CN103308178B - A kind of asymmetric correction method of un-cooled infrared focal plane array - Google Patents

Abstract

The embodiment of the present invention discloses a non-uniformity correction method of an uncooled infrared focal plane array, which includes calculating correction parameters of the infrared focal plane array at at least two calibrated operating temperatures and storing them in a memory; measuring the infrared focal plane The substrate temperature of the array; according to the substrate temperature, the current correction parameter corresponding to the substrate temperature is obtained from the memory; and the infrared image is corrected with the current correction parameter. In the method of the present invention, since the correction parameters of the infrared focal plane array are stored at each calibration working temperature, when the infrared focal plane array is working, it is not necessary to perform a little correction on the infrared focal plane array, and the infrared focal plane array is directly read from the system memory. The correction parameters corresponding to the current working temperature of the focal plane array ensure that the infrared imaging system realizes uninterrupted real-time imaging of infrared targets.

Description

A Non-Uniformity Correction Method for Uncooled Infrared Focal Plane Array

technical field

The invention relates to the field of infrared imaging systems, in particular to a method for correcting non-uniformity of an uncooled infrared focal plane array.

Background technique

Infrared focal plane arrays were developed in the late 1970s and early 1980s, driven by defense applications and other strategic and tactical applications. It is an important optoelectronic device to obtain the infrared thermal radiation information of the scene. Infrared focal plane array is the core component of infrared imaging technology, widely used in military, industrial, agricultural, medical, forest fire prevention and other fields of imaging.

Infrared imaging system is an important part of infrared thermal imaging system. At present, various infrared imaging systems have been widely used in communication, medical, military, industrial and other fields.

Infrared focal plane array belongs to the second-generation infrared imaging device and is the core of modern infrared imaging system. It has the advantages of simple structure, stable operation, small noise equivalent temperature difference, and high sensitivity.

In an infrared system, under ideal conditions, the infrared focal plane array is irradiated uniformly, and the output amplitude should be exactly the same. But in fact, due to the inhomogeneity of semiconductor materials for making devices (impurity concentration, crystal defects, inhomogeneity of internal structure, etc.), mask errors, defects, process conditions and other factors, under the condition of uniform radiation, its output The magnitudes are not the same, which is the non-uniformity of the IRFPA response.

There are many reasons for the infrared non-uniformity, the main one is the non-uniformity of the thermal imaging detector itself, and the external input of the infrared focal plane array will also affect the non-uniformity. For example, the difference in the bias voltage and bias current of the detector will also cause the non-uniformity of the output, which is mainly manifested as fixed additive noise. However, due to limitations of manufacturing materials and manufacturing processes, the response characteristics of each pixel of the infrared focal plane array cannot be completely consistent.

The non-uniformity of the infrared focal plane array will seriously affect the detection sensitivity and spatial resolution of the infrared imaging system. Therefore, it is necessary to perform non-uniformity correction on the infrared focal plane array in practical use.

At present, there are many commonly used infrared non-uniformity correction techniques, such as calibration-based one-point correction, two-point correction non-uniformity algorithm, scene-based time-domain high-pass filter method, adaptive artificial neural network method and mean value filter algorithm, etc. Wait. But at present, no algorithm with strong adaptability has been found, and all kinds of non-uniformity algorithms have their deficiencies.

In the prior art, the one-point calibration algorithm and the two-point calibration algorithm are widely used in practice.

The two-point correction algorithm takes into account the gain non-uniformity and bias non-uniformity of the detector. In general, when the incident infrared radiation is zero, the response output of the detector is not zero. The two-point correction method transforms the response characteristic curves of all detection units into the same response characteristic curve through rotation and translation. After correction, in the case of uniform radiation input, the output electrical signals of each detection unit are the same, thereby eliminating the non-uniform noise of the infrared image. However, the two-point calibration of infrared images requires temperature calibration.

One-point correction algorithm is the earliest non-uniformity correction algorithm. For the two situations of gain coefficient non-uniformity and bias coefficient non-uniformity, one-point correction method can also be divided into two types, which are divided into correction of non-uniform gain coefficient and bias correction. Uneven corrections can be set, but only one correction can be satisfied at a time.

Using bias inhomogeneity correction, the principle of one-point correction is to assume that the output signal of the photosensitive element of the detector is linearly related to the radiant flux of the target, and the one-point correction algorithm is to convert the output signal of each pixel under uniform light radiation The correction is consistent, that is, under a certain light irradiance, the output signals of different pixels are corrected to a certain signal. This signal can be the maximum value or some other value under this condition, and the average value is generally taken.

The essence of one-point correction is only to compensate the dark current of the device, but not to correct the gain.

In the actual work of the focal plane array, there is a nonlinear relationship between the output signal of the photosensitive element of the detector and the radiant flux of the target, and the gain and bias will also change nonlinearly with the change of the ambient temperature, resulting in infrared focus Infrared non-uniformity of planar arrays. The two-point correction method is to divide the working temperature range of the infrared focal plane array into small temperature ranges according to the rising gradient of the temperature. In a small temperature range, it is assumed that the output signal of the photosensitive element of the detector has a linear relationship with the radiant flux of the target, and then the bias parameter in this small temperature range is calculated by using a two-point correction algorithm.

With the demand of the market and the advancement of technology, the infrared imaging system generally adopts the packaging form without TEC at present. In addition to the traditional two-point calibration, the infrared imaging system without the TEC packaging form needs to be corrected in practice. With the use of time and changes in ambient temperature and the temperature of the focal plane array of the infrared imaging system itself, temperature drift will occur. Therefore, frequent shutter corrections are required to eliminate the influence of infrared non-uniformity of the infrared focal plane array.

In a wide temperature range, if a one-point correction algorithm is used to eliminate the infrared non-uniformity of the infrared focal plane array, it is necessary to select a uniform irradiance for the focal plane array of the infrared imaging system during one-point correction. This method makes the infrared imaging During the actual use of the system, the information acquisition of the infrared target by the infrared imaging system must be temporarily interrupted. This frequent shutter correction seriously affects the continuous observation of infrared targets by infrared imaging systems.

Contents of the invention

One of the objects of the present invention is to provide a non-uniformity correction method capable of updating correction parameters of an infrared imaging system without interrupting an uncooled infrared focal plane array of the infrared imaging system.

The technical solutions disclosed in the embodiments of the present invention include:

A method for correcting non-uniformity of an uncooled infrared focal plane array is provided, comprising: step A: calculating correction parameters of the infrared focal plane array at at least two calibrated operating temperatures, and storing the correction parameters In the memory; step B: measure the substrate temperature of the infrared focal plane array; step C: according to the substrate temperature, obtain the current correction parameter corresponding to the substrate temperature from the memory; step D : using the infrared focal plane array to perform infrared imaging on a target object to obtain an infrared image; Step E: correcting the infrared image using the current correction parameters.

Further, the step A includes: placing the infrared imaging system in an incubator; adjusting the temperature of the incubator to the first calibrated working temperature and keeping it at the first calibrated working temperature; The first correction parameter of the infrared focal plane array of the infrared imaging system at the first calibration working temperature; the first correction parameter is stored in the memory; the temperature of the thermostat is adjusted to the second Calibrate the working temperature and keep it at the second calibrated working temperature; use the two-point correction method to calculate the second correction parameter of the infrared focal plane array at the second calibrated working temperature; store the second correction parameter in in the memory.

Further, the step A also includes: adjusting the temperature of the thermostat to the third calibrated working temperature and keeping it at the third calibrated working temperature; Third calibration parameters at the calibrated working temperature; storing the third calibration parameters in the memory.

Further, the step C includes: comparing the substrate temperature with the at least two calibrated operating temperatures, and obtaining the calibrated operating temperature that is equal to the substrate temperature or has the smallest difference with the substrate temperature As the corresponding working temperature; reading the correction parameter at the corresponding working temperature from the memory, and using the correction parameter at the corresponding working temperature as the current correction parameter.

Further, the step C includes: comparing the substrate temperature with the small temperature range to which the at least two calibrated working temperatures belong, and judging the small temperature range to which the substrate temperature belongs; The correction parameter in the small temperature range is the current correction parameter.

Further, the correction parameters include offset parameters and/or gain parameters.

In the method of the embodiment of the present invention, since the correction parameters of the infrared focal plane array are stored at each calibration operating temperature point, when the infrared focal plane array is working, it is not necessary to perform a little correction on the infrared focal plane array, directly from the system memory The correction parameters corresponding to the current working temperature of the infrared focal plane array are read in the middle, thus ensuring the uninterrupted real-time imaging of the infrared target by the infrared imaging system.

Description of drawings

Fig. 1 is a schematic flowchart of a method for correcting non-uniformity of an uncooled infrared focal plane array according to an embodiment of the present invention.

Fig. 2 is a schematic flowchart of the steps of calibrating and storing correction parameters in one embodiment of the present invention.

detailed description

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Fig. 1 is a schematic flowchart of a method for correcting non-uniformity of an uncooled infrared focal plane array according to an embodiment of the present invention. As shown in FIG. 1 , in this embodiment, the non-uniformity correction method of the uncooled infrared focal plane array includes step 10 , step 12 , step 14 and step 16 . Each step in the method will be described in detail below with reference to the accompanying drawings.

Step 10: Calibrate and store the correction parameters.

In the embodiment of the present invention, firstly, the infrared focal plane array of the infrared imaging system is calibrated, the correction parameters of the infrared focal plane array at each calibration working temperature are obtained, and then these correction parameters are stored in the memory of the infrared imaging system, It can be called as needed during the subsequent infrared imaging process. For example, in the subsequent infrared imaging process, when a temperature drift occurs, the current correction parameters at the corresponding working temperature are read from the memory and the infrared image is corrected with the current correction parameters to compensate for the temperature drift.

The working temperature of the infrared focal plane array has a certain range. If each temperature point in the working temperature range is calibrated, the workload will be very large, and the data volume of the correction parameters that needs to be stored will also be very large. Therefore, It is very difficult to calibrate each temperature point.

Therefore, in the embodiment of the present invention, some calibration working temperatures (at least two calibration working temperatures) can be selected for calibration in the working temperature range of the infrared focal plane array, and the following calibration working temperatures (at least two calibration working temperatures) can be obtained. correction parameters.

In some embodiments of the present invention, the working temperature range of the infrared focal plane array can be divided into various small temperature ranges according to the gradient of temperature rise. According to the sensitivity of the temperature sensor of the infrared imaging system and the material properties of the infrared focal plane array, an appropriate temperature range is selected for each small temperature interval. Within the same small temperature interval, the same calibration parameters are used. Different small temperature ranges have different calibration parameters. In this way, for each small temperature interval, it is only necessary to calibrate the correction parameter at one of the temperature points as the correction parameter for the entire small temperature interval. A temperature in the temperature range. Here, the selection of the small temperature range and the selection of the temperature used for calibration in the small temperature range can be flexibly selected according to the actual situation, and the present invention does not make any special limitation.

In these embodiments, the memory of the infrared imaging system correspondingly also stores relevant information of each small temperature region, such as the temperature value of the endpoint of each small temperature interval, and the like.

In some other embodiments of the present invention, the previously selected calibration working temperature for calibration is some temperature points selected according to actual needs in the working temperature range of the infrared focal plane array. For the rest of the temperature points between the two selected calibrated working temperatures, the calibration parameters of the nearest calibrated working temperature can be used. Here, the selection of the calibrated working temperature can be flexibly selected according to the actual situation, and there is no special limitation in the present invention. The spacing between each calibrated operating temperature (i.e. the temperature difference between two calibrated operating temperatures) can be the same (i.e. the selected calibrated operating temperature is uniformly distributed in the operating temperature range of the infrared focal plane array), or it can be different (that is, the selected calibration operating temperature is non-uniformly distributed in the operating temperature range of the infrared focal plane array).

Therefore, in step 10, the correction parameters of the infrared focal plane array at at least two calibrated working temperatures are calculated, and the calculated correction parameters are stored in the memory of the infrared imaging system.

In an embodiment of the present invention, the process of calibrating and storing the correction parameters may be as shown in FIG. 2 .

First, in step 101, the infrared imaging system is placed in an incubator, that is, the calibration process of the infrared focal plane array of the infrared imaging system will be performed in the incubator.

Then, in step 102, adjust the temperature of the thermostat, adjust the temperature of the thermostat to a calibrated working temperature, and keep it at the calibrated working temperature.

Subsequently, in step 106, the correction parameters of the infrared focal plane array at the current calibrated working temperature are calculated. Here, any suitable method can be used for the method of calculating the correction parameters of the infrared focal plane array at a certain temperature, for example, a two-point correction method can be used. These methods may be methods commonly used in the art, and will not be described in detail here.

Then, the correction parameters at the calibrated working temperature calculated and obtained in step 106 are stored in the memory of the infrared imaging system. The calculated correction parameters can be stored in any suitable memory in the infrared imaging system.

In this way, the calibration and storage of the calibration parameters at a calibration working temperature are completed.

After the calibration and storage of the correction parameters at this one calibration working temperature is completed, in step 110, it is judged whether all calibration working temperatures that need to be calibrated have been calibrated. Here, as mentioned above, the calibration working temperature that needs to be calibrated can be flexibly selected according to the actual situation.

If it is judged in step 110 that all the calibration working temperatures that need to be calibrated have not been calibrated, then adjust the temperature of the thermostat to the next calibration working temperature, and keep it at this calibration working temperature, then perform above-mentioned steps 106, 108 and 110.

If it is determined in step 110 that all calibration working temperatures that need to be calibrated have been calibrated, the step of calibrating and storing the correction parameters (ie, step 10 ) ends.

For example, in one embodiment, step 10 may include the following steps:

Place the infrared imaging system in an incubator;

Adjust the temperature of the thermostat to the first calibrated working temperature and keep it at the first calibrated working temperature;

Calculating the first correction parameter of the infrared focal plane array of the infrared imaging system at the first calibration working temperature by using a two-point correction method;

storing the first correction parameter in memory;

Adjust the temperature of the thermostat to the second calibrated working temperature and keep it at the second calibrated working temperature;

Using the two-point correction method to calculate the second correction parameter of the infrared focal plane array at the second calibration working temperature;

The second correction parameters are stored in memory.

In the above embodiment, it may also include:

Adjust the temperature of the thermostat to the third calibrated working temperature and keep it at the third calibrated working temperature;

Using the two-point correction method to calculate the third correction parameter of the infrared focal plane array at the third calibration working temperature;

A third correction parameter is stored in memory.

It is easy to understand that, similarly, the above-mentioned embodiments may also include similar steps at the fourth, fifth, sixth and so on.

In the embodiment of the present invention, when storing the calculated correction parameters at each calibrated working temperature, it may be stored in any suitable manner or data structure. For example, the memory can be divided into multiple storage spaces according to the selected calibrated working temperature, and each storage space is selected according to the specification of the infrared focal plane array. The appropriate size, each storage space corresponds to a calibrated working temperature of the infrared focal plane array , and store the correction calculated according to the preceding steps at the corresponding calibrated working temperature, and in a storage space, the correction parameters can be stored sequentially according to the distribution of the pixel positions of the infrared focal plane array.

In the embodiment of the present invention, the aforementioned correction parameters may be any parameters suitable for correcting the non-uniformity of the infrared focal plane array of the infrared imaging system. For example, in an embodiment, the correction parameter here may be an offset parameter and/or a gain parameter. The concept of the offset parameter and/or the gain parameter is a commonly used concept in non-uniformity correction in the art, and will not be described in detail here.

Step 12: Measure the substrate temperature of the infrared focal plane array.

The substrate temperature of the infrared focal plane array indicates the current operating temperature of the infrared focal plane array. In an embodiment of the present invention, in step 12, the substrate temperature of the infrared focal plane array is measured. This measurement can be achieved with a temperature sensor. The temperature sensor converts the temperature of the substrate of the infrared focal plane array into an electrical signal, and after analog-to-digital conversion, converts it into a digital signal, and then sends it to the controller of the infrared imaging system.

For example, in one embodiment, the temperature sensor may include a thermistor. The resistance value of the thermistor can change with the change of temperature. When the substrate temperature of the infrared focal plane array changes, the resistance value of the thermistor also changes accordingly, so that the voltage VTEMP output by the temperature sensor changes. The linear relationship between VTEMP and the substrate temperature of the infrared focal plane array:

VTEMP=A×T+B.

Among them, T is the substrate temperature of the infrared focal plane array, and A and B are constant coefficients, which are determined by the characteristics of the temperature sensor of the infrared imaging system.

Step 14: Obtain the current calibration parameters corresponding to the substrate temperature.

After the substrate temperature is obtained by measurement, the current calibration parameters of the infrared focal plane array corresponding to the substrate temperature can be obtained from the aforementioned memory according to the substrate temperature.

As mentioned above, in some embodiments, multiple correction parameters at the calibrated working temperature are stored in the memory, and each correction parameter at the calibrated working temperature is a correction parameter of the infrared focal plane array in a small temperature range. Therefore, in step 14, after the substrate temperature is obtained, it is judged which small temperature range the substrate temperature belongs to, and then the correction parameter of the small temperature range it belongs to is used as the current correction parameter corresponding to the substrate temperature. Here, the current calibration parameter "corresponding" to the substrate temperature refers to the current calibration parameter of the infrared focal plane array at the substrate temperature.

For example, in these embodiments, it may be determined which small temperature interval the substrate temperature belongs to by comparing the substrate temperature with the temperature values at the endpoints of each small temperature interval stored in the memory of the infrared imaging system.

As mentioned above, the correction parameters of each small temperature interval have been calibrated and stored in step 10. Therefore, at this time, after judging which small temperature interval the measured substrate temperature belongs to, it can be directly read from the memory. The correction parameters of the small temperature range to which it belongs.

Or, as mentioned above, in some other embodiments, the memory stores the correction parameters at multiple calibration working temperatures, and the calibration parameters at the remaining temperature points between the two calibration working temperatures can use the calibration work closest to it. Correction parameter for temperature. Therefore, at this time, the substrate temperature can be compared with at least two calibrated operating temperatures in step 10, and the calibrated operating temperature that is equal to the substrate temperature or has the smallest difference with the substrate temperature is obtained as the corresponding operating temperature; The correction parameter at the corresponding working temperature is read from the memory, and the correction parameter at the corresponding working temperature is used as the current correction parameter.

Step 16: Infrared imaging Obtain an infrared image, and correct the infrared image with the current correction parameters.

After obtaining the current calibration parameters at the current substrate temperature, use the infrared imaging system (or infrared focal plane array) to perform normal infrared imaging on the target object to obtain an infrared image. The specific steps of using an infrared imaging system or an infrared focal plane array to perform infrared imaging on a target object to obtain an infrared image may be the same as commonly used steps in the art, and will not be described in detail here.

After the infrared image is obtained, the current correction parameters obtained in step 14 can be used to correct the obtained infrared image.

For example, in one embodiment, the current correction parameters include the current offset parameter O and the current gain parameter G, then the formula V'(i,j)=G(i,j)×V(i,j)+O( i, j) Calculate the correction result and generate the corrected infrared image. Where V'(i,j) is the voltage value at the pixel point (i,j) in the corrected infrared image, and V(i,j) is the voltage value at the pixel point (i,j) in the infrared image before correction , G(i,j) is the value of the current gain parameter at the pixel point (i,j), O(i,j) is the value of the current bias parameter at the pixel point (i,j), where (i, j) refers to the pixels in the infrared focal plane array, where i is a natural number less than or equal to the number of rows of the infrared focal plane array, and j is a natural number less than or equal to the number of columns of the infrared focal plane array.

In this way, in the embodiment of the present invention, during the normal infrared imaging process, the substrate temperature of the infrared focal plane array can be monitored in real time, and the corresponding correction parameters can be read from the memory according to the substrate temperature in real time and corrected. The resulting infrared image is corrected for non-uniformity.

The methods in the embodiments of the present invention can be implemented by any suitable software or hardware. For example, in one embodiment, it can be implemented with an FPGA correction circuit, and the FPGA correction circuit has the advantages of simple design and easy implementation.

For example, the correction parameters of the infrared focal plane array at each calibrated working temperature are sequentially stored in the FLASH chip according to the increment of the calibrated working temperature and the increment of the number of pixels of the infrared focal plane array. When the infrared imaging system is working, the temperature sensor of the infrared imaging system collects the temperature information of the infrared focal plane array substrate, converts it into an output voltage, and inputs it to the FPGA after the digital-to-analog conversion is completed by the A/D conversion device. Corresponding calibration parameters. The infrared target object is identified by the infrared imaging system. The infrared imaging system collects and outputs relevant information. The output information is sent to the A/D conversion device after signal enhancement. After the digital-to-analog conversion is completed, it is input to the FPGA. After the enhancement, the data is converted into an analog signal through the D/A conversion device and then input to the terminal display device through the amplifier.

In the embodiment of the present invention, for the problem of selecting irradiance and recalculating the correction parameters when one point is corrected, the correction parameters of the infrared focal plane array at each calibration working temperature are stored in the system memory, when the infrared focal plane array When temperature drift occurs during work, the correction parameters corresponding to the current working temperature of the infrared focal plane array are read from the system memory, and then the read correction parameters are used to correct and compensate for temperature drift.

The infrared focal plane array needs to select the irradiance again when performing a point correction, which will temporarily interrupt the imaging of the infrared target by the infrared imaging system, and in the method of the present invention, since the infrared focal plane array is stored at each calibration working temperature Correction parameters, when the infrared focal plane array is working, there is no need to correct the infrared focal plane array, and the correction parameters corresponding to the current operating temperature of the infrared focal plane array are directly read from the system memory, thus ensuring the realization of the infrared imaging system Uninterrupted real-time imaging of infrared targets.

The present invention has been described above through specific examples, but the present invention is not limited to these specific examples. Those skilled in the art should understand that various modifications, equivalent replacements, changes, etc. can also be made to the present invention. As long as these changes do not deviate from the spirit of the present invention, they should all be within the protection scope of the present invention. In addition, "one embodiment" described in many places above represents different embodiments, and of course all or part of them may be combined in one embodiment.

Claims (4)

1. A non-uniformity correction method for an uncooled infrared focal plane array, characterized in that it comprises: Step A: Calculating correction parameters of the infrared focal plane array at at least two calibrated operating temperatures, and storing the correction parameters in a memory; Step B: measuring the substrate temperature of the infrared focal plane array; Step C: According to the substrate temperature, obtain the current correction parameter corresponding to the substrate temperature from the memory; Step D: using the infrared focal plane array to perform infrared imaging on the target object to obtain an infrared image; Step E: Correcting the infrared image with the current correction parameters; Wherein, the step C includes: Comparing the substrate temperature with the small temperature range to which the at least two calibrated working temperatures belong, and judging the small temperature range to which the substrate temperature belongs; The correction parameter of the small temperature interval to which the substrate temperature belongs is used as the current correction parameter. 2. The method according to claim 1, wherein said step A comprises: Place the infrared imaging system in an incubator; adjusting the temperature of the thermostat to a first calibrated working temperature and maintaining it at the first calibrated working temperature; Using a two-point calibration method to calculate a first calibration parameter of the infrared focal plane array of the infrared imaging system at the first calibration working temperature; storing said first correction parameter in said memory; adjusting the temperature of the thermostat to a second calibrated operating temperature and maintaining it at the second calibrated operating temperature; Using a two-point calibration method to calculate a second calibration parameter of the infrared focal plane array at the second calibration working temperature; The second correction parameter is stored in the memory. 3. The method according to claim 2, wherein said step A further comprises: adjusting the temperature of the thermostat to a third calibrated working temperature and maintaining it at the third calibrated working temperature; Using a two-point calibration method to calculate a third calibration parameter of the infrared focal plane array at the third calibration working temperature; The third correction parameter is stored in the memory. 4. The method according to claim 1, wherein the correction parameters include offset parameters and/or gain parameters.