensitivity correction data GS (n) will be described.
The sensitivity correction data calculation circuit 54 calculates sensitivity correction data G (n) used for correcting the sensitivity of the image of the object using the sensitivity correction data GS (n) before calibration. Here, an example thereof will be described with reference to FIG.
FIG. 4 is a diagram for explaining a method of calculating sensitivity correction data according to the present embodiment. In the figure, the pixel number of the pixel at the center position of the two-dimensional image sensor 2 is C.
Sensitivity correction data G (n) for each pixel is calculated by the following Equation 4.
G (n) = GS (n) / GS (C) (Formula 4)
As described above, the sensitivity correction data GS (C) before calibration in the pixel at the center position of the two-dimensional imaging device, that is, the image signal Vsig (C, tA) with the accumulation time tA (time) and the accumulation time tB (time ) Image signal Vsig (C, tB) as a reference, the ratio of the pre-calibration sensitivity correction data GS (n) of each pixel (pixel number n) arranged in two dimensions is calculated. The calculation result is defined as sensitivity correction data G (n).

  When the sensitivity correction data calculation circuit 54 calculates the sensitivity correction data G (n) of each pixel in this way, the result G (n) is stored in the sensitivity correction data RAM 12.

When the sensitivity correction data G (n) is stored in the sensitivity correction data RAM 12 in this manner, the control unit 60 finishes acquiring the sensitivity correction data to the timing generation circuit 7 assuming that the sensitivity correction data acquisition step is completed. The signal is output, the shutter 9 is opened, and the infrared camera is set to a normal image-capable state.
That is, the shutter 9 is opened, infrared light from the object is incident on the image sensor 2, and the image sensor driver circuit 8 applies an element drive clock to the image sensor 2 in accordance with the timing generated by the timing generation circuit 7. The image sensor 2 images the object. The analog signal processing circuit 3 outputs an image signal of each pixel of the image sensor 2 to the A / D conversion circuit 4. The A / D conversion circuit 4 outputs the data after A / D conversion to the image data calculation circuit 5.
The image data arithmetic circuit 5 performs sensitivity correction for each pixel using the sensitivity correction data G (n) stored in the sensitivity correction data RAM 12, and outputs the result to the D / A conversion circuit 6. The D / A conversion circuit 6 outputs the video output.

  As described above, in this embodiment, by controlling the accumulation time so as to obtain a plurality of types of sensitivity correction data, the shutter that is a subject only needs to have a uniform temperature. There is no need to change the temperature. For this reason, the shutter may have a simple structure.

According to the present embodiment, in the imaging environment, the sensitivity correction data is acquired based on the pixel output results at different accumulation times immediately before the imaging, and therefore the sensitivity correction data changes depending on the element temperature of the imaging device. Alternatively, even when the image sensor characteristics change over time, sensitivity correction data at the element temperature at the time of imaging can be obtained, and as a result, an image with little fixed pattern noise can be obtained.

In the example (see FIG. 4) of calculating the sensitivity correction data G (n) described earlier in Equation 4, the ratio of each pixel is calculated based on the pixel at the center position of the two-dimensional image sensor, and used as sensitivity correction data. However, for example, the two-dimensional image sensor may be divided into a plurality of blocks, and sensitivity correction data may be calculated in each block.
FIG. 5 is a diagram for explaining another method of calculating sensitivity correction data. As shown in FIG. 5, the image sensor 2 may be divided into a plurality of blocks (1 to n), and sensitivity correction data may be calculated in each block in the same manner as described in FIG.

  In the sensitivity correction data calculation method described in FIG. 4, the ratio of each pixel is calculated based on the pixel at the center position of the two-dimensional image sensor. For example, the pixel at the center position and the pixel at the corner position are calculated. An average of the outputs of a plurality of pixels may be calculated, and the ratio of each pixel output may be calculated based on the average value as sensitivity correction data.

  In the example described with reference to FIG. 3, the sensitivity correction data is calculated from two different accumulation times. However, in order to increase the accuracy of the sensitivity correction data, three or more different accumulation times (tA, tB, tC, ..)) May be obtained, and the result may be stored in the image data RAM. Then, the sensitivity correction data may be calculated by linear approximation or curve approximation based on the results of the three or more different accumulation times.

1 is a block diagram of an infrared camera according to Embodiment 1. FIG. FIG. 5 is a diagram showing an outline of sensitivity correction data acquisition operation according to the first embodiment. 6 is a diagram illustrating a method for calculating sensitivity correction data according to Embodiment 1. FIG. 6 is a diagram illustrating a method for calculating sensitivity correction data according to Embodiment 1. FIG. 6 is a diagram for explaining another calculation method of sensitivity correction data according to Embodiment 1. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Infrared optical system, 2 Image sensor, 3 Analog signal processing circuit, 4 A / D conversion circuit, 5 Image data arithmetic circuit, 6 D / A conversion circuit, 7 Timing generation circuit, 8 Image sensor driver circuit, 9 Shutter, DESCRIPTION OF SYMBOLS 10 Temperature stabilization container, 11 Infrared transmission window, 12 Sensitivity correction data RAM, 51 Image data RAM-A, 52 Image data RAM-B, 53 Write selection circuit, 54 Sensitivity correction data arithmetic circuit, 60 Control part

Claims (3)

Infrared optical system, image sensor located on the imaging plane of the infrared optical system, a shutter installed at a position covering the field of view of the image sensor when closed, and a uniform temperature within the surface, and driving the image sensor A driver circuit, and a signal processing display means connected to the image sensor and the driver circuit,
The signal processing display means obtains sensitivity correction data based on a ratio of the differences by taking a difference between the outputs obtained by capturing the images with two or more different accumulation times when the image pickup device is closed with the shutter closed. An infrared camera, wherein the sensitivity of the output of the image sensor is corrected using data. The signal processing display means includes a memory for storing each output result obtained by imaging the shutter at two or more different accumulation times when the image sensor is in a closed state, and sensitivity correction based on a difference between the output results. The infrared camera according to claim 1, further comprising: sensitivity correction data calculation means for calculating data; and image data calculation means for correcting the sensitivity of the output of the vapor imaging device using the sensitivity correction data. The infrared camera according to claim 1, wherein the signal processing unit calculates the ratio of the difference based on a pixel at a center position of the pixels constituting the image sensor.

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