JPH07253360A - Method and apparatus for removing fixed pattern-noise of infrared sensor - Google Patents

Abstract

PURPOSE:To pick up an image free from offset errors between lines by moving a predetermined heat source rod in front of an infrared sensor and obtaining a reference data memory to be used for removing fixed pattern noise. CONSTITUTION:As a heat source rod 13 moves, each infrared ray detecting element of an infrared sensor 3 detects infrared sequentially emitted from the rod 13 to input them into an ADD-converter 6, and obtained digital data is recorded in a reference data memory 8 as reference data. Then the reference data of a corresponding line is read out from the memory 8 and input to a noise calculation circuit 10b. The circuit 10b subtracts an average value held in an average calculation circuit 10a from the reference data of each infrared detecting element, thereby obtaining noise data for each line. Then a correction calculation circuit 11 subtracts horizontal line noise from data of each pixel sequentially output from an image data memory 7 to obtain image data with the noise removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixed pattern noise eliminator for an infrared sensor, and more particularly to a fixed pattern noise eliminator for an infrared sensor having no offset error between lines and elements.

[0002]

2. Description of the Related Art As shown in FIG. 12, a conventional infrared image pickup device collects infrared rays from an object through an optical system 101 and makes them incident on an infrared sensor 103. Although the infrared sensor 103 has a one-dimensional structure and a two-dimensional structure, when the infrared sensor 103 having a one-dimensional structure is used, the scanning mirror 102 interposed in the optical path is synchronized with the scanning of three electron beams on the monitor screen. As a result, the two-dimensional image is formed on the infrared sensor 103 with the lapse of time, and when the infrared sensor 103 having a two-dimensional structure is used, the scanning mirror 102 is unnecessary (or Fixed state).

The output of the infrared sensor 103 is shown in FIG.
As shown in FIG. 5, the image data amplified by the amplifier 104 and sequentially sent from the infrared detectors by the multiplexer 105
It is input to the / D converter 106. The analog image data input to the A / D converter 106 is converted into digital image data and recorded in the image data memory 107.

In this image data, characteristic error of each infrared detecting element and shading (caused by the amount of unnecessary background radiation varying depending on the position of the infrared detecting element 103)
Based noise (called fixed pattern noise) is included.

In order to correct the above noise, a method using a reference plate has been conventionally used. That is, the optical system 10
1. The front surface of the scanning mirror 102 or the infrared sensor 103 is covered with a reference plate made of a metal plate at a predetermined temperature, for example, room temperature, and the output of the infrared sensor 103 at this time is used as reference plate data for each horizontal line as a reference value memory. It is recorded in 108. In this state, the correction plate 109 obtains the corrected image data by subtracting the reference plate data of the corresponding horizontal line from the image data read from the image data memory 107, and the corrected image data is D /
It is output to a monitor such as a CRT via the A converter 110.

There is also a method called a DCR method which can correct data while continuing image pickup. That is, as shown in FIG. 14, the line average value calculation circuit 208
Then, the average value of the outputs of the infrared detection elements of each line of the image data of the previous frame is calculated, and this average value is recorded in the average value memory 209. In this state, the correction arithmetic circuit 109 subtracts the average value of the line of the previous frame of the average value memory 209 from the real-time image data of the image data memory 107 to obtain the corrected image data.

[0007]

As described above, the method using the reference plate has a drawback that image data cannot be obtained while the reference plate is interposed in the optical path.

On the other hand, the DCR method has a problem in that an offset error between lines depending on image data occurs and the error appears as horizontal stripes on the screen of the monitor.
That is, as shown in FIG. 15, in the horizontal line L1 in which the bright portion B is present when the image is captured one frame before, as indicated by the solid line in FIG. Since the level of the dark portion D is high, the average value of the horizontal line L1 including the dark portion D is higher than the level of the dark portion D as shown by the broken line in the figure.

On the other hand, in the horizontal line L2, which is all the dark area D, the level of the dark area D becomes an average value as shown in FIG. 16 (b), and the correction operation circuit is shown in FIG. 16 (c). The brightness of the dark portion B of the line that does not include the bright portion B becomes brighter than that of the dark portion D of the line that includes the bright portion B of the image data corrected by 109, and the surroundings appear dark. In particular, when the target object is moving, the problem that the brightness fluctuates for each screen and the screen flickers occurs.

In view of the above circumstances, the present invention provides an infrared sensor fixed pattern noise removal method and apparatus capable of performing image pickup without interruption of image data and without offset error between lines. The purpose is to

[0011]

The present invention employs the following means in order to achieve the above object. That is, as shown in FIG. 1, in a method of removing fixed pattern noise from image data of an infrared sensor 3 in which a plurality of infrared detecting elements are arranged one-dimensionally or two-dimensionally, a heat source of a predetermined temperature is provided in front of the infrared sensor 3. The heat source rod 1 is moved by moving the rod 13.
The fixed pattern noise is removed from the image data obtained at the time of imaging based on the reference data obtained corresponding to the movement of No. 3.

More specifically, the noise data is once generated from the reference data, and the noise data is subtracted from the image data in the correction arithmetic circuit 11. In this case, the reference data itself is used as the noise data. However, it is preferable to use the noise detection circuit 10 and use data obtained by subtracting the average value of the reference data from the reference data.

Further, as a matter of course, the reference data is stored in the reference data memory 8 so that the synchronization relationship with the image data is maintained.

[0014]

[Operation] According to the present invention, the heat source rod 13 constituting the infrared sensor 3 is moved in front of the infrared sensor 3, and the reference data is sampled corresponding to the movement of the heat source rod 13.

Ideally, the movement of the heat source rod 13 is synchronized with the sampling speed of the image data from the infrared sensor 3,
It is preferable to sample the reference data by suspending the acquisition of the image data for one screen. However, since it is difficult to synchronize the heat source rod 13 that is mechanically moved with the sampling speed of the image data as described later, the movement position of the heat source rod 13 on the infrared sensor 3 is grasped and synchronized with the position. Then, the reference data is sampled.

This makes it possible to take in reference data while displaying an image. In addition, the noise data generated by subtracting the average value corresponding to each display line of the reference data from the reference data eliminates the difference in offset caused by the temperature difference of each line accompanying the movement of the heat source rod 13. By subtracting this noise data from the image data, the offset difference between the lines can be removed, and the noise caused by the difference in the characteristics between the elements can also be removed.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the method of the present invention and the apparatus of the present invention will be described below with reference to the drawings. FIG. 2 is a block diagram showing an embodiment of the present invention. As shown in FIG. 3, the optical system 1 collects the incident light from the object to be imaged and irradiates the infrared sensor 3 via the scanning mirror 2. As before,
In the two-dimensional sensor, the scanning mirror 2 is fixed (or not used), but in the one-dimensional sensor, the scanning mirror 2 is swung at the timing synchronized with the sampling of the image data by the infrared sensor 3, and the two-dimensional sensor is used over time. It is designed to obtain a three-dimensional image.

Image data obtained from the infrared sensor 3 is amplified by an amplifier 4 as shown in FIG. 2, and is input to an A / D converter 6 by a multiplexer 5 in the order of arrangement of infrared detecting elements. After A / D conversion in 6,
It is recorded in the image data memory 7 as image data.

The image data recorded in the image data memory 7 contains the fixed pattern noise based on the shading due to the variation in characteristics among the elements forming the infrared sensor 3 as described above. To remove this fixed pattern noise, the following heat source rod 13 is used.

That is, the heat source rod 13 having a predetermined temperature moves to a specific direction on the image forming point on the infrared sensor 3 or on the plane P parallel to the infrared sensor 3 on the lens 1 _L side of the image forming point. To do. Then, the image data obtained corresponding to the movement of the heat source rod 13 is recorded in the reference data memory 8 as reference data for removing the fixed pattern noise.

The moving direction of the heat source rod 13 is determined by the order in which image data is taken out from each element constituting the infrared sensor 3, and in the example of the two-dimensional sensor shown in FIG. Since the image data is extracted toward, the movement of the heat source rod 13 is adjusted accordingly. Further, in the one-dimensional example shown in FIG. 7, it moves in the element array direction.

The heat source rod 13 is provided with a temperature monitoring unit 14 for waiting the writing of the reference data memory 8 until the temperature of the heat source rod 13 becomes uniform. The temperature monitoring unit 14 is, for example, as shown in FIG. , A large number of temperature sensors 15 arranged on the heat source rod 13 at appropriate intervals in the longitudinal direction thereof.
And a temperature data comparator 16 for comparing the outputs of these temperature sensors 15, and a writing request is made until the temperature of the heat source rod 13 becomes uniform after the temperature data comparator 16 starts energizing the heat source rod 13. The standby signal Wp is output to prohibit writing to the reference data memory 8.

In addition to the temperature sensor 15, a large number of Peltier elements 21b are arranged at appropriate intervals, and all the temperature sensors are heated and cooled by the Peltier elements 21b at each part of the heat source rod 13. The temperature data comparator 23 may output the write request standby signal Wp until the temperature data obtained from 15 become the same to prohibit writing to the reference data memory 8.

Further, the heat source rod 13 is horizontally reciprocally driven by a motor 17 such as a stepping motor which can accurately control the speed, as shown in FIG.
The lower portion 7 is fixed to the rail 7, and the upper end thereof is slidably supported by the rail 19. Then, the temperature monitoring unit 14 causes the heat source rod 1
After it is detected that the temperature of the infrared sensor 3 is uniform, the motor 17 is operated to cross the front surface of the infrared sensor 3. The position control by the motor 17 is performed by the position control means 20.
Therefore, the position control means 20 controls the heat source rod 13
The position of is always grasped and is used for writing reference data into the reference data memory 8 described below.

As the heat source rod 13 moves, the infrared sensor 3
Of the infrared detecting elements sequentially detect infrared rays radiated from the heat source rod 13, their outputs are amplified by the amplifier 4, arranged in time series in a predetermined order by the multiplexer 5, and input to the A / D converter 6. To be done. The digital data obtained here is recorded in the reference data memory 8 as reference data.

In this case, although not particularly limited, for example, as shown in FIG. 6, the area corresponding to the heat source rod 13 on the monitor screen is defined as one field, and as shown in FIG. 8, the first field from the left end of the monitor screen is displayed. , The acquired data of the second field, the acquired data of the second field, ..., The acquired data of the nth field, and so on. Corresponding reference data is captured. At this time, the position information of the position control means 20 is used to generate the write signal of the reference data memory 8 only at the sampling position corresponding to the position of the heat source rod 13.

Further, the number of pixels in the horizontal direction of the monitor screen is S
The number of pixels included in the width of the heat source rod 13, that is, the number of pixels in the horizontal direction that can capture data in one field is H, 1
If the processing time of the field is F (seconds), the time t (seconds) required to sample the reference data for one screen, that is, the time for the heat source rod 13 to move one screen is t = (S / H ) F. Here, it is ideal that the width of the heat source rod 13 is reduced to about one infrared detecting element (1 pixel), but if it is about 2 to several pixels, most of the monitor screen is the heat source rod 13. There is no practical problem because it is released from.

From the reference data recorded in the reference data memory 8 as described above, the output of each infrared detecting element of each horizontal line as shown in FIG. 9 is read out, and the average value calculation circuit 10a shows it in FIG. The average value of the outputs of the infrared detecting elements for one screen for each line is calculated, and the average value is held in the average value calculation circuit 10a. The average value becomes a different value for each line due to the sensitivity difference of the infrared sensor 3 accompanying the movement of the heat source rod 13 and the like, and the difference in the average value is the difference in the offset between the lines when the following processing is not performed ( It appears as a difference in brightness on the screen).

The reference data of the corresponding line is read from the reference data memory 8 at the same timing as the readout of each pixel from the image data memory 7, and the noise calculation circuit 10b is read.
To enter.

In the noise calculating circuit 10b, the average value held in the average calculating circuit 10a is subtracted from the reference data of each infrared detecting element of the line concerned, whereby the noise data of each line is obtained for each infrared detecting element. To be

Then, in the correction operation circuit 11, the noise of the corresponding horizontal line shown in FIG. 11 (2) is obtained from the data of each pixel in real time as shown in FIG. 11 (1) sequentially output from the image data memory 7. By subtracting
The image data from which noise is removed as shown in 1 (3) is obtained.

The image data corrected in this manner is input from the correction circuit 11 to the D / A conversion circuit 12, and the D / A conversion is performed.
After conversion, it is output to the monitor. While the data is being loaded into the reference data memory 8, real-time image data can be freely loaded into the image data memory 7, and therefore the reference data can be rewritten without interrupting the image.

However, the image of the heat source rod 13 is displayed on the monitor screen for the pixel which is facing the heat source rod 13 and whose data is being taken into the reference data memory 8.

In the above example, the temperature of the heat source rod 13 is controlled. However, as long as a substantially uniform temperature can be maintained, the heat source rod may be a very fine object that is not temperature controlled. Further, in the above embodiment, the noise detecting circuit 10 including the average value calculating circuit 10a and the noise calculating circuit 10b is provided to detect the noise component. The noise component obtained by this is
The effect of shading due to the position on the infrared detector will be reduced, and the brightness of the screen will be uniform.
Needless to say, the reference data may be directly subtracted from the image data without passing through the noise detection circuit 10.

[0035]

As described above, according to the present invention, the predetermined heat source rod is moved in the predetermined direction on the front surface of the infrared sensor to obtain the reference data memory used for removing the fixed pattern noise. There is an effect that the target can be imaged while sampling the reference data.

Moreover, when the average value of the outputs of the infrared detecting elements of one screen is obtained from the reference data and this average value is subtracted from the output of the infrared detecting elements of each column, the offset for each line due to the movement of the heat source rod There is no risk of error.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a functional block diagram of the present invention.

FIG. 3 is a configuration diagram of an optical system of the present invention.

FIG. 4 is a configuration diagram of a temperature monitoring unit of the present invention.

FIG. 5 is a configuration diagram of a heat source rod drive mechanism of the present invention.

FIG. 6 is an explanatory diagram showing the relationship between the heat source rod and the two-dimensional infrared sensor of the present invention.

FIG. 7 is an explanatory diagram showing the relationship between the heat source rod and the one-dimensional infrared sensor of the present invention.

FIG. 8 is an explanatory diagram of a reference data acquisition order of the present invention.

FIG. 9 is a voltage distribution diagram showing an example of reference data of one horizontal line of the present invention.

FIG. 10 is a voltage distribution diagram showing an average voltage of a reference data example of one horizontal line of the present invention.

FIG. 11 is an explanatory diagram showing a relationship between image data of the present invention and noise component-corrected image data.

FIG. 12 is a block diagram of an optical system of a conventional example.

FIG. 13 is a functional block diagram of a conventional example.

FIG. 14 is a functional block diagram of another conventional example.

FIG. 15 is a schematic diagram of another conventional monitor display screen.

FIG. 16 is an explanatory diagram of a function of another conventional line average arithmetic circuit.

[Explanation of symbols]

 3 Infrared sensor 8 Reference data memory 10 Noise calculation circuit 11 Correction calculation circuit 13 Heat source rod

Claims (4)

[Claims] 1. A method for removing fixed pattern noise from image data of an infrared sensor (3) in which a plurality of infrared detecting elements are arranged one-dimensionally or two-dimensionally, comprising a heat source of a predetermined temperature in front of the infrared sensor (3). Fixing an infrared sensor characterized by moving a rod (13) and removing fixed pattern noise from image data obtained at the time of imaging based on reference data obtained corresponding to the movement of the heat source rod (13) Pattern noise removal method. 2. An apparatus for removing fixed pattern noise from image data of an infrared sensor (3) in which a plurality of infrared detecting elements are arranged one-dimensionally or two-dimensionally, in a predetermined temperature moving in front of the infrared sensor (3). Heat source rod
(13), a reference data memory (8) for storing the reference data obtained corresponding to the movement of the heat source rod (13), and noise data formed based on the reference data from the image data at the time of imaging. A fixed pattern noise eliminator for an infrared sensor, comprising: a correction calculation circuit (11) for subtracting. 3. The fixed pattern noise elimination device for an infrared sensor according to claim 2, wherein the noise data is the reference data itself. 4. The fixed pattern noise elimination device for an infrared sensor according to claim 2, wherein the noise data is obtained through a noise detection circuit (10) for subtracting an average value of the reference data from the reference data.