Method for determining calibration information and producing images for an image sensor and associated image sensor

Abstract

The invention relates to a method for determining calibration information for an image sensor comprising a plurality of pixels, the method comprising: obtaining (S1) at least two calibration tables (10 to 13) associated with the image sensor, each calibration table (10 to 13) containing, for each pixel, calibration information, the calibration information from the calibration table (10 to 13) being organised in a series ordered according to a successive order of the pixels (OP), and constructing (S2) at least one correction table (20, 21) for the image sensor, each correction table (20, 21) containing the calibration information from at least two calibration tables (10 to 13), the calibration information in the correction table (20, 21) being organised in a series ordered according to the successive order of the pixels (OP).

Description

[0001] METHODS FOR DETERMINING CALIBRATION INFORMATION AND PRODUCING IMAGES FOR AN IMAGE SENSOR, AND IMAGE SENSOR

[0002] TECHNICAL FIELD

[0003] The present invention relates to image sensors comprising a plurality of pixels, and more particularly to infrared type sensors. The invention also relates to methods for determining calibration information and for generating images for such image sensors.

[0004] STATE OF THE ART

[0005] Currently, image sensors are used in various technical fields. For example, image sensors can be integrated into smart mobile phones. In this case, it is interesting to provide sensors that consume as little electrical energy as possible in order to maintain the longest possible operating time of the phone. In other fields, infrared sensors, i.e., sensors sensitive to infrared radiation, can be used, particularly for viewing scenes in the dark. Such infrared sensors can be integrated into portable binoculars, and it is also interesting to provide sensors with low power consumption in order to limit the weight of the batteries of such binoculars.

[0006] Generally, sensors are equipped with photosensitive receivers configured to convert electromagnetic radiation into an analog electrical signal intended to produce a digital image, i.e. an image comprising a plurality of pixels, from the analog electrical signals. One of the main problems with these receivers is thermal drift of the receivers. This problem particularly concerns infrared sensors. Thus, this drift involves calibrating the sensors to obtain a digital image as close as possible to reality. We can cite the American patent application US2007029484 which discloses a reading circuit for a microbolometric detector array using a temperature sensor so as to compensate the detector measurements for errors induced by temperature in the reading of the microbolometer array.The document discloses the use of a memory that could contain a "pixel map," that is, one that would contain the desired state of a selection switch for each microbolometer in the array. But these readout circuits are complex, and they also use selection switches whose commands consume electrical energy.

[0007] We can also cite the French patent application FR3107116 which discloses a method for calibrating an optoelectronic device of the bolometer type, in which the device is placed in a climatic chamber, the temperature inside the climatic chamber is modified, the polarization voltage of each bolometer is recorded and, for each bolometer, a correction electrical voltage value is recorded as a function of the temperature. The values ​​are recorded in tables. But this method requires the creation of numerous tables of values, the reading of which also consumes electrical energy, particularly when the optoelectronic device is to be used for video acquisition.

[0008] Additionally, US patent application US8378290 discloses a calibration method for an infrared camera, in which correction data determined during a calibration procedure are recorded. The calibration information is recorded in a digital file loaded into the camera's memory. However, accessing the correction data stored in a digital file also consumes electrical energy.

[0009] An object of the invention is to overcome these drawbacks, and more particularly to provide means for producing digital images of improved quality, while consuming as little electrical energy as possible.

[0010] SUMMARY

[0011] To achieve this objective, a method is proposed for determining calibration information for an image sensor comprising a plurality of pixels, the method comprising obtaining at least two calibration tables associated with the image sensor, each calibration table containing, for each pixel, a piece of calibration information, the calibration information of the calibration table being organized in a series ordered according to a successive order of the pixels.

[0012] The method comprises constructing at least one correction table for the image sensor, each correction table containing the calibration information of at least two calibration tables, the calibration information of the correction table being organized in an ordered series according to the successive order of the pixels.

[0013] Thus, correction tables are provided containing calibration information adapted to limit access to the information they contain. Thus, when one wishes to use these correction tables, in particular to correct a temperature drift of an image sensor, one limits the power consumption of the sensor. These correction tables are particularly suitable for use in portable compact devices, in particular devices using batteries, such as binoculars or smart mobile phones.

[0014] There is also provided a method for producing images comprising a plurality of pixels, the method comprising: recording in at least one memory of an image sensor at least one correction table for the image sensor constructed by the method as defined above; successive acquisition, in a successive order of the pixels, of the image frame data generated by the image sensor; access to said at least one memory comprising reading the calibration information contained in said at least one correction table; and successive application, in the successive order of the pixels, of the calibration information contained in said at least one correction table to the image frame data.

[0015] Such a process makes it possible to improve the quality of images provided by an image sensor, while limiting the sensor's power consumption.

[0016] Also provided is an image sensor comprising a plurality of pixels, the sensor comprising at least one memory containing at least one correction table for the image sensor.

[0017] Said at least one correction table is constructed by the method of determining calibration information as defined above.

[0018] According to another aspect of the invention, there is provided a computer program product for determining calibration information, comprising instructions which, when executed by an electronic control unit, enable the electronic control unit to carry out the steps of the method for determining calibration information as defined above.

[0019] Also provided is a computer program product for producing images comprising a plurality of pixels, comprising instructions which, when executed by an electronic control unit, enable the electronic control unit to carry out the steps of the image production method as defined above.

[0020] BRIEF DESCRIPTION OF THE FIGURES

[0021] The aims, objects, as well as the characteristics and advantages of the invention will emerge more clearly from the detailed description of embodiments and implementations thereof, illustrated by the following accompanying drawings in which: Figure 1 schematically illustrates an embodiment of an image sensor; Figure 2 schematically illustrates the main steps of a calibration phase of an image sensor; Figure 3 schematically illustrates the main steps of an implementation of a method for developing images; and Figure 4 schematically illustrates the main steps of an implementation of a method for determining calibration information. The drawings are given as examples and are not limiting of the invention.They constitute schematic representations of principle intended to facilitate understanding of the invention and are not necessarily on the scale of practical applications.

[0022] DETAILED DESCRIPTION

[0023] Before commencing a detailed review of embodiments and implementations of the invention, optional features which may possibly be used in combination or alternatively are set out below.

[0024] According to an example:

[0025] - The construction of each correction table comprises an interleaving of the calibration information of said at least two calibration tables so that the calibration information of the correction table is organized, for each pixel, according to a successive order of the calibration tables.

[0026] - The calibration information of at least one calibration table, called the calibration table at a specific temperature, includes parameters for correcting non-uniformity of the image sensor at the specific temperature.

[0027] - Obtaining comprises obtaining several calibration tables, called calibration tables at distinct specific temperatures, and constructing comprises constructing at least one correction table containing the calibration information of at least two calibration tables at distinct specific temperatures.

[0028] - Obtaining comprises obtaining at least three calibration tables, called calibration tables at three distinct specific temperatures, and constructing comprises constructing at least one correction table containing the calibration information of said at least three calibration tables at distinct specific temperatures.

[0029] - Obtaining comprises obtaining at least three calibration tables, called calibration tables at three distinct specific temperatures, and constructing comprises constructing a first correction table containing the calibration information of a first and a second calibration table at two successive temperatures according to the successive order of the calibration tables, and a second correction table containing the calibration information of the second and a third calibration table at a specific temperature successive to that of the second calibration table according to the successive order of the calibration tables.

[0030] - The calibration information in a calibration table, called a gain table, includes calibration gains.

[0031] - The construction includes a construction of at least two correction tables, each correction table containing the calibration information of the payoff table.

[0032] - Acquisition is performed on the fly, i.e. without recording image frame data.

[0033] - Reading is performed on the fly, i.e. without recording calibration information.

[0034] - Acquisition and reading are carried out, for each pixel, synchronously.- Said at least one correction table is constructed by the method for determining calibration information as defined above, said at least one correction table comprising parameters for correcting non-uniformity of the image sensor at at least two distinct specific temperatures, the method comprising a recording in said at least one memory of a correspondence list between said at least one correction table and at least one temperature interval having as lower and upper limits respectively said at least two distinct specific temperatures, and in which the acquisition comprises a reading of a temperature of the image sensor, and the access comprises a reading of the calibration information contained in the correction table for which the temperature of the image sensor is included in the corresponding temperature interval of the correction table.

[0035] - The image development process includes, after access and before application, for each pixel, a demultiplexing of the calibration information.

[0036] - The sensor comprises a first memory comprising at least one correction table containing non-uniformity correction parameters of the image sensor at at least one specific temperature and a second memory comprising a gain table containing, for each pixel, calibration gains organized in an ordered series according to a successive order of the pixels.

[0037] - Said at least one memory is a non-volatile memory configured as read-only.

[0038] - The sensor comprises an electronic control unit configured to implement the image development method as defined above.

[0039] - The electronic control unit includes a programmable logic circuit of the FPGA type, i.e. a programmable logic gate array.

[0040] In Figures 1 to 3, an image sensor 1 is shown. The sensor 1 is configured to provide a digital image, in other words an image comprising a plurality of pixels. The images each comprise the same number of pixels, and the pixels are ordered in an image in columns and in rows in the form of a pixel matrix. Furthermore, the sensor 1 comprises a plurality of photosensitive receivers Ri (i being an integer used to reference a receiver), typically bolometers, arranged in rows 3 and columns 4, and form a matrix of receivers 5. The sensor 1 comprises a housing 8 within which the matrix of receivers 5 is housed. For the purposes of simplification, and by way of example, a matrix 5 comprising ten receivers R1 to R10 (i being between 1 and 10) is shown. It is also said that the receivers Ri are ordered in the matrix 5, according to a successive order of the receivers OR.Each photosensitive receiver Ri is configured to convert electromagnetic radiation into an analog electrical signal intended to produce a digital image. Thus, the value of a pixel of an image corresponds to the value of the analog electrical signal coming from a photosensitive receiver Ri. Advantageously, the image sensor 1 may comprise a device 14 for measuring the temperature of the image sensor 1.

[0041] It turns out that the photosensitive receivers Ri exhibit a non-uniformity as a function of temperature. In other words, there is a temperature drift of the sensor 1 . That is to say, for a given temperature of the sensor 1 , and when the sensor 1 receives electromagnetic radiation coming from a homogeneous object, in particular a black body 2, the photosensitive receivers Ri do not all generate the same analog electrical signals. A black body 2 is understood to be an element or a device whose temperature is considered stable and whose emissivity s of its surface is close to 1 , more particularly strictly greater than 0.97. The emissivity s of a material is the ratio between the quantity of energy emitted by its surface and the energy emitted by a black body 2 brought to the same temperature. The emissivity is therefore unitless and between 0 and 1 (1 being the value for a perfect black body).

[0042] In order to correct the temperature drift of the photosensitive receivers Ri, calibration information is used.

[0043] In Figure 4, the main steps of a method for determining calibration information for an image sensor 1 comprising a plurality of pixels are shown.

[0044] Generally, the method comprises obtaining S1 at least two calibration tables 10 to 13, and constructing S2 at least one correction table 20, 21 for the image sensor 1.

[0045] The calibration tables 10 to 13 are associated with the image sensor 1, that is to say they contain calibration information previously obtained during a calibration phase of the image sensor 1. An example of a calibration phase will be described later. In particular, each calibration table 10 to 13 contains, for each pixel, a piece of calibration information. In FIG. 1, for example, an image sensor 1 comprising ten photosensitive receptors Ri has been shown. In this case, each calibration table 10 to 13 contains at least ten pieces of calibration information, that is to say at least one piece of calibration information per pixel. For example, a piece of calibration information may comprise a correction parameter PCi(Tj) for non-uniformity of the image sensor 1 at a specific temperature Tj (i being the integer used to reference a receptor and j an integer to reference a temperature).In the example illustrated in Figure 4, three specific temperatures T1 to T3 are represented, j being between 1 and 3. Such a correction parameter PCi(Tj) makes it possible to correct the electrical signal generated by a receiver Ri, when the sensor 1 is at a specific temperature T1 to T3. In other words, the correction parameters PCi(Tj) are a function of a specific temperature T1 to T3. A calibration table 10 to 12 containing correction parameters PCi(Tj) is also noted as a calibration table at a specific temperature T1 to T3. In other words, a calibration table at the specific temperature T1 contains correction parameters PCi(T1) of non-uniformity of the image sensor 1 at the specific temperature T1. According to another example, calibration information may comprise a calibration gain GPi (i being the integer used to reference a receiver).A calibration gain GPi, unlike the correction parameters PCi(Tj), is not a function of temperature. That is to say, a calibration gain GPi makes it possible to correct an electrical signal generated by a receiver Ri regardless of the temperature of the sensor 1. Furthermore, the calibration table 13 containing calibration gains is also denoted gain table. In FIG. 4, the gain table 13 comprises ten calibration gains GP1 to GP10. In particular, for each calibration table 10 to 13, the calibration information is organized in a series ordered according to a successive order of the pixels OP. In particular, all the calibration tables 10 to 13 contain calibration information ordered in the same way. Preferably, the successive order of the pixels OP in an image is identical to the successive order of the receivers OR of the sensor 1.In other words, the first calibration information of each of the calibration tables 10 to 13 makes it possible to correct the analog electrical signal generated by the first receiver R1 of the receiver matrix 5. Furthermore, the second calibration information of each of the calibration tables 10 to 13 makes it possible to correct the analog electrical signal generated by the second receiver R2 of the receiver matrix 5, and so on. The calibration information is associated with the receiver Ri of the sensor 1, and it is said that the calibration tables 10 to 13 are associated with the sensor 1.

[0046] The calibration tables 10 to 13 can be obtained during a calibration phase. Figure 2 shows the main possible steps of the calibration phase. The calibration phase comprises placing the image sensor 1 in a climatic chamber 50. The climatic chamber 50 comprises a black body 2 placed opposite the image sensor 1. Furthermore, the calibration phase comprises modifying the temperature inside the climatic chamber 50 to reach a first temperature T1, then waiting for a stabilization time so that the temperature of the image sensor 1 is constant, preferably equal to T1. Then, the image sensor 1 generates an analog electrical signal, from each of the photosensitive receivers Ri, in order to provide values ​​as a function of the temperature T1.For example, these values ​​may correspond to the non-uniformity correction parameters of the image sensor at the specific temperature T1. Generally, a correction parameter PCi(Tj) is determined as a function of the value of the analog electrical signal generated by the receiver Ri at a specific temperature Tj. Then, the correction parameters PCi(T1) at the specific temperature T1 are recorded in the calibration table 10 at the temperature T1. In addition, the calibration phase comprises a modification of the temperature inside the climatic chamber 50 to reach a second temperature T2 different from T1, preferably greater than T1, then a repetition of the waiting and recording steps in order to obtain non-uniformity correction parameters PCi(Tj) of the image sensor at other specific temperatures T2, T3.Thus, the non-uniformity correction parameters PCi(T2) at a second specific temperature T2 are recorded in the calibration table 11 at the temperature T2 and the non-uniformity correction parameters PCi(T3) at the third specific temperature T3 are recorded in the calibration table 12 at the temperature T3.

[0047] Advantageously, the calibration phase comprises a comparison of the values ​​of the analog electrical signals generated at a specific temperature T1 to T3, in order to determine the calibration gain GPi, for each photosensitive receiver Ri. Then, the determined gains are recorded in the gains table 13. It is noted that the value of the gains is not a function of the temperature. The construction S2 of at least one correction table 20, 21 is intended to improve access to the calibration information, in terms of speed and quantity of electrical energy consumed.

[0048] More particularly, the construction S2 of at least one correction table 20,21 is carried out in the following manner: each correction table 20,21 contains the calibration information of at least two calibration tables 10 to 13. Thus, a correction table 20,21 can contain correction parameters PCi(Tj) from two calibration tables 10 to 12 associated respectively with two distinct specific temperatures T1 to T3. According to another example, a correction table 20,21 can contain calibration gains GPi and correction parameters PCi(Tj). In particular, each correction table 20,21 corresponds to a list of calibration information ordered according to a column. This facilitates access to the information it contains. It is also said that the correction tables 20,21 have a single read entry.Generally, the calibration information of each correction table 20, 21 is organized in a series ordered according to the successive order of the pixels OP. That is to say that the first calibration information of each correction table 20, 21 is associated with the first pixel of an image, or with the first receptor R1 of the sensor 1. The second calibration information of each of the correction tables 20, 21, which follows the first information, is associated with the second pixel of the image, or with the second receptor R2 of the sensor 1, and so on.

[0049] Such an ordering of the calibration information in the correction tables 20, 21 makes it easier to access the information in these correction tables 20, 21, and thus limits the amount of electrical energy consumed to read the information. Indeed, if one wishes to access the calibration information from the calibration tables 10 to 13, at least two accesses will be required if one wishes to access the information from two calibration tables 10 to 13. On the contrary, by using a correction table 20, 21, there is only one access necessary to read the information from two calibration tables 10 to 13.

[0050] Preferably, the construction S2 of at least one correction table 20, 21 comprises an interleaving of the calibration information of at least two calibration tables 10 to 13 so that the calibration information of the correction table 20, 21 is organized, for each pixel, according to a successive order of the calibration tables OC1, OC2. It is also said that the calibration information is interleaved, or even multiplexed, and it is also said that the correction tables 20, 21 are multiplexed. The successive orders of the calibration tables OC1, OC2 are determined beforehand. In particular, a successive order of the calibration tables OC1, OC2 is repeated, for each pixel, periodically for the same correction table 20, 21. According to the example illustrated in FIG. 4, two correction tables 20, 21 are constructed S2.Prior to construction S2, three calibration tables 10 to 12 are obtained at three specific temperatures T1 to T3 and a fourth gain table 13. In this example, a first successive order of the first calibration table OC1 may be the first table 10, the second table 11, and the fourth gain table 13. A second successive order of the second calibration table OC2 may be the second table 11, the third table 12 and the fourth gain table 13. It may be noted that, for each pixel, the calibration information of each correction table 20, 21 is ordered according to the same successive order of the calibration tables OC1, OC2. Preferably, the successive orders of the calibration tables OC1, OC2 follow the successive order of the temperatures T1 to T3.

[0051] There are several variations for constructing the correction tables 20,21.

[0052] For example, a correction table 20,21 can be constructed from at least two calibration tables at two distinct specific temperatures T1 to T3. In this case, the construction S2 comprises a construction of at least one correction table 20,21 containing the calibration information of at least two calibration tables at distinct specific temperatures T1 to T3.

[0053] It is also possible to construct the same correction table 20, 21 from at least three calibration tables 10 to 12 at specific temperatures T1 to T3. In this case, the construction S2 comprises a construction of at least one correction table 20, 21 containing the calibration information of said at least three calibration tables 10 to 12 at distinct specific temperatures T1 to T3.

[0054] Advantageously, several correction tables 20, 21 can be constructed from at least three calibration tables 10 to 12 at three distinct specific temperatures T1 to T3, so that each correction table 20, 21 is constructed from two calibration tables 10 to 12, by changing calibration tables 10 to 12 for each correction table 20, 21.In this case, the construction S2 comprises a construction of a first correction table 20 containing the calibration information of a first and a second calibration table 10, 11 at two successive temperatures T1, T2 according to a first successive order of the calibration tables OC1, and of a second correction table 21 containing the calibration information of the second calibration table 11 and of a third calibration table 12 at the third specific temperature T3 successive to that of the second calibration table 12 according to a second successive order of the calibration tables OC2.

[0055] According to another advantage, several correction tables 20, 21 can be constructed from the same gain table 13. In this case, the construction S2 comprises a construction of at least two correction tables 20, 21, each correction table 20, 21 containing the calibration information of the gain table 13. In this case, the gains are found in the two correction tables 20, 21, and are deliberately redundant values. Thus, the size of the correction tables 20, 21 is deliberately increased, but the number of accesses to the correction tables remains limited to the number of correction tables 20, 21, which limits the quantity of electrical energy to access the information.

[0056] In Figure 4, an example of construction of correction tables 20, 21 is shown from three calibration tables 10 to 12 at three distinct temperatures T1 to T3 and from a gain table 13. For example, the temperatures are consecutive, and T1 is equal to 5°C, T2 is equal to 10°C and T3 is equal to 15°C.

[0057] The method for determining calibration information may further comprise a recording S3 of the correction tables 20, 21 in a memory 6. Preferably, the memory 6 is a non-volatile memory configured as read-only. A non-volatile memory can retain its recorded data even when it is no longer electrically powered. For example, the memory 6 is a flash-type memory. Flash memories are non-volatile memories configured as read-only which are also fast to read and erasable by complete sectors. Furthermore, a flash memory allows modification of several memory spaces in a single operation. A flash memory allows faster read access to data than write access.

[0058] In Figure 3, the main steps of an embodiment of an image generation method are shown. Also shown is the image sensor 1 comprising the matrix of photosensitive receptors 5, an electronic control unit 30 and the memory 6. The electronic control unit 30 is configured to implement the image generation method. The electronic control unit 30 may comprise a programmable logic circuit of the FPGA type, i.e. a programmable logic gate array. Generally, the image sensor 1 comprises an analog / digital converter 35 coupled to the photosensitive receptors Ri, by a first connection 39, and configured to digitize the analog electrical signals generated by the photosensitive receptors Ri. In other words, the converter 35 transforms the analog electrical signals into digital signals.The converter 35 can be integrated within the electronic control unit 30, or alternatively it can be integrated within the matrix of photosensitive receivers 5. More particularly, the converter 35 is configured to transmit, via a second connection 40, the values ​​of the digital electrical signals in the form of an image frame. Generally, the data of an image frame contains the values ​​of the digital electrical signals, typically values ​​corresponding to the voltages from the photosensitive receivers Ri. The data of an image frame is intended to form the image. Each pixel of an image is developed from the value of a data item of an image frame. In particular, the values ​​of the data of an image frame are a function of a temperature of the image sensor 1. Furthermore, the data of the image frame are ordered in an order corresponding to the successive order of the pixels OP.Thus, the first data of the image frame corresponds to the value of the electrical signal provided by the first photosensitive receptor R1 of the matrix of receptors 5.

[0059] More particularly, the electronic control unit 30 comprises a first circuit 31 for receiving the image frames, coupled to the converter 35 by the second connection 40, and a second processing circuit 32, coupled to the memory 6 by a third connection 41 and configured to perform operations for processing the data from the memory 6. Advantageously, the electronic control unit 30 may comprise a third calculation circuit 33, coupled to the second circuit 32 by a fourth connection 42, and configured to perform calculation operations on the data received from the second circuit 32. Furthermore, the electronic control unit 30 may also comprise a fourth correction circuit 34, coupled to the second and third circuits 32, 33 respectively by fifth and sixth connections 43, 44.The fourth circuit 34 makes it possible to correct the value of the image frame data by applying to these values ​​the calibration information from the correction tables 20, 21 recorded in the memory 6. Furthermore, the fourth correction circuit 34 is coupled to the first reception circuit 31, by a seventh connection 48, to receive the image frames transmitted by the first acquisition circuit 31. Furthermore, the fourth circuit 34 is configured to provide a corrected image, by an eighth connection 46 corresponding to an output of the electronic control unit 30.

[0060] Generally, the image generation method comprises the recording S3 of the correction tables 20, 21 in the memory 6, an acquisition S4 of the image frame data, an access S5 to the memory 6 and an application S6 of the calibration information.

[0061] The correction tables 20, 21, recorded in the memory 6, correspond to the correction tables 20, 21 constructed by the determination method as defined above. For example, the correction tables 20, 21 contain non-uniformity correction parameters of the image sensor 1 and are recorded in a first memory 6 and the gain tables 13 can be recorded either in the first memory 6 or in a separate second memory 7. Preferably, the second memory 7 is of the same type as the first memory 6. The second memory 7 is coupled to the second processing circuit 32, by a ninth connection 47. The acquisition S4 comprises a successive acquisition, according to the successive order of the pixels, of the image frame data generated by the converter 35. In particular, the first circuit 31 receives the image frame data and transmits them to the fourth circuit 34, by the seventh connection 48.Furthermore, the access S5 to the memory 6 comprises a reading of the calibration information contained in the correction table(s) 20, 21. The application S6 comprises a successive application, according to the successive order of the pixels OP, of the calibration information contained in the correction table(s) 20, 21 to the image frame data.

[0062] Preferably, the acquisition S4, and the application S6 are carried out for each pixel and in the successive order of the pixels OP. That is to say, for each pixel, the electronic control unit 30, and more particularly the fourth circuit 34, acquires a data item from the image frame, and more particularly the data item associated with the pixel, and applies, to the acquired data item, the calibration information contained in the correction table 20, 21 associated with the pixel.

[0063] Advantageously, the acquisition S4 is performed on the fly, i.e. without recording the image frame data. According to another advantage, the reading of the calibration information, i.e. the reading of a correction table 20,21, is performed on the fly, i.e. without recording the calibration information. More particularly, the reading of a correction table 20,21 is performed from an access to the correction table 20,21 from a specific address AD1, AD2 of the correction table 20,21. Thus, the reading of the calibration information is performed from a single access to a specific address of a correction table 20,21.

[0064] Preferably, the acquisition S4 and the reading are carried out, for each pixel, synchronously. In this case, the circuits 31 to 34 are synchronized with the matrix of the receivers 5, and more particularly with the converter 35. For example, the electronic control unit 30 is coupled to the matrix of the receivers 5, by a tenth connection 45, to receive a clock signal making it possible to synchronize the circuits 31 to 34. Furthermore, the converter 35 can receive the clock signal, by the first connection 39, to be synchronized with the circuits 31 to 34. This improves the speed of the calculation operations, for each pixel, and thus the speed of the image development process.

[0065] Preferably, each correction table 20, 21 comprises non-uniformity correction parameters of the image sensor at at least two distinct specific temperatures T1 to T3. For example, a first correction table 20 containing the correction parameters PCi(T1) and PCi(T2) and a second correction table 21 containing the parameters PCi(T2) and PCi(T3). For example, T1 is equal to 5°C, T2 is equal to 10°C and T3 is equal to 15°C. In addition, the acquisition S4 comprises a reading of a temperature TC of the image sensor 1, for example via the first reception circuit 31, in order to know the temperature TC of the sensor 1 at which the electrical signals were generated by the photosensitive receivers Ri. Advantageously, the first reception circuit 31 can transmit the temperature TC of the sensor 1, to the second processing circuit 32, by an eleventh connection 49, and to the third calculation circuit 33, by a twelfth connection 51.Knowledge of such a temperature TC is used by the electronic control unit 30 to choose the correction table 20,21 making it possible to modify the value of the electrical signals in order to provide a corrected image.

[0066] For example, the temperature TC of the sensor 1 can be transmitted to the electronic control unit 30, and in particular to the first receiving circuit 31, by the image frames. In other words, a specific data item of an image frame comprises the temperature TC of the sensor 1.

[0067] Preferably, the temperature TC read by the first reception circuit 31 of the electronic control unit 30 is used to correct the data of the image frame which follows the previous frame containing the information of the temperature TC of the sensor 1.

[0068] For example, the value of the image frame data can be corrected, as a function of the temperature TC, from the correction parameters PCi(Tj). The fourth circuit 34 is configured to perform, for each pixel, the following calculation:

[0069] Vpixel = Vdata + Vcor ​​(equation 1) where:

[0070] - Vpixel corresponds to the value of a pixel in the image (unitless);

[0071] - Vdata corresponds to the value of the image frame data corresponding to the image pixel (unitless); and

[0072] - Vcor ​​corresponds to a correction value (without unit) associated with the pixel of the image.

[0073] The correction value Vcor ​​may correspond to the value of a correction parameter PCi(Tj). Preferably, the third circuit 33 is configured to perform an interpolation from a correction table 20, 21, for example by calculating the correction value Vcor ​​= (PCi(T1) + PCi(T2)) / 2. According to another example, the third circuit 33 may be configured to perform an interpolation by calculating the correction value Vcor ​​= [(T2-TC) / (T2-T1)]xPCi(T1) + [(TC- T1) / (T2-T1)]xPCi(T2); with T2>T1, and TC between T1 and T2.

[0074] Advantageously, the fourth circuit 34 is configured to gain correct the value of the image frame data, from the GPi calibration gains. The fourth circuit 34 can be configured to calculate, for each pixel, the following calculation: Vpixel = GPi x (Vdata) (equation 2).

[0075] Alternatively, the fourth circuit 34 may be configured to calculate, for each pixel, the following calculation:

[0076] Vpixel = GPi x (Vdata + Vcor) (equation 3).

[0077] Advantageously, the image production method comprises, after access S4 and before application S6, for each pixel, a demultiplexing of the calibration information.

[0078] The second circuit 32 is configured to read the calibration information contained in the correction tables 20, 21. In particular, the second circuit 32 transmits the correction parameters PCi(Tj) to the third circuit 33, when it is desired to perform an interpolation of the data. Alternatively, the second circuit 32 transmits the correction parameters PCi(Tj) to the fourth circuit 34 to calculate the value of the pixel Vpixel without interpolation. When the correction tables 20, 21 contain calibration gains GPi, the second circuit 32 transmits the calibration gains GPi to the fourth circuit 34 to calculate the value of the pixel Vpixel according to equation 2 or 3.

[0079] Advantageously, when an interpolation is to be performed, the third circuit 33 transmits, for each pixel, the correction value Vcor ​​to the fourth circuit 34. The fourth circuit 34 calculates the value of the pixel according to equation 1 or 3.

[0080] The development method may further comprise, after access S4 and before application S6, for each pixel, a demultiplexing of the calibration information. In other words, the second circuit 32 reads the calibration information and performs a demultiplexing of the information to transmit to the third circuit 33 the correction parameters PCi(Tj) at at least two distinct temperatures to perform an interpolation. When a correction table 20, 21 comprises calibration gains GPi, the demultiplexing comprises a transmission of the calibration gains GPi to the fourth circuit 34 to calculate the value of the pixels according to equation 2 or 3.

[0081] Advantageously, the sensor 1 may comprise a correspondence list for correlating the correction tables 20, 21 with at least one temperature value, and preferably a temperature interval having two lower and upper limits. For example, a temperature value may correspond to a correction table 20, 21. According to another example, a temperature interval may correspond to a correction table 20, 21. Advantageously, the correspondence list may further comprise, for each correction table 20, 21, a reference to the address of the correction table 20, 21 in the memory 6. The reference makes it possible to facilitate access S5 to the calibration information. Thus, the preparation method may comprise a recording in the memory 6, or in another separate memory 7, of the correspondence list between the correction tables 20, 21 and the respective temperature values.The acquisition S4 may comprise a reading of a temperature TC of the sensor 1 and the access S5 comprises a reading of the calibration information contained in the correction table 20, 21 whose temperature value is equal to the temperature TC of the sensor 1, i.e. the temperature read previously. According to one embodiment, several correction tables 20, 21 are recorded in the memory 6, and each correction table 20, 21 comprises correction parameters PCi(Tj) at two distinct temperatures, called minimum and maximum temperatures associated with the correction table 20, 21. In this case, the correspondence list comprises, for each correction table 20, 21, a correspondence to a temperature interval having as lower and upper limits respectively the minimum and maximum temperatures associated with the correction table 20, 21.In this case, access S5 includes a reading of the calibration information contained in the correction table 20, 21 for which the temperature TC of the sensor 1 is included in the corresponding temperature interval of the correction table 20, 21.

[0082] The electronic control unit 30 may comprise a computer program comprising instructions for carrying out the steps of the method for determining calibration information as defined above. The computer program may further comprise instructions for carrying out the steps of the method for developing images as defined above.

Claims

Demands 1. A method for determining calibration information for an image sensor comprising a plurality of pixels, the method comprising: - obtaining (S1) at least two calibration tables (10 to 13) associated with the image sensor, each calibration table (10 to 13) containing, for each pixel, calibration information, the calibration information of the calibration table (10 to 13) being organized in an ordered series according to a successive order of pixels (OP), characterized in that the method comprises: - a construction (S2) of at least one correction table (20, 21) for the image sensor, each correction table (20, 21) containing the calibration information of at least two calibration tables (10 to 13), the calibration information of the correction table (20, 21) being organized in an ordered series according to the successive order of pixels (OP).

2. Method according to claim 1, wherein the construction (S2) of each correction table (20, 21) comprises an interleaving of the calibration information of said at least two calibration tables (10 to 13) such that the calibration information of the correction table (20, 21) is organized, for each pixel, according to a successive order of the calibration tables (OC1, OC2).

3. A method according to any one of claims 1 or 2, wherein the calibration information of at least one calibration table (10 to 12), referred to as a calibration table at a specific temperature, includes parameters for correcting non-uniformity of the image sensor at the specific temperature.

4. Method according to claim 3, wherein the obtaining (S1) comprises obtaining several calibration tables (10 to 12), referred to as calibration tables at distinct specific temperatures, and the construction (S2) comprises constructing at least one correction table (20, 21) containing the calibration information of at least two calibration tables at distinct specific temperatures (10 to 12).

5. A method according to any one of claims 3 or 4, wherein the obtaining (S1) comprises obtaining at least three calibration tables (10 to 12), referred to as calibration tables at three distinct specific temperatures, and the construction (S2) comprises constructing at least one correction table (20, 21) containing the calibration information of said at least three calibration tables at distinct specific temperatures (10 to 12).

6. A method according to claim 4, wherein the obtaining (S1) comprises obtaining at least three calibration tables (10 to 12), referred to as calibration tables at three distinct specific temperatures, and the construction comprises constructing a first correction table (20) containing the calibration information of a first and a second calibration tables at two successive temperatures (10, 11) according to a first successive order of calibration tables (OC1), and a second correction table (21) containing the calibration information of the second calibration table and a third calibration table (11, 12) at a specific temperature successive to that of the second calibration table (11) according to a second successive order of calibration tables (OC2).

7. A method according to any one of claims 1 to 6, wherein the calibration information of a calibration table (13), referred to as the gain table, includes calibration gains.

8. Method according to claim 7, wherein the construction (S2) comprises a construction of at least two correction tables (20, 21), each correction table (20, 21) containing the calibration information of the gain table.

9. A method for producing images comprising a plurality of pixels, the method comprising: - a recording (S3) in at least one memory (6, 7) of an image sensor of at least one correction table (20, 21) for the image sensor constructed by the method according to any one of the preceding claims; - a successive acquisition (S4), according to a successive order of pixels (OP), of the image frame data generated by the image sensor; - access (S5) to said at least one memory (6, 7) comprising a read of the calibration information contained in said at least one correction table (20, 21); and - a successive application (S6), according to the successive order of pixels (OP), of the calibration information contained in said at least one correction table (20, 21) to the image frame data.

10. Method according to the preceding claim, wherein the acquisition (S4) is carried out on the fly, i.e. without recording of image frame data.

11. A method according to any one of claims 9 or 10, wherein the reading is carried out on the fly, i.e. without recording calibration information.

12. A method according to any one of claims 9 to 11, wherein the acquisition (S4) and reading are carried out, for each pixel, synchronously.

13. A method according to any one of claims 9 to 11, wherein said at least one correction table (20, 21) is constructed by the calibration information determination method according to any one of claims 4 to 6 alone or in combination with any one of claims 7 to 8, said at least one correction table (20, 21) comprising image sensor non-uniformity correction parameters at at least two distinct specific temperatures, the method comprising storing in said at least one memory (6, 7) a lookup list between said at least one correction table (20, 21) and at least one temperature range having as lower and upper bounds respectively said at least two distinct specific temperatures, and wherein the acquisition (54) includes a reading of a temperature (TC) of the image sensor, and the access (S5) includes a reading of the calibration information contained in the correction table (20, 21) for which the temperature (TC) of the image sensor is within the corresponding temperature range of the correction table (20, 21).

14. A method according to any one of claims 9 to 13, comprising, after access (55) and before application (S6), for each pixel, a demultiplexing of the calibration information.

15. Image sensor comprising a plurality of pixels, the sensor comprising at least one memory (6, 7) containing at least one correction table (20, 21) for the image sensor, characterized in that said at least one correction table (20, 21) is constructed by the calibration information determination method according to any one of claims 1 to 8.

16. Sensor according to the preceding claim, comprising a first memory (6) comprising at least one correction table (20, 21) containing image sensor non-uniformity correction parameters at at least one specific temperature and a second memory (7) comprising a gain table (13) containing, for each pixel, calibration gains organized in a series ordered according to a successive pixel order (OP).

17. Sensor according to any one of the two preceding claims, wherein said at least one memory (6, 7) is a non-volatile memory configured as read-only.

18. Sensor according to any one of claims 15 to 17, comprising an electronic control unit (30) configured to implement the image processing method according to any one of claims 9 to 14.

19. Sensor according to claim 18, wherein the electronic control unit (30) comprises a programmable logic circuit of the FPGA type, i.e. a network of programmable logic gates.

20. Product computer program intended for determining calibration information, comprising instructions which, when executed by an electronic control unit, enable the electronic control unit to perform the steps of the method for determining calibration information according to any one of claims 1 to 8.

21. Product computer program intended for image processing comprising a plurality of pixels, comprising instructions which, when executed by an electronic control unit, enable the electronic control unit to carry out the steps of the image processing method according to any one of claims 9 to 14.

Images