Method for processing an image

Abstract

A method for processing a raw image characterized by raw measurements S.sub.p(i,j) that are associated with active bolometers B.sub.pix_(i,j) of an imager, which bolometers are arranged in a matrix array, the imager being at an ambient temperature T.sub.amb and furthermore comprising blind bolometers B.sub.b_(k), the method, which is executed by a computer that is provided with a memory, comprising the following steps: a) a step of calculating the electrical resistances R.sub.Tc(i,j) and R.sub.Tc(k), at the temperature T.sub.amb, of the active and blind bolometers, respectively, from their respective electrical resistances R.sub.Tr(i,j) and R.sub.Tr(k) at a reference temperature T.sub.r, said resistances being stored in the memory; b) a step of determining the temperatures T.sub.sc(i,j) actually measured by each of the active bolometers B.sub.pix_(i,j) from the electrical resistances calculated in step a) and from the raw measurements S.sub.p(i,j).

Claims

1. Method for processing a raw image characterized by raw measurements S.sub.p(i,j) that are associated with active bolometers B.sub.pix_(i,j) of an imager, which bolometers are arranged in a matrix array of n rows (L.sub.i) and m columns (C.sub.j), the imager being at an ambient temperature T.sub.amb and furthermore comprising blind bolometers B.sub.b_(k), each blind bolometer B.sub.b_(k) being employed for the differential measurement of the active bolometers B.sub.pix_(i,j) of at least one column of bolometers that is specific thereto, each blind bolometer B.sub.b_(k) advantageously being associated with one single column (C.sub.j) of active bolometers B.sub.pix_(i,j), the method, which is executed by a computer that is provided with a memory, comprising the following steps: a) a step of calculating the electrical resistances R.sub.Tc(i,j) and R.sub.Tc(k), at the temperature T.sub.amb, of the active and blind bolometers, respectively, from their respective electrical resistances R.sub.Tr(i,j) and R.sub.Tr(k) at a reference temperature T.sub.r, said resistances being stored in the memory; and b) a step of determining the temperatures T.sub.sc(i,j) actually measured by each of the active bolometers B.sub.pix_(i,j) from the electrical resistances calculated in step a) and from the raw measurements S.sub.p(i,j), wherein the temperature T.sub.sc(i j) actually measured by an active bolometer B.sub.pix_(i,j) respects the following relationship:
S.sub.P(i,j)=Resp(T.sub.amb,i,j)(T.sub.sc(i,j)−T.sub.amb)+S.sub.0,Tamb(i,j) where: Resp(T.sub.c,i,j) is the responsivity of the bolometer, wherein term (T.sub.c,i,j) represents term (T.sub.amb,i,j)(T.sub.sc(i,j)−T.sub.amb); S.sub.0,Tamb(i,j) is the value output by the active bolometer B.sub.pix_(i,j) without any output provided by the blind bolometers, for a temperature actually measured equal to the ambient temperature.

2. Method according to claim 1, wherein step a) of calculating the electrical resistances R.sub.Tc(i,j) and R.sub.Tc(k), at the temperature T.sub.amb, is executed based on an activation energy E.sub.a representative of the material forming each of the active and blind bolometers B.sub.pix_(i,j) and B.sub.b_(k).

3. Method according to claim 2, wherein the electrical resistances R.sub.Tamb(i,j) and R.sub.Tamb(k) are calculated using the following relationships: $R_{\mathrm{Tamb}}\left(i,j\right)=R_{\mathrm{Tr}}\left(i,j\right).Math.e^{\frac{{\mathrm{qE}}_a}{k}\left(\frac{1}{T_{\mathrm{amb}}}-\frac{1}{T_r}\right)}$ $\mathrm{and}$ $R_{\mathrm{Tamb}}\left(k\right)=R_{\mathrm{Tr}}\left(k\right).Math.e^{\frac{{\mathrm{qE}}_a}{k}\left(\frac{1}{T_{\mathrm{amb}}}-\frac{1}{T_r}\right)}$

4. Method according to claim 1, wherein the value S.sub.0,Tamb(i,j) associated with an active bolometer B.sub.pix_(i,j) of a column (C.sub.j) is dependent on the difference between the currents I.sub.0,pix(i,j) and I.sub.0,b(j) capable of flowing through said active bolometer B.sub.pix_(i,j) and the blind bolometer B.sub.b_(k) with which the column (Cj) is associated, respectively, for a temperature actually measured equal to the ambient temperature.

5. Method according to claim 1, step a) being preceded by a step a1) of acquiring raw measurements S.sub.p(i,j) with capacitive transimpedance amplifiers (CTIA) that are arranged so that all of the active bolometers B.sub.pix_(i,j) of each column (C.sub.j) and the blind bolometer B.sub.b_(k) with which said column (Cj) is associated are connected to a negative input (E.sup.−) of one of the capacitive transimpedance amplifiers (CTIA), the positive input (E.sup.+) of said amplifier (CTIA) receiving a reference voltage (V.sub.bus).

6. Method according to claim 5, wherein switching devices, in particular transistors, controlled by the computer are interposed between each of the, active and blind, bolometers and the capacitive transimpedance amplifier (CTIA) to which the latter are connected.

7. Method according to claim 6, wherein prior to the implementation of the method, a step of measuring the electrical resistances R.sub.Tr(i,j) and R.sub.Tr(k) is executed.

8. Method according to claim 7, wherein the determination of the electrical resistance R.sub.Tr(i,j) and R.sub.Tr(k) of an active bolometer B.sub.pix_(i,j) of a column (Cj) or of the blind bolometer B.sub.b_(k) with which said column (Cj) is associated comprises a measurement of the current capable of flowing through the bolometer in question.

9. Method according to claim 8, wherein the measurement of the current capable of flowing through the bolometer in question comprises closing the switch interposed between said bolometer in question and the capacitive transimpedance amplifier (CTIA), the other switches being kept open.

10. A computer program product comprising a non-transitory computer readable medium having a computer program stored thereon, which when executed by a computer, causes the method according to claim 1 to be performed.

11. Imager comprising, active bolometers B.sub.pix_(i,j), of an imager, said bolometers being arranged in a matrix array of n rows (L.sub.i) and m columns (C.sub.j); blind bolometers B.sub.b_(k), each blind bolometer B.sub.b_(k) being employed for the differential measurement of the active bolometers B.sub.pix_(i,j) of at least one column of bolometers that is specific thereto, each blind bolometer B.sub.b_(k) advantageously being associated with a single column (C.sub.j) of active bolometers B.sub.pix_(i,j); and a computer comprising a non-transitory computer readable medium having a computer program stored thereon, which when executed by the computer causes the method according to claim 1 to be performed.

12. Imager according to claim 11, wherein the imager is used for detection of people in a room.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages will become apparent from the following description of a method for processing an image, given by way of nonlimiting examples, with reference to the appended drawings, in which:

(2) FIG. 1 is a raw image of a scene obtained with an imager provided with bolometers arranged in a matrix array of 80 rows by 80 columns;

(3) FIG. 2 is a schematic representation of an imager provided with a lens mounted on a diaphragm capable of being implemented according to the present invention;

(4) FIG. 3 is a representation of an equivalent circuit diagram of the imager, FIG. 3 in particular showing a first column C.sub.1, and an X.sup.th column C.sub.X of active bolometers B.sub.pix_(i,j);

(5) FIG. 4a shows an equivalent circuit diagram resulting from the closure of a single switching device of a given active bolometer;

(6) FIG. 4b shows an equivalent circuit diagram resulting from the closure of a single control transistor of a given blind bolometer, and no current flowing through the other active and blind bolometers.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

(7) The present description will now be described with reference to FIGS. 1 to 4b.

(8) FIG. 2 shows an imager provided with a plurality of active bolometers, denoted B.sub.pix_(i,j), arranged in a matrix array of n rows (denoted “L.sub.i”) and m columns (denoted “C.sub.j”).

(9) A bolometer indexed i, j corresponds to a bolometer placed at the intersection of row i with column j.

(10) The imager of FIG. 2 may also comprise a plurality of blind bolometers B.sub.b_(k).

(11) Each blind bolometer P.sub.b_(k) is employed for the differential measurement of the active bolometers B.sub.pix_(i,j) of at least one column of bolometers that is specific thereto.

(12) In particular, each blind bolometer B.sub.b_(k) is associated with a single column (C.sub.j) of active bolometers B.sub.pix_(i,j).

(13) The imager 1 furthermore comprises a computer 4 equipped with a computational processor intended to execute the various steps of the method according to the present invention.

(14) The computer may also comprise a memory space for saving the raw measurements, and/or parameters useful to the operation of the imager 1.

(15) Lastly, the imager 1 may comprise a temperature probe 5 intended to evaluate the temperature of the environment in which said detector is found. The temperature probe may, for example, comprise a PN junction.

(16) FIG. 3 is a representation of an equivalent circuit diagram of the imager 1. FIG. 3 in particular shows a first column C.sub.1, and an X.sup.th column C.sub.X of active bolometers B.sub.pix_(i,j).

(17) Each of the active bolometers B.sub.pix_(i,j) of a column and the blind bolometer B.sub.b_(j) with which said column is associated, is connected to a common line BL(j) via a switching device I, and in particular a transistor, controlled by the computer.

(18) The end of each of the common lines BL(k) is connected to a negative input E.sup.− of a capacitive transimpedance amplifier CTIA. The positive input E.sup.+ is for its part raised to a reference voltage V.sub.bus.

(19) The use of the switching devices I allows each of the active or blind bolometers to be addressed individually and thus their output signal to be measured with one of the capacitive transimpedance amplifiers CTIA.

(20) The method according to the present invention proposes to correct the defects of a raw image characterized by raw measurements S.sub.p(i,j) associated with the active bolometers B.sub.pix_(i,j).

(21) The method according to the present invention comprises a step a) of calculating the electrical resistances R.sub.Tc(i,j) and R.sub.Tc(k), at the temperature T.sub.amb, of the active and blind bolometers B.sub.pix_(i,j) and B.sub.b_(k), respectively.

(22) These electrical resistances are in particular calculated from the respective electrical resistances R.sub.Tr(i,j) and R.sub.Tr(k), of said bolometers, at a reference temperature T.sub.r, said resistances being stored in the memory of the computer.

(23) The electrical resistances R.sub.Tr(i,j) and R.sub.Tr(k) of the active bolometers B.sub.pix_(i,j) and of the blind bolometers B.sub.b_(k), respectively, at the reference temperature T.sub.r, may be determined prior to step a), in a step a1).

(24) For example, a step a1) is executed during the manufacture of the imager.

(25) Step a1) then comprises a first substep a1.sub.1) of determining the electrical resistances of the reference temperature of each of the active bolometers B.sub.pix_(i,j).

(26) The first substep a1.sub.1) employs a mask kept at the reference temperature T.sub.r and placed in front of the imager 1 (it will be understood that the imager is also kept at the reference temperature T.sub.r).

(27) The current flowing through each of the active bolometers B.sub.pix_(i,j) is then measured individually.

(28) In particular, the measurement of the current I.sub.pix_(a,b) of a given active bolometer B.sub.pix_(a,b) comprises closing the switching device connecting it to the common line BL(b), the other switches being kept open. The switches GSK associated with the blind bolometers are also kept open so as to cancel out the current capable of flowing therethrough.

(29) The equivalent circuit diagram resulting from this configuration is shown in FIG. 4a.

(30) The voltage V.sub.CTIA at the output S of the capacitive transimpedance amplifier CTIA associated with column “b” respects the following relationship (1):

(31) $\begin{array}{cc}{V}_{\mathrm{CTIA}}=V_{\mathrm{BUS}}+\frac{T_{\mathrm{int}}}{C_{\mathrm{int}}}.Math.I_{\mathrm{pix}\_}\left(a,b\right)& \left(1\right)\end{array}$

(32) C.sub.int being a capacitance of the amplifier CTIA and T.sub.int an integration time in the step of measuring the current I.sub.pix_(a,b).

(33) Moreover, the current I.sub.pix_(a,b) is dependent on the geometric and electrical characteristics of the bolometer and on the characteristics controlling the latter.

(34) More particularly, the current I.sub.pix_(a,b) also respects the following relationship (2):

(35) $\begin{array}{cc}{I}_{{\mathrm{pix}}_{-}}\left(a,b\right)=\frac{1}{2}.Math.k_n.Math.\frac{W}{L}.Math.{\left(\mathrm{GFID}-R_{\mathrm{Tr\_}}\left(a,b\right).Math.I_{\mathrm{pix}\_}\left(a,b\right)-V_{\mathrm{th},N}\right)}^2& \left(2\right)\end{array}$ μn being the electron mobility in the material forming the bolometer in question; C.sub.ox being the capacitance per unit area of the gate of the transistor controlling the bolometer; k.sub.n=μn. C.sub.ox being an NMOS gain factor; W/L being the width-to-length ratio of the channel of the transistor controlling the bolometer; and V.sub.th,N being the threshold voltage of the NMOS transistor controlling the bolometer.

(36) The reference electrical resistance R.sub.Tr(i,j) at the reference temperature T.sub.r is thus deduced from relationships (1) and (2).

(37) Step a1) then comprises a second substep a1.sub.2) of determining the electrical resistances, at the reference temperature, of each of the blind bolometers B.sub.b_(k).

(38) Substep a1.sub.2) is similar to substep a1.sub.1).

(39) In particular, the second substep a1.sub.2) also employs the mask kept at the reference temperature T.sub.r and placed in front of the imager 1 (it will be understood that the imager is also kept at the reference temperature T.sub.r).

(40) The current flowing through each of the blind bolometers B.sub.b_(k) is then measured individually.

(41) In particular, the measurement of the current I.sub.b_(l) of a given blind bolometer B.sub.b_(l) comprises closure of the transistor GSK controlling the latter in order to connect it to the common line BL(l), the other switches being kept open.

(42) The equivalent circuit diagram resulting from this configuration is presented in FIG. 4b.

(43) The voltage V.sub.CTIA at the output S of the capacitive transimpedance amplifier CTIA associated with the column “I” respects the following relationship (3):

(44) $\begin{array}{cc}{V}_{\mathrm{CTIA}}=V_{\mathrm{BUS}}+\frac{T_{\mathrm{int}}}{C_{\mathrm{int}}}.Math.I_{b\_}\left(l\right)& \left(3\right)\end{array}$

(45) Moreover, the current I.sub.b_(l) depends on the geometric and electrical characteristics of the bolometer and on the characteristics controlling the latter.

(46) More particularly, the current I.sub.b_(l) also respects the following relationship, relationship (4):

(47) $\begin{array}{cc}{I}_{b_{-}}\left(l\right)=\frac{1}{2}.Math.k_p.Math.\frac{W}{L}.Math.{\left(V_{\mathrm{th},P}+\mathrm{VSK}-R_{\mathrm{Tr\_}}\left(l\right).Math.I_{\mathrm{b\_}}\left(l\right)\right)}^2& \left(4\right)\end{array}$ μ.sub.p being the hole mobility in the material forming the bolometer in question; C.sub.ox being the capacitance per unit area of the gate of the transistor controlling the bolometer; K.sub.p=μ.sub.p. C.sub.ox being a PMOS gain factor; W/L being the width-to-length ratio of the channel of the transistor controlling the bolometer; and V.sub.th,P being the threshold voltage of the PMOS transistor controlling the bolometer.

(48) The reference electrical resistance R.sub.Tr(1) at the reference temperature T.sub.r is thus deduced from relationships (3) and (4).

(49) The determination of the reference electrical resistances R.sub.Tr(i,j) and R.sub.Tr(k) thus employs components usually integrated into an imager. In other words, it is not necessary to modify the imager in order to implement the method according to the present invention.

(50) The calculation of the electrical resistances at the ambient temperature T.sub.amb may then involve an activation energy E.sub.a representative of the material forming each of the active and blind bolometers B.sub.pix_(i,j) and B.sub.b)(k).

(51) More particularly, the electrical resistances R.sub.Tamb(i,j) and R.sub.Tamb(k) are calculated using the following relationships:

(52) $\begin{array}{cc}{R}_{\mathrm{Tamb}}\left(i,j\right)=R_{\mathrm{Tr}}\left(i,j\right).Math.e^{\frac{{\mathrm{qE}}_a}{k}\left(\frac{1}{T_{\mathrm{amb}}}-\frac{1}{T_r}\right)}& \left(5\right)\\ \mathrm{and}& \\ R_{\mathrm{Tamb}}\left(k\right)=R_{\mathrm{Tr}}\left(k\right).Math.e^{\frac{{\mathrm{qE}}_a}{k}\left(\frac{1}{T_{\mathrm{amb}}}-\frac{1}{T_r}\right)}& \left(6\right)\end{array}$

(53) The method according to the present invention also comprises a step b) of determining the temperatures T.sub.sc(i,j) actually measured by each of the active bolometers B.sub.pix_(i,j) based on the electrical resistances calculated in step a) and on the raw measurements S.sub.p(i,j).

(54) In particular, the temperature T.sub.sc(i,j) actually measured by an active bolometer B.sub.pix_(i,j) respects the following relationship (7):
S.sub.P(i,j)=Resp(T.sub.amb,i,j)T.sub.sc(i,j)−T.sub.amb)+S.sub.0,T.sub.amb(i,j)  (7)

(55) where: Resp(T.sub.c,i,j) is the responsivity of the bolometer; S.sub.0,Tamb(i,j) is the value output by the active bolometer B.sub.pix_(i,j) for a temperature actually measured equal to the ambient temperature.

(56) In this respect, the value S.sub.0,Tamb(i,j) associated with an active bolometer B.sub.pix_(i,j) of a column C.sub.j is dependent on the difference between the currents I.sub.0,pix(i,j) and I.sub.0,b(j) capable of flowing through said active bolometer B.sub.pix_(i,j) and the blind bolometer B.sub.b_(j) with which the column Cj is associated, respectively, for a temperature actually measured equal to the ambient temperature.

(57) In other words, for each of the active bolometers, the term S.sub.0,Tamb(i,j) respects the following relationship, relationship (8):

(58) $\begin{array}{cc}{S}_{0,T_{\mathrm{amb}}}\left(i,j\right)=\mathrm{VBUS}-\frac{T_{\mathrm{int}}}{C_{\mathrm{int}}}.Math.\left(I_{0,b\left(j\right)}-I_{0,\mathrm{pix}\left(i,j\right)}\right)& \left(8\right)\end{array}$

(59) the currents I.sub.0,pix(i,j) and I.sub.0,b(j) depending on the electrical resistances R.sub.Tamb(i,j) and R.sub.Tamb(j), respectively.

(60) It is therefore possible to deduce, from relationships (7) and (8), the temperature T.sub.sc(i,j) actually measured by each of the bolometers, using the following relationship:

(61) $\begin{array}{cc}{T}_{\mathrm{sc}\left(i,j\right)}=\frac{S_{P_{\left(i,j\right)}}-S_{0,T_{\mathrm{amb}\left(i,j\right)}}}{{\mathrm{Resp}}_{\left(i,j\right)}}+T_{\mathrm{amb}}& \left(9\right)\end{array}$

(62) The processing thus carried out on the raw image allows a temperature-compensated final image that is free from pixelization effect and columnar aspect to be obtained.

(63) The present invention also relates to a computer program that, when it is implemented by a computer, allows the processing method according to the present invention to be executed.

(64) The invention furthermore relates to an imager provided with active bolometers B.sub.pix_(i,j) arranged in a matrix array of n rows L.sub.i and m columns C.sub.j; blind bolometers B.sub.b_(k), each blind bolometer P.sub.b_(k) being employed for the differential measurement of the active bolometers B.sub.pix_(i,j) of at least one column of bolometers that is specific thereto, each blind bolometer B.sub.b_(k) advantageously being associated with a single column (C.sub.j) of active bolometers B.sub.pix_(i,j); a computer equipped with the computer program.

(65) Lastly, the invention also relates to a method of using the imager according to the present invention for detection, in particular the detection of people, in a room.