WO2003073751A1 - Suppression du bruit dans un reseau de detecteurs infrarouges - Google Patents

Suppression du bruit dans un reseau de detecteurs infrarouges Download PDF

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Publication number
WO2003073751A1
WO2003073751A1 PCT/GB2003/000768 GB0300768W WO03073751A1 WO 2003073751 A1 WO2003073751 A1 WO 2003073751A1 GB 0300768 W GB0300768 W GB 0300768W WO 03073751 A1 WO03073751 A1 WO 03073751A1
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WIPO (PCT)
Prior art keywords
line
noise
signal
detectors
channel
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PCT/GB2003/000768
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English (en)
Inventor
Derik Mckenzie Thomson Cochrane
Original Assignee
Qinetiq Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Qinetiq Limited filed Critical Qinetiq Limited
Priority to AU2003215724A priority Critical patent/AU2003215724A1/en
Publication of WO2003073751A1 publication Critical patent/WO2003073751A1/fr

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/60—Noise processing, e.g. detecting, correcting, reducing or removing noise
    • H04N25/67—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to fixed-pattern noise, e.g. non-uniformity of response
    • H04N25/671—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to fixed-pattern noise, e.g. non-uniformity of response for non-uniformity detection or correction
    • H04N25/677—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to fixed-pattern noise, e.g. non-uniformity of response for non-uniformity detection or correction for reducing the column or line fixed pattern noise
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/20—Cameras or camera modules comprising electronic image sensors; Control thereof for generating image signals from infrared radiation only
    • H04N23/23—Cameras or camera modules comprising electronic image sensors; Control thereof for generating image signals from infrared radiation only from thermal infrared radiation

Definitions

  • This invention relates to a method and apparatus for noise suppression in infra red detector arrays.
  • the arrays may have detectors of pyroelectric, resistance bolometers, and cooled CdHgTe materials.
  • Pyroelectric detector arrays are useful in thermal imaging cameras such as those used by the emergency services.
  • smoke filled buildings they enable users to negotiate within buildings and locate people and sources of fire.
  • Such cameras focus a series of infra red images onto an array of pyroelectric detector elements, whose collective output is displayed on a video screen for viewing by an operator.
  • In low light levels it becomes important to provide as clear a picture as possible on the screen because the detectors are operating near performance limits. Any noise in the system degrades the observable picture.
  • method of reducing low frequency lines noise from a thermal image processor includes the steps of: imaging thermal energy from a scene onto a detector, reading detector outputs to form a succession of line signals collectively forming a frame, processing each line signal to form a video signal representing a visible image of the thermal scene for display on a screen,
  • noise processing channel A time integrate signals from the blanked off detectors and subtract this from the present signal to leave white noise and low frequency noise signals; calculate average line noise level at the left and right blanked off sections the line; calculate the best fit line for the line noise in each line signal taking into account its slope over the complete line period to form a line slope noise signal;
  • a thermal imaging processor for processing a thermal image for display on a screen includes: - means for imaging thermal energy from a scene onto a detector array, means for reading detector outputs to form a succession of line signals, processing means for processing each line signal to form a video signal representing a visible image of the thermal scene for display on a screen,
  • means in the noise processing channel A for time integrating signals from the blanked off detectors and subtract them from a current signal to leave white noise and low frequency noise signals; means for calculating average line noise level at the left and right blanked off detectors; means for calculating the best fit line for the line noise taking into account its slope over the complete line period to form a noise slope line signal;
  • the detector array may be an array of ferroelectric thermal detectors, or resistance bolometers, or a single or group of line photo detectors with optical scanning.
  • the number of detectors blanked off at both ends of each line may be 8, 16, 32 or other convenient digital number to simplify processing.
  • a sporadic low-frequency noise signal exists at the analogue output of the present generation of UK uncooled ferroelectric arrays.
  • the origin of this noise signal is not known but its effect is observable as a low-frequency first order slope superimposed on to the actual thermal imaging response signals and natural white noise on each video line of the displayed image.
  • thermal image information is extracted by taking the difference between two fields of array information using a thermal reference shutter known as a chopper.
  • This process termed Image Difference Processing (IDP)
  • IDP Image Difference Processing
  • a low-frequency noise signal remains and can be readily perceived as fluctuations in the image with a line structure. This can be confirmed by viewing adjacent lines of video information on an oscilloscope trace, revealing that the noise structure has high frequency components but mainly varies over the line period with an approximately first order linear slope.
  • the 'line noise' signal has relatively low amplitude (similar to the white noise) and does not severely degrade the overall image quality, its effect is undesirable and distracting to the viewer.
  • This problem exists on the silicon IC designs for two known thermal detector arrays. The operation of the silicon IC in these array formats has been validated using hybrid detector technology and will eventually enter mass production volumes when the integrated detector technology matures. In order to avoid a costly silicon redesign and revalidation process, it would be preferable to employ a corrective algorithm within the image processing electronics to suppress the effect of the unwanted noise signal.
  • the method of this invention provides a line noise suppression technique that has been successfully demonstrated using a prototype thermal imaging camera. This technique provides an inexpensive solution to the line noise problem with ferroelectric arrays but could also benefit other imaging systems with similar line noise problems. Thermal cameras employing scanning of an image onto a single detector or a single line of detectors may also benefit from the invention.
  • Figure 1 is a block diagram of ferroelectric array image processing to provide a video output signal
  • Figure 2 shows an array of ferroelectric detectors
  • Figure 3 is a flow diagram of a line noise suppression algorithm.
  • Figure 4 is an infra red image using a thermal imaging camera without the noise cancelling algorithm
  • Figure 5 is the image of Figure 4 with the algorithm in operation
  • Figure 6 is an infra red image using a thermal imaging camera without the noise cancelling algorithm
  • Figure 7 is the image of Figure 6 with the algorithm in operation;
  • Figure 1 shows the processing of a thermal image into a video signal for display on a video screen such a liquid crystal display screen or a cathode ray tube screen.
  • An infra red (IR) scene S is imaged through a lens 1 on to a detector array 2.
  • IR infra red
  • a detector array 2 typically this will be an x,y matrix of 384 x 288 pyroelectric detectors, each detector forming one pixel in a displayed image. Pyroelectric detectors measure temperature differences. To do this each one is alternately exposed to IR in the scene S and a reference temperature provided by the blades 3 of a rotating shutter, controlled by a chopper motor 4.
  • Each detector in the array 2 is read out sequentially through a buffer and demultiplex unit 5 to give a string of voltage levels in successive time intervals. Each voltage level represents the amount of IR received by each detector in a frame time. The frame time is the time taken to read the whole array 2.
  • the array output is amplified by a channel gain amplifier 6 so that the dynamic range matches the input range of a following analogue to digital converter (ADC) 7.
  • ADC analogue to digital converter
  • the digitised signal is then processed in a programmable logic device (PLD) 8 as described below, and converted back to an analogue signal in a DAC 9 for supply to a video monitor 10.
  • PLD programmable logic device
  • the standard digital processing includes the steps of:
  • an image difference processor (IDP) 11 this compares the current signal level from a given detector with that of the reference level (a signal emitted from the chopper blades 3) stored in memory 12.
  • the algorithm of the present invention operates between the IDP 11 and gain correction 13. This algorithm exploits the fact that the line noise signal varies slowly over the duration of a video line with an approximately first order slope. By taking a measure of the noise offset at either end of the video line it is possible to compute the theoretical first order slope of the line noise over the intervening data points. The computed slope can then be subtracted from each data pixel on the active portion of the line, restoring the thermal image information to a normalised average.
  • the algorithm requires a small section of the left and right sides of the active array 20 to be masked to prevent differential thermal image information breaking through and thus offsetting the algorithm, see Figure 2 where 8 detectors 21 , 22 at both ends of each line are masked. Other numbers could be chosen, e.g. 16 (twice) detectors, but these decrease the number of active detectors and reduce horizontal field of view.
  • the optical mask solution is not ideal however since a small amount of shadowing is observed at the edges of the mask, requiring a larger area to be obscured for correct operation of the algorithm (and thus a greater reduction in the active field of view).
  • the preferred masking solution may be achieved electrically by altering one of the metalisation layers of the silicon readout IC during fabrication to effectively short-circuit the left and right sections of the pixel array to the reset voltage state.
  • the algorithm steps are shown in Figure 3 and operate on a line signal one line at a time.
  • Step 1 Divide a Line N raw pixel data signal into a noise processing channel A and a delay channel B.
  • This line signal is the IDP 11 output of each detector in a line with each line read sequentially.
  • the time taken to read all detectors in one line is a line time, and time for all lines to be read is a frame time.
  • Step 2 Time integrate 25 each detector output. This provides an average amplitude value for each detector.
  • Step 3 Subtract 26 time integrated detector value from current value to give a signal having white noise and low frequency (LF) noise only.
  • Step 4 Calculate 27 the average line noise level at the left and right blanked- off sections of the line by summing together the noise signals from the 'blind' eight detectors and then divide by eight to remove the white noise. Output a left and a right LF noise offset signal. Note that this process can be performed with a simple binary divide (i.e. right shift 3) rather than employing complicated division arithmetic logic.
  • Step 5 Calculate 28 the best fit line for the line noise taking into account its slope over the complete line period to form a line slope noise signal. Output a Line - ⁇ LF noise slope signal.
  • Step 6 Delay 29 each line of data as they pass through the noise slope calculation algorithm and feedback through the main processing pipeline for correction. Output a raw pixel data signal.
  • Step 7 Combine 30 channels A and B and subtract the slope line noise component from each data point on the active portion of the line. Output a Line N -1 pixel data with LF noise suppression.
  • Step 8 Repeat for every line in the current field, a complete frame.
  • Steps 1-8 are repeated for successive frames.
  • Figure 4 is a thermal image of a person processed without use of the algorithm. Several horizontal lines can be seen particularly across the shirt of the person. This is a snapshot, the position of the lines change with time because they represent noise in the system.
  • Figure 5 is a thermal image with the algorithm in operation; note that the horizontal lines are now missing.
  • Figure 6 is a thermal image of electrical leads hanging on a wall. Note several horizontal lines.
  • Figure 7 is the same image as in Figure 6 but with the algorithm in operation; note the lack of horizontal lines.
  • the algorithm may be implemented in hardware, e.g. in a programmable logic device or frozen in an A.S.I.C. design, or instructional software steps incorporated in a recording and storage medium such as a memory chip or disk.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Transforming Light Signals Into Electric Signals (AREA)

Abstract

Cette invention a trait à une technique ainsi qu'au dispositif correspondant permettant de supprimer le bruit dans un réseau de détecteurs infrarouges par suppression du signal de bruit de basse fréquence Ce bruit est observable sous la forme d'une courbe de premier ordre de basse fréquence se superposant aux signaux de réponse d'imagerie thermique en cours ainsi que sous la forme d'un bruit blanc naturel dans chaque ligne vidéo de l'image affichée. Il est possible d'utiliser la technique selon l'invention sur des réseaux de détecteurs ferroélectriques, des réseaux de détecteurs à bolomètre à résistance ou des réseaux de détecteurs infrarouges à balayage unique ou en ligne. On désactive plusieurs détecteurs placés aux deux extrémités de chaque ligne de détecteurs afin de les empêcher de recevoir un quelconque rayonnement infrarouge. Chaque signal de ligne est réparti en un canal de processeur de bruit (A) et en un canal de ligne de retard (B). Dans le canal A, les sorties de ces détecteurs désactivés sont traitées de façon à donner la courbe de bruit de chaque signal de ligne. Dans le canal B, chaque signal de ligne est temporisé par le retard total du canal A. Le signal de pente de bruit de chaque ligne est soustrait de son signal de ligne temporisé associé.
PCT/GB2003/000768 2002-02-28 2003-02-19 Suppression du bruit dans un reseau de detecteurs infrarouges WO2003073751A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2003215724A AU2003215724A1 (en) 2002-02-28 2003-02-19 Noise suppression in infra red detector arrays

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0204697.7 2002-02-28
GB0204697A GB2386018A (en) 2002-02-28 2002-02-28 Noise reduction in infra-red imaging arrays using shielded detectors

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GB (1) GB2386018A (fr)
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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008062287A1 (fr) * 2006-11-23 2008-05-29 Sicpa Holding S.A. Utilisation d'équipements de détection d'empreintes pour l'authentification d'articles en feuille
US7767963B1 (en) 2006-12-08 2010-08-03 Draeger Safety, Inc. Thermal imaging camera internal damping system
WO2010123428A1 (fr) * 2009-04-22 2010-10-28 Flir Systems Ab Procédé de traitement d'image pour supprimer un bruit de colonne ou de rangée spatiotemporel
US11012647B2 (en) 2017-02-22 2021-05-18 Flir Systems, Inc. Low cost and high performance bolometer circuity and methods

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FR2686472A1 (fr) * 1992-01-17 1993-07-23 Thomson Tubes Electroniques Procede d'elaboration d'une image matricielle avec comparaison globale de lignes de piscels et reduction du bruit correle en ligne.
US5861913A (en) * 1995-12-15 1999-01-19 Nec Corporation Heat-sensitive infrared-light image sensor with circuitry for canceling temperature-dependent drift components
WO1999051024A1 (fr) * 1998-03-28 1999-10-07 The Secretary Of State For Defence Traitement d'image ameliore
EP0954170A2 (fr) * 1998-04-30 1999-11-03 Picker International, Inc. Dispositif de prise de vues à rayons X
WO2001036926A1 (fr) * 1999-11-15 2001-05-25 Sarnoff Corporation Ensemble detecteur infrarouge non refroidi presentant une stabilite de temperature amelioree et reduction du bruit stable

Family Cites Families (3)

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Publication number Priority date Publication date Assignee Title
US5659355A (en) * 1994-10-31 1997-08-19 Eastman Kodak Company CCD dark mean level correction circuit employing digital processing and analog subtraction requiring no advance knowledge of dark mean level
JPH1023335A (ja) * 1996-07-05 1998-01-23 Nec Corp 赤外線撮像装置
JP2001042042A (ja) * 1999-07-27 2001-02-16 Canon Inc 撮像装置

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2686472A1 (fr) * 1992-01-17 1993-07-23 Thomson Tubes Electroniques Procede d'elaboration d'une image matricielle avec comparaison globale de lignes de piscels et reduction du bruit correle en ligne.
US5861913A (en) * 1995-12-15 1999-01-19 Nec Corporation Heat-sensitive infrared-light image sensor with circuitry for canceling temperature-dependent drift components
WO1999051024A1 (fr) * 1998-03-28 1999-10-07 The Secretary Of State For Defence Traitement d'image ameliore
EP0954170A2 (fr) * 1998-04-30 1999-11-03 Picker International, Inc. Dispositif de prise de vues à rayons X
WO2001036926A1 (fr) * 1999-11-15 2001-05-25 Sarnoff Corporation Ensemble detecteur infrarouge non refroidi presentant une stabilite de temperature amelioree et reduction du bruit stable

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008062287A1 (fr) * 2006-11-23 2008-05-29 Sicpa Holding S.A. Utilisation d'équipements de détection d'empreintes pour l'authentification d'articles en feuille
EA016635B1 (ru) * 2006-11-23 2012-06-29 Сикпа Холдинг С.А. Способ аутентификации объекта в виде листа и система
US7767963B1 (en) 2006-12-08 2010-08-03 Draeger Safety, Inc. Thermal imaging camera internal damping system
WO2010123428A1 (fr) * 2009-04-22 2010-10-28 Flir Systems Ab Procédé de traitement d'image pour supprimer un bruit de colonne ou de rangée spatiotemporel
US8737760B2 (en) 2009-04-22 2014-05-27 Flir Systems Ab Image processing method for suppressing spatio-temporal column or row noise
US11012647B2 (en) 2017-02-22 2021-05-18 Flir Systems, Inc. Low cost and high performance bolometer circuity and methods

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Publication number Publication date
GB0204697D0 (en) 2002-04-17
AU2003215724A1 (en) 2003-09-09
GB2386018A (en) 2003-09-03

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