Method for adjusting, in particular operationally, a detection system, in particular by uncooled infrared imaging, and associated adjustment device.

Abstract

This method for adjusting a detection system (2) forming a succession of images of a scene (4), the detection system (2) comprising a sensor (6) provided with a matrix of active detectors (8), a plurality of blind detectors (10), as well as a reading circuit (12) providing a response signal for each sensitive detector (8), comprises the calculation of a value representative of at least part of the response signals, the determination of a deviation between said representative value and a target value, the comparison of the deviation with a tolerance threshold, and according to the result of the comparison, the modification of a basing voltage in order to reduce the deviation. Figure for the abstract: Fig 2

Description

Title of the invention: Method for adjusting, in particular operationally, a detection system, in particular by uncooled infrared imaging, and associated adjustment device. Technical field

[0001] The technical field of the invention is electromagnetic radiation detection systems, in particular bolometric detection systems for uncooled infrared imaging.

[0002] In particular, the present invention relates to a method for adjusting, in particular operationally, a detection system and an associated adjustment device. Prior techniques

[0003] The temperature of an object is characteristic of its spectral emission. The analysis of the electromagnetic radiation coming from a scene containing the object can make it possible to detect the object and to characterize its nature. There are applications for detection and / or monitoring and / or optical surveillance of the scene requiring the distinction of objects of similar temperatures and / or requiring the detection of the temperature of objects over a wide temperature range with the same detection system.

[0004] The detection system generally comprises an array of bolometric detectors sensitive to electromagnetic radiation coming from the scene, as well as a plurality of blind bolometers insensitive to said electromagnetic radiation.

[0005] The resistance of the bolometric detectors of the matrix depends on the temperature of the scene and the temperature of the components of the detection system. The resistance of the blind bolometers does not depend on the temperature of the scene and depends on the temperature of the components of the detection system.

[0006] The detection system also comprises an analog-digital converter and a computer provided with a memory in which are recorded a setting value of the polarization voltage of the matrix of bolometric detectors, a setting value of the polarization voltage of the blind bolometers and a setting value of a trans-impedance capacitive amplification gain, called "CTIA gain".

[0007] The detection system provides a succession of images of the scene from measurements of the bolometric detector matrix, measurements of the blind bolometers and the CTIA gain.

[0008] The adjustment values ​​of the detection system are sometimes unsuitable for the conditions of implementation of the detection system, harming the quality of the images of the scene formed, and therefore the quality of the information acquired on the object to be detected.

[0009] The measurement noise of the detection system may be too high relative to the object to be detected.

[0010] The object to be detected can saturate the images of the scene, in particular by being too hot or too cold compared to the scene.

[0011] Furthermore, the adjustment values ​​of the detection system are generally defined in the factory at the start of the life of the detection system and therefore do not take into account the aging of the detection system and its electronics. Statement of the invention

[0012] The present invention therefore aims to overcome all or part of the aforementioned drawbacks, to reduce measurement noise of a detection system observing a scene, to increase the precision of discrimination of objects of close temperature in the scene, to allow the detection of the temperature of objects over a wide temperature range, to increase a measurement dynamic of the detection system with respect to the observed scene, to improve the robustness of the detection system to aging, to heating of the components of the detection system and to variations in the observed scene.

[0013] The present invention relates to a method for adjusting a detection system forming a succession of images of a scene, the detection system comprising a sensor provided with a matrix of detectors sensitive to electromagnetic radiation coming from the scene, called "active", a plurality of detectors insensitive to said radiation, called "blind", as well as a reading circuit providing a response signal for each sensitive detector, the method comprising:

[0014] - the calculation of a value representative of the level of at least part of the signals of response;

[0015] - determining a difference between said representative value and a target value;

[0016] - comparing the deviation to a tolerance threshold; and

[0017] - according to the result of the comparison, the modification of a bias voltage applied to insensitive detectors called “base voltage”, in order to reduce the gap.

[0018] All of the response signals from the sensitive detectors form a video stream comprising the succession of images of the scene.

[0019] The calculation of the value representative of the level of at least a part of the response signals may comprise one of: the calculation of an instantaneous or temporal average value of at least a part of the response signals, the calculation of a value instantaneous or temporal median of at least part of the response signals or the calculation of another statistical function applied to at least part of the response signals.

[0020] Determining said deviation, comparing said deviation with the tolerance threshold and modifying the base voltage in order to reduce said deviation make it possible to control said representative value to the target value by adapting the base voltage.

[0021] Modifying the basing voltage as a function of the difference between the value representative of the level of at least part of the response signals and the target value makes it possible to reduce the risk of saturation of objects present in the scene in the image of the scene, in particular of objects whose temperature is far from the average temperature of the observed scene.

[0022] Adapting the base voltage to the measurement made by the sensor of the detection system makes it possible to adapt the dynamics of the sensor with respect to the scene observed during the implementation of the system, to make the system less sensitive to the aging of the components of the system, in particular less sensitive to the aging of the sensor, and to make the system robust to variations in the temperature of implementation of the system.

[0023] Calculating a value representative of the level of at least a portion of the response signals may comprise calculating a voltage representative of voltage values ​​provided by the detection system for each active detector or calculating an intensity representative of intensity values ​​of the pixels of an image of the scene formed by the detection system.

[0024] The target value may correspond to a value between a minimum analog-to-digital conversion voltage value of the detection system and a maximum analog-to-digital conversion voltage value of the detection system.

[0025] The target value may correspond to a value close to the middle of the analog-to-digital conversion range of the detection system. For example, the target value may be between 0.9 and 1.1 times a value corresponding to the middle of the analog-to-digital conversion range of the detection system.

[0026] The choice of correspondence to a value close to the middle of the conversion range makes it possible to have a similar margin between the minimum value of analog-digital conversion voltage of the system and the target value and between the maximum value of analog-digital conversion voltage of the system and the target value. Thus, the risk of saturation of so-called "hot" objects is similar to the risk of saturation of so-called "cold" objects, the choice of the target value taking into account the variation in luminance of the electromagnetic radiation of a black body as a function of the temperature of the black body.

[0027] Advantageously, the target value is different from the value corresponding to the middle of the conversion range so as to increase the dynamics of the sensor towards high temperatures.

[0028] Said target value can be corrected according to an estimated operational measurement need in particular in order to correspond to a non-central value of the analog-digital conversion range of the detection system.

[0029] The estimated operational measurement need corresponds to a need to measure the temperature of objects whose temperature is far from the average temperature of the scene. For example, when the estimated operational measurement need corresponds to a need to measure the temperature of objects whose temperature is higher than the average temperature of the scene, said target value may be increased or decreased in order to reduce the risk of saturation of said objects in the image of the scene.

[0030] The value of the modification of the basing voltage can be selected, at least as a function of said difference, in a previously determined table of correspondence between a variation of the basing voltage and a variation of the value representative of the level of at least a part of the response signals.

[0031] Thus, the modification of the basing voltage is based on a previously determined value of correspondence between the variation of the basing voltage and the variation of the value representative of the level of at least part of the response signals.

[0032] Said correspondence table allows accelerated convergence of the deviation towards a value lower than the tolerance threshold.

[0033] Said correspondence table is representative of a law of variation of the value representative of the level of at least part of the response signals as a function of the value of the basing voltage.

[0034] The modification of the basing voltage can also be selected from said correspondence table as a function of a current bias voltage of the matrix of active detectors of the sensor and / or as a function of a current value of trans-impedance capacitive amplification gain of the sensor and / or as a function of the temperature of the detection system.

[0035] Said current values ​​correspond to the values ​​applied to the sensor of the detection system before the modification of the base voltage.

[0036] Said correspondence table can be established in the factory.

[0037] Said correspondence table can also be established for several values of the bias voltage of the active detector array of the sensor and / or for several values ​​of trans-impedance capacitive amplification gain of the sensor and / or for several temperatures of the detection system.

[0038] Thus, said correspondence table is established for several implementation parameters of the detection system, and allows accelerated convergence of the deviation towards a value lower than the tolerance threshold.

[0039] The modification of the basing voltage can be carried out between two successive image acquisitions of the detection system.

[0040] Thus, the appearance of an intensity gradient on the image of the observed scene is avoided, the intensity gradient corresponding to a sequential application, for example in the case of a “rolling shutter” type implementation in Anglo-Saxon terms of the detection system, of the basing voltage to a plurality of blind detectors arranged by rows or by columns of the matrix of active detectors.

[0041] The method may comprise an initialization of the detection system during which a bias voltage value of the active detectors and / or a bias voltage value of the blind detectors and / or a trans-impedance capacitive amplification gain value of the sensor is selected at least as a function of a measurement of the temperature of the system.

[0042] The initialization of the system corresponds, for example, to a power-up of the system.

[0043] The bias voltage value of the active detectors and / or the bias voltage value of the blind detectors and / or the trans-impedance capacitive amplification gain value of the sensor may be selected from a predetermined table of values ​​or be selected according to a predetermined function.

[0044] During system initialization, a current sensor gain non-uniformity correction table may also be selected at least as a function of the system temperature measurement.

[0045] During system initialization, a current sensor additive non-uniformity correction table, also called an "offset" non-uniformity correction table, may also be selected at least as a function of the system temperature measurement.

[0046] The bias voltage value of the active detectors is selected as a function of the measured temperature of the system to improve a signal-to-noise ratio of the detection system by reducing a noise of the sensor, in particular a temporal noise of the sensor corresponding to the variations of the response signals of the sensitive detectors when the detection system observes a fixed scene of constant temperature.

[0047] Improving the signal-to-noise ratio of the detection system is carried out with the constraint of encompassing, or at least matching, the estimated operational measurement requirement to the dynamics of the sensor. Thus, the bias voltage value of the active detectors selected as a function of the temperature measured system temperature allows the system to be implemented over a wide range of detection system temperatures.

[0048] The bias voltage value of the blind detectors selected as a function of the measured temperature of the system allows accelerated convergence of the deviation towards a value lower than the tolerance threshold, the current bias voltage of the blind detectors then being adapted to the temperature of the system. Indeed, when the bias voltage value of the blind detectors is not selected as a function of the temperature, the image of the scene could be completely saturated during the calculation of the value representative of the level of at least part of the response signals, then slowing down the control of said representative value to the target value by adapting the basing voltage.

[0049] The trans-impedance capacitive amplification gain value of the sensor selected as a function of the measured system temperature allows the use of a higher trans-impedance capacitive amplification gain value of the sensor at low temperature than at high temperature to reduce the impact of analog-to-digital conversion noise of the system.

[0050] The bias voltage value of the active detectors and / or the bias voltage value of the blind detectors and / or the trans-impedance capacitive amplification gain value of the sensor may also be selected depending on the estimated operational measurement need.

[0051] The values ​​contained in said previously determined table of values ​​can be established for several temperatures of the detection system and by the use of several reference scenes in order to encompass, or at least to match, the estimated operational measurement need to the dynamics of the sensor.

[0052] Said previously determined table of values ​​can be established by the use of a reference scene per temperature of the detection system, for example a scene of constant temperature in particular equal to the temperature of the detection system, or can be established by the use of several reference scenes per temperature of the detection system, for example for several reference scenes at different temperatures.

[0053] The method may comprise, following the modification of the base voltage, in particular when said deviation is less than the tolerance threshold, the application of a correction table for the non-uniformities in additive of the sensor adapted to the modification of the base voltage.

[0054] The correction table for non-uniformities in additive of the sensor adapted to the modification of the basing voltage can be equal to a current correction table for non-uniformities in additive of the sensor to which a term equal to the variation of the intensity level of the pixels of the images of the scene following the modification of the base voltage multiplied by a table of correction of non-uniformities in gains.

[0055] The sensor's additive non-uniformity correction table can be updated using a decolumnizing and / or delineating algorithm.

[0056] The sensor additive non-uniformity correction table is thus adapted to the modified basing voltage. Preferably, the sensor additive non-uniformity correction table is also adapted to the current bias voltage of the active detectors and to the current transimpedance capacitive amplification gain value of the sensor. Indeed, the current sensor additive non-uniformity correction table, applied to the images of the scene before the basing voltage is modified, is no longer adapted to the new basing voltage.

[0057] The present invention also relates to an adjustment device for a detection system forming a succession of images of a scene, the detection system comprising a sensor provided with a matrix of detectors sensitive to electromagnetic radiation coming from the scene, called "active", a plurality of detectors insensitive to said radiation, called "blind", as well as a reading circuit providing a response signal for each sensitive detector, the device comprising: - a means for calculating a value representative of the level of at least part of the response signals; - a means of determining a deviation between said representative value and a target value; and - a means of comparing the deviation to a tolerance threshold; - a means of modifying a bias voltage applied to the insensitive detectors, called “base voltage”.

[0058] The device may include a temperature sensor configured to measure the temperature of the detection system and / or the sensor of the detection system.

[0059] The device may comprise means for initializing a bias voltage value of the active detectors as a function of the temperature measured by the temperature sensor.

[0060] The device may comprise means for initializing a bias voltage value of the blind detectors as a function of the temperature measured by the temperature sensor.

[0061] The device may comprise means for initializing a trans-impedance capacitive amplification gain value of the sensor as a function of the temperature measured by the temperature sensor.

[0062] The device may comprise means for selecting an estimated operational measurement requirement.

[0063] The device may comprise a means for applying a correction table for the non-uniformities of the sensor, in particular in gain and additive. Said application means may be configured to estimate a correction table for the non-uniformities in additive of the sensor. Brief description of the drawings

[0064] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example and made with reference to the appended drawings in which:

[0065] [Fig.l] schematically illustrates a detection system comprising an adjustment device according to the invention;

[0066] [Fig.2] schematically illustrates an adjustment method according to the invention; and

[0067] [Fig.3] schematically illustrates the preliminary determination of tables of values ​​according to the adjustment process. Detailed description

[0068] [Fig.l] schematically represents a detection system 2 observing a scene 4, for example an uncooled infrared detection system, also called an IRNR detector.

[0069] The detection system 2 may be a monitoring and / or surveillance system.

[0070] The detection system 2 comprises an optical sensor 6 provided with a matrix of detectors 8 sensitive to electromagnetic radiation coming from the scene 4, called “active” detectors 8, for example a matrix of bolometric detectors. The sensor 6 also comprises a plurality of detectors 10 insensitive to electromagnetic radiation coming from the scene 4, called “blind” detectors 10, and a reading circuit 12 providing a response signal for each sensitive detector of the sensor 6.

[0071] The detection system 2 provides, from the response signals of the active detectors 8, a succession of images of the scene 4 forming a video stream of the scene 4.

[0072] Electromagnetic radiation includes in particular infrared, even visible, terahertz or ultraviolet radiation.

[0073] The detection system 2 comprises an arrangement 14 of optical components making it possible to project the image of the scene 4 onto the matrix of active detectors 8 located in the focal plane of the arrangement 14 of optical components. Such a detection system 2 is known as a “focal-plane array” (FPA) in English terms.

[0074] Each active detector 8 comprises a thermal resistor sensitive to the electromagnetic radiation of the scene 4. A current passing through the resistor thermal of each active detector 8 is representative of the heating of said active detector 8 linked to the electromagnetic radiation of the scene 4.

[0075] Each blind detector 10 is a detector insensitive, or almost insensitive, to the radiation from the scene 4, generating a current, called compensation, representative of the non-useful current notably linked to the heating of the elements of the detection system 2.

[0076] The blind detectors 10 are arranged so that several blind detectors 10 are associated with a row or a column of the active detector matrix 8.

[0077] The difference between the current flowing through the thermal resistance of each active detector 8 and the compensation current produced by the blind detectors 10 is calculated in order to extract a useful analog signal from the scene 4.

[0078] This current difference is then integrated, in particular by filling a capacitor, over a duration called “integration time”, thus generating a voltage constituting a useful integrated analog signal associated with each active detector 8.

[0079] The reading circuit 12 of the sensor 6 makes it possible to multiplex and sequentially supply the integrated useful analog signals associated with each active detector 8 of the matrix.

[0080] The reading circuit 12 comprises a trans-impedance capacitive amplifier making it possible to apply a trans-impedance capacitive amplification gain of the sensor 6, called “CTIA gain”, to the integrated useful analog signals.

[0081] The detection system 2 comprises implementation electronics (not shown), called “proximity electronics”, provided with at least one analog-digital converter configured to digitally convert the integrated useful analog signals to which the CTIA gain is applied in order to form the images of the scene 4, the images therefore being formed from the signals of the active detectors 8.

[0082] The CTIA gain makes it possible in particular to reduce the contribution of digital conversion noise.

[0083] The proximity electronics is capable of polarizing the active detectors 8 by providing a polarization voltage for the active detectors 8. The proximity electronics is capable of polarizing the blind detectors 10 by providing a polarization voltage for the blind detectors 10, called a “base voltage”.

[0084] The detection system 2 comprises an adjustment device 16 comprising a temperature sensor 18 capable of measuring the temperature of the detection system 2 or of the sensor 6 of the detection system 2. For example, the temperature sensor 18 is integrated into the sensor 6 of the detection system 2.

[0085] The adjustment device 16 comprises a calculator 20 provided with a memory.

[0086] The adjustment device 16 also comprises a means 22 for calculating a value representative of the level of at least a portion of the response signals, a means 24 for determining a difference between the value representative of the level of at least a portion of the response signals and a target value, a means 26 for comparing the difference to a tolerance threshold, a means 28 for modifying the basing voltage, a means 30 for initializing the bias voltage value of the active detectors 8 as a function of the temperature measured by the temperature sensor 18, a means 32 for initializing the basing voltage value as a function of the temperature measured by the temperature sensor 18, a means 34 for initializing the CTIA gain value as a function of the temperature measured by the temperature sensor 18,a means 36 for selecting an estimated operational measurement requirement and a means 38 for applying a table for correcting gain non-uniformities and a table for correcting additive non-uniformities of the sensor 6.,

[0087] For example, the calculator 20 of the adjustment device 16 comprises modules in the form of calculation codes, in particular a module for calculating a value representative of the level of at least a portion of the response signals, a module for determining a difference between the value representative of the level of at least a portion of the response signals and a target value, a module for comparing the difference to a tolerance threshold, a module for modifying the basing voltage, a module for initializing the bias voltage value of the active detectors 8 as a function of the temperature measured by the temperature sensor 18, a module for initializing the basing voltage value as a function of the temperature measured by the temperature sensor 18, a module for initializing the CTIA gain value as a function of the temperature measured by the temperature sensor 18,a module for selecting the estimated operational measurement requirement and a module for applying the correction tables for non-uniformities in gains and additive of the sensor 6.,

[0088] The memory comprises a previously determined correspondence table between a variation in the basing voltage and a variation in the value representative of at least a portion of the response signals, a previously determined table of polarization voltage values ​​of the active detectors 8, a previously determined table of basing voltage values, a previously determined table of CTIA gain values ​​and previously determined tables for correcting the gain and additive non-uniformities of the sensor 6. As a variant, said tables can be established in the form of functions.

[0089] Said previously determined tables of the memory are determined before the operational implementation of the detection system 2, in particular in the factory. The computer 20 comprises program code instructions for implementing a method for adjusting the detection system 2.

[0090] [Fig.2] schematically represents the method of adjusting the detection system 2, the method corresponding in particular to the initialization and operational implementation of the detection system 2.

[0091] Optionally, the method of adjusting the detection system 2 begins with a step 40 of initializing the detection system 2. The initialization step 40 is carried out when the detection system 2 is powered up or regularly so that the detection system 2 adapts to the heating of the components of the detection system 2 and to the variations of the observed scene 4.

[0092] For example, the temperature of the detection system 2 or of the sensor 6 of the detection system 2 is measured with the temperature sensor 18, then implementation parameters of the detection system 2 are selected as a function of the measured temperature, then the implementation parameters are applied.

[0093] For example, it is estimated that the average temperature of the observed scene 4 is close to the temperature of the detection system 2 during its initialization.

[0094] Advantageously, the implementation parameters of the detection system 2 are also selected according to the estimated operational measurement requirement. The estimated operational measurement requirement corresponds to an estimated requirement to measure objects whose temperature is far from the temperature of the detection system 2 during its initialization. The requirement can be estimated manually by an operator using the means 36 for selecting an operational measurement requirement or fixed by design of the detection system 2.

[0095] For this, a current CTIA gain value is selected. For example, the CTIA gain value initialization means 34 selects from the previously determined CTIA gain value table a CTIA gain value adapted to the measured temperature and the operational measurement requirement to reduce the digital conversion noise.

[0096] Then, a current value of bias voltage of the active detectors 8 is selected. For example, the initialization means 30 of the bias voltage value of the active detectors 8 makes a selection from the previously determined table of bias voltage values ​​of the active detectors 8 of a bias voltage value of the active detectors 8 adapted to the measured temperature and to the operational measurement requirement to reduce the measurement noise of the detection system 2, in particular the temporal noise of the sensor 6 corresponding to the variations of the response signals of the active detectors 8 when the detection system 2 observes a fixed scene. This measurement noise corresponds to the NETD, for “noise equivalent temperature difference”, in English terms.

[0097] Then, a current table for correcting the non-uniformities in the gains of the sensor 6 is selected, also called “gain non-uniformity correction” in terms Anglo-Saxon. For example, the application means 38 of a table for correcting the non-uniformities of the sensor 6 makes a selection from the previously determined tables for correcting the non-uniformities of the sensor 6 of a table for correcting the non-uniformities in gains of the sensor 6 adapted to the measured temperature, and advantageously adapted to the current value of the polarization voltage of the active detectors 8 and to the current value of CTIA gain.

[0098] Then, a current value of the base voltage is selected. For example, the initialization means 32 of the base voltage value makes a selection from the previously determined table of base voltage values ​​of a base voltage value adapted to the measured temperature and to the operational measurement requirement.

[0099] Alternatively, the order of selection of the current CTIA gain value, the current bias voltage value of the active detectors 8, the current table for correcting the gain non-uniformities of the sensor 6 and the current basing voltage value may be different.

[0100] A step 42 of acquiring images of the scene 4 is then carried out during which the detection system 2 provides, from the response signals of the active detectors 8, a succession of images of the scene 4.

[0101] Then, a step 44 of controlling the basing voltage is carried out in order to adapt the measurement of the detection system 2 to the observed scene 4 containing, for example, hot and / or cold moving objects.

[0102] We begin by calculating a value representative of all or part of the response signals of the active detectors 8. For example, the representative value is calculated by the calculation means 22 of the detection system 2.

[0103] A difference is determined between the representative value of all or part of the response signals of the active detectors 8 and a target value. For example, the difference is calculated by the determination means 24 of the detection system 2.

[0104] The deviation is compared to a tolerance threshold. For example, the comparison is carried out by the comparison means 26 of the detection system 2.

[0105] If the deviation is greater than the tolerance threshold, the base voltage is modified to reduce the deviation. For example, the base voltage is modified by the modification means 28 of the detection system 2.

[0106] The target value corresponds, for example, to a voltage value between a minimum analog-digital conversion voltage value of the detection system 2 and a maximum analog-digital conversion voltage value of the detection system 2.

[0107] More precisely, the target value corresponds, for example, to a value close to the middle of the analog-digital conversion range of the detection system 2, advantageously offset more towards low scene temperatures than towards high temperatures, in order to meet the dynamic requirements of the sensor 6 with respect to the scene towards high and low temperatures.

[0108] For example, in the factory and for a temperature of the detection system 2 of +20°C, a minimum temperature to be detected of 0°C and a maximum temperature to be detected of +40°C are estimated, an object at the minimum temperature or at the maximum temperature to be detected not having to saturate the image of the scene 4 provided by the detection system 2. The current value of the bias voltage of the active detectors 8 and the current value of the CTIA gain make it possible to include, or at least to match, the total dynamic temperature of the scene 4, namely a temperature variation between the minimum value to be detected and the maximum value to be detected, here a total dynamic temperature of the scene 4 of 40°C, in the dynamic of the sensor 6, namely the voltage interval taken between the minimum value of the analog-digital conversion voltage of the system 2 and the maximum value of the analog-digital conversion voltage of the system 2.In addition, a target value close to the middle of the analog-to-digital conversion range of the detection system 2 makes it possible to avoid non-linear conversion phenomena for values ​​close to the minimum and maximum analog-to-digital conversion voltage values ​​of the detection system 2.

[0109] For example, the minimum analog-to-digital conversion voltage value of system 2 is 0V, the maximum analog-to-digital conversion voltage value of system 2 is 2V, and the average temperature of the observed scene 4 is +20°C. If the representative value calculated for an image of scene 4 is 2V, objects above +20°C in scene 4 are saturated in the images of scene 4. If the tolerance threshold is 0.1V and the target level is IV, then the deviation exceeds the threshold. The basing voltage is therefore modified so that the representative value calculated for the next images of scene 4 approaches 1.0V.

[0110] Alternatively, the control described here as being carried out on a voltage value, can be carried out on a value in digital level (“digital level” in Anglo-Saxon terms) or in any other quantity representative of the level of at least part of the response signals, for example in least significant bit, or “LSB” in Anglo-Saxon terms. Advantageously, the target value is corrected according to the estimated operational measurement requirement.

[0111] For example, it is estimated that warmer objects may need to be measured, for example at +60°C. The target value is then modified so that the target value is significantly different from the average of the minimum analog-to-digital conversion voltage value of system 2 and the maximum voltage value of System 2 analog-to-digital conversion to reduce the risk of saturation of hotter objects.

[0112] The calculation of the representative value of at least part of the response signals can be carried out directly by calculating the average intensity level of all or part of an image of the scene 4 provided by the detection system 2, each pixel of the image of the scene 4 corresponding to a response signal from an active detector 8.

[0113] Step 44 of controlling the basing voltage makes it possible to control the representative intensity level of the images of scene 4 so as to reduce the risk of saturation of hot and cold objects in the images of scene 4.

[0114] Advantageously, the modification means 28 of the detection system 2 selects a modification value of the basing voltage in the previously determined table of correspondence between a variation of the basing voltage and a variation of the value representative of at least part of the response signals.

[0115] Preferably, the modification of the basing voltage is carried out between two successive image acquisitions of the detection system 2, that is to say in an image interframe or “dead time” between the acquisition of two successive images.

[0116] Carrying out the modification of the basing voltage in the image interframe makes it possible to avoid the appearance of an intensity level gradient on the image of the observed scene 4, in particular in the case of an implementation of the “rolling shutter” type detection system 2 in Anglo-Saxon terms, the basing voltage being applied sequentially by line or by column depending on the arrangement of the blind detectors 10.

[0117] When the difference between the value representative of the level of at least part of the response signals and the target value is less than the tolerance threshold, a step 46 is carried out for estimating a correction table for the additive non-uniformities of the sensor 6, preferably facing the scene 4.

[0118] For example, during estimation step 46, the detection system 2 implements a calibration method on a scene background that is as uniform as possible, in particular by closing a shutter or by defocusing an optic of the arrangement 14, or a calibration method on the scene based on the optical flow or based on statistical criteria for filtering the textured elements of the scene.

[0119] Step 46 of estimating the correction table of the non-uniformities in additive of the sensor 6 carried out facing the scene 4 improves the quality of restoration of the images of the scene 4.

[0120] The gain non-uniformity correction table associated with the additive non-uniformity correction table of the sensor 6 allows the computer 20 to correct the images from the active detectors 8 produced by the sensor 6, digitized by proximity electronics. This correction in gains and additive of sensor 6 is called “2 points”.

[0121] Preferably, once the correction table for additive non-uniformities of the sensor 6 has been estimated, the steps 42 of acquiring images of the scene 4 and 44 of controlling the basing voltage are carried out again, the detection system 2 then being operational.

[0122] Advantageously, the correction table for additive non-uniformities of the sensor 6 is regularly updated.

[0123] Alternatively, the additive non-uniformity correction table adapted to the modification of the basing voltage is estimated from the current additive non-uniformity correction table of the sensor 6. For example, the additive non-uniformity correction table adapted to the modification of the basing voltage is equal to the current additive non-uniformity correction table of the sensor 6 to which a term equal to the variation in the intensity level of the pixels of the images of the scene 4 following the modification of the basing voltage multiplied by the gain non-uniformity correction table is added. For example, the additive non-uniformity correction table of the sensor 6 is updated using a decolumnizing and / or delineating algorithm, in particular according to the row or column architecture of the blind detectors 10.

[0124] [Fig. 3] schematically represents the steps of preliminary adjustment of the system 2 detection, in particular in the factory, in order to determine and record in the memory of the computer 20 the tables previously determined at least as a function of the temperature of the detection system 2.

[0125] For different predetermined temperature segments of the detection system 2, a step 48 is carried out of recording a value in the table of polarization voltage values ​​of the active detectors 8. For several temperatures of the detection system 2 or of the sensor 6, and for several reference scenes, polarization voltage values ​​of the active detectors 8 are established and recorded, selected to reduce the measurement noise of the detection system 2, in other words to reduce the NETD, while guaranteeing minimal resistance to the total temperature dynamics of the scene 4.

[0126] A step 50 is then carried out of recording a value in the previously determined table of CTIA gain values. For several temperatures of the detection system 2 or of the sensor 6, CTIA gain values ​​selected to reduce the digital conversion noise of the detection system 2 are recorded.

[0127] Preferably, the highest CTIA gain values ​​allowing the total temperature dynamics of scene 4 to be maintained will be selected and recorded simultaneously with the bias voltages of the active detectors 8 so as to reduce jointly the measurement noise and digital conversion values ​​of the detection system 2.

[0128] Advantageously, said tables of values ​​of bias voltages of the active detectors 8, or active pixels, and of the CTIA gains are established for the highest temperature value of each predetermined segment of temperatures of the detection system 2, the highest temperature value being the value of greatest constraint in terms of total temperature dynamics of the scene 4 to be held by the predetermined segment of temperatures of the detection system 2.

[0129] For example, for each high temperature of each temperature segment of the detection system 2, the lowest CTIA gain available by design of the detection system 2 is first selected and the value of the bias voltage of the active detectors 8 is varied. For each bias voltage value of the active detectors 8, at least two scenes of distinct known constant uniform temperatures are imaged, making it possible on the one hand to evaluate the noise of the detection system 2 and on the other hand to convert into the sensor space the desired or estimated values ​​of the total temperature dynamics of the scene 4 to be maintained.The value of the bias voltage of the active detectors 8 minimizing the noise of the detection system 2 is recorded, the value of the bias voltage of the active detectors 8 selected also making it possible to encompass or at least match the total desired or estimated temperature dynamics of scene 4 to the dynamics of the sensor 6. It is then tested whether a larger CTIA gain makes it possible to respect the total desired or estimated temperature dynamics of scene 4 so as to further reduce the digital conversion noise. The highest possible CTIA gain while maintaining the total temperature dynamics of scene 4 is recorded in the CTIA gain table.

[0130] For example, for a temperature of the sensor 6 of +20°C at the top of a segment [0°C, 20°C], it is estimated that there is a need for total dynamic temperature of the scene 4 from 0°C to +40°C, i.e. an absence of saturation for scene elements between 0°C and 40°C. Two acquisitions in front of two distinct reference scenes presented to the detection system 2 make it possible to deduce the range occupied by the excursion going from 0°C to 40°C at the output of the sensor 6, the excursion being, for example, expressed in volts or digital level. If this excursion does not fit into the dynamic range of the sensor 6, corresponding to the difference between the maximum analog-digital conversion voltage value of the detection system 2 and the minimum analog-digital conversion voltage value of the detection system 2, then the tested polarization of the active bolometers is not suitable.If this excursion is compatible with the dynamics of sensor 6, then we calculate the noise on the reference scenes presented to the detection system 2. Once all . the tested active pixel polarization values, the value ensuring the lowest noise is retained, it is recorded in the table of active pixel polarizations and it is associated with the segment [0°C, 20°C]. Finally, for the retained active pixel polarization, we evaluate among the available CTIA gains which allow to hold the total temperature dynamics of scene 4 and we select the largest value which is recorded in the previously determined table of CTIA gain values.

[0131] This logic of searching for the polarizations of the active pixels and the CTIA gain per predetermined temperature segment of the detection system 2 can be repeated in the factory for each detection system 2 to be produced or, more simply, can be considered as stable and pre-established from a few detection systems 2 so as not to be re-estimated for each detection system 2, the procedure being long.

[0132] For each predetermined temperature segment of the detection system 2, a step 52 is also performed for recording the polarization of the blind detectors 10, or basing pixels, in a previously determined table of basing voltage values. For several temperatures of the detection system 2 or of the sensor 6 and for several reference scenes, basing voltage values ​​are selected and recorded to adapt the representative value of at least a portion of the response signals to a target value, the target value being determined to allow the maintenance of a high scene dynamic range and the maintenance of a low scene dynamic range, that is to say to not saturate a scene of estimated high temperature and to not saturate a scene of estimated low temperature.For example, for each temperature of the detection system 2, with a fixed bias voltage of the active detectors 8 and a fixed CTIA gain value, a scene of known constant temperature is imaged, the value of the basing voltage is varied and the value of the basing voltage is recorded such that the representative value of at least part of the response signals corresponds to the target value.

[0133] When initializing the detection system 2, the application of a base voltage value adapted to the temperature of the detection system 2 or of the sensor 6 makes it possible to accelerate the convergence of the deviation towards a value lower than the tolerance threshold.

[0134] Advantageously, it is possible to record not a single base voltage value applicable to the predetermined temperature segment of the detection system 2 but a function applicable to said predetermined temperature segment, for example polynomial, in particular dependent on the temperature of the detection system 2.

[0135] For each temperature segment of the detection system 2, a step 54 is carried out for recording a correspondence value between a variation in the base voltage and the associated variation in the value representative of at least a portion of the response signals. For several temperatures of the detection system 2 or of the sensor 6, for each pair of polarization voltage of the active detectors 8 and CTIA gain, the variation value of the representative value of at least part of the response signals is recorded as a function of the variation of the basing voltage. Exploited by an embedded servo algorithm in the computer 20 of the detection system 2, said correspondence value makes it possible to accelerate the convergence of the deviation towards a value lower than the tolerance threshold.

[0136] Advantageously, it is possible to record not a single correspondence value applicable to the temperature segment of the detection system 2 but a function applicable to the predetermined temperature segment, for example polynomial, in particular dependent on the temperature of the detection system 2.

[0137] Finally, a step 56 is carried out for recording the tables for correcting the gain and additive non-uniformities of the sensor 6. Preferably for several bias voltage values ​​of the active detectors 8, preferably for several basing voltage values ​​for the additive table, preferably for several CTIA gain values ​​and preferably for several temperature values ​​of the detection system 2 or of the sensor 6, a table for correcting the additive non-uniformities of the sensor 6 and a table for correcting the gain non-uniformities of the sensor 6 are established and recorded, in order to compensate for the spatial non-uniformities of the images of the scene 4 formed by the detection system 2 by the computer 20. The tables for correcting the additive and gain non-uniformities of the sensor 6 are, for example, established by carrying out two acquisitions on uniform scenes with two distinct temperatures.

[0138] Alternatively, the order of steps 54 of recording a correspondence value between a variation in the basing voltage and the variation in the value representative of at least part of the response signals and 56 of recording the tables for correcting the non-uniformities in gains and additive of the sensor 6 could be reversed.

[0139] Advantageously, it is possible to search for the optimum polarization of the active pixels at several temperatures of the detection system 2 or of the sensor 6 within a predetermined segment of temperatures of the detection system 2. Then, record not a single value of polarization voltage of the active pixels applicable to the predetermined segment of temperatures of the detection system 2 but a function applicable to the predetermined segment of temperatures, for example polynomial, in particular dependent on the temperature of the detection system 2.

[0140] Advantageously, the tables established for a division into predetermined temperature segments of the detection system 2, for example for temperatures between -40°C and -10°C, between 10°C and +40°C and between +40°C and +70°C, can be established in the form of functions in particular in order to reduce the quantity of data recorded in the memory of the computer 20.

Claims

Claims

1. Method for adjusting a detection system (2) forming a succession of images of a scene (4), the detection system (2) comprising a sensor (6) provided with a matrix of detectors sensitive (8) to electromagnetic radiation coming from the scene (4), called "active", a plurality of detectors insensitive (10) to said radiation, called "blind", as well as a reading circuit (12) providing a response signal for each sensitive detector (8), characterized in that it comprises: - the calculation of a value representative of the level of at least part of the response signals; - the determination of a difference between said representative value and a target value; - the comparison of the difference with a tolerance threshold; and - according to the result of the comparison, the modification of a bias voltage applied to the insensitive detectors (10) called "base voltage", in order to reduce the difference;method in which the value of the modification of the basing voltage is selected, at least as a function of said difference, in a previously determined table of correspondence between a variation of the basing voltage and a variation of the value representative of the level of at least part of the response signals.;

2. The adjustment method according to claim 1, wherein the target value corresponds to a value between a minimum analog-to-digital conversion voltage value of the detection system (2) and a maximum analog-to-digital conversion voltage value of the detection system (2).

3. An adjustment method according to claim 2, wherein the target value corresponds to a value close to the middle of the analog-to-digital conversion range of the detection system (2).

4. Method according to any one of claims 1 to 3, in which the modification of the basing voltage is carried out between two successive image acquisitions of the detection system (2).

5. Method according to any one of claims 1 to 4, comprising an initialization of the detection system (2) during which a bias voltage value of the active detectors (8) and / or a bias voltage value of the blind detectors (10) and / or a trans-impedance capacitive amplification gain value of the sensor (6) is selected at least as a function of a measurement of the temperature of the detection system (2).

6. A method according to claim 5, wherein the bias voltage value of the active detectors (6) and / or the bias voltage value of the blind detectors (10) and / or the trans-impedance capacitive amplification gain value of the sensor (6) is also selected based on an estimated operational measurement need.

7. Method according to one of claims 5 and 6, wherein the bias voltage value of the active detectors (6) and / or the bias voltage value of the blind detectors (10) and / or the trans-impedance capacitive amplification gain value of the sensor (6) is selected from a previously determined table of values, the values ​​contained in said previously determined table of values ​​being established for several temperatures of the detection system (2) and by the use of several reference scenes.

8. Method according to any one of claims 1 to 7, comprising, following the modification of the base voltage, in particular when said deviation is less than the tolerance threshold, the application of a correction table for non-uniformities in additive of the sensor (6) adapted to the modification of the base voltage.

9. Method according to claim 8, in which the correction table for additive non-uniformities of the sensor (6) adapted to the modification of the basing voltage is equal to a current correction table for additive non-uniformities of the sensor (6) to which is added a term equal to the variation in the intensity level of the pixels of the images of the scene (4) following the modification of the basing voltage multiplied by a correction table for gain non-uniformities.

10. Method according to claim 9, in which the correction table of additive non-uniformities of the sensor (6) is updated using a decolumnizing and / or delineating algorithm.

11. Adjustment device (16) for a detection system (2) forming an image of a scene (4), the detection system (2) comprising a sensor (6) provided with a matrix of sensitive detectors (8) to electromagnetic radiation coming from the scene (4), called "active", of a plurality of detectors (10) insensitive to said radiation, called "blind", as well as a reading circuit (12) providing a response signal for each sensitive detector (8), characterized in that it comprises: - a means (22) for calculating a value representative of the level of at least part of the response signals; - a means for determining (24) a difference between said representative value and a target value; - a means of comparing (26) the deviation to a tolerance threshold; - a means (28) for modifying a bias voltage applied to the insensitive detectors (10), called the “base voltage”; and - a calculator (20) provided with a memory, the memory comprising a previously determined correspondence table between a variation in the base voltage and a variation in the value representative of at least part of the response signals.

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