CA2130337C - Method and apparatus for dynamic correction of microscopic image signals - Google Patents
Method and apparatus for dynamic correction of microscopic image signalsInfo
- Publication number
- CA2130337C CA2130337C CA002130337A CA2130337A CA2130337C CA 2130337 C CA2130337 C CA 2130337C CA 002130337 A CA002130337 A CA 002130337A CA 2130337 A CA2130337 A CA 2130337A CA 2130337 C CA2130337 C CA 2130337C
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- CA
- Canada
- Prior art keywords
- offset correction
- correction factors
- light
- image signal
- charge coupled
- Prior art date
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Classifications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
- H04N1/40—Picture signal circuits
- H04N1/401—Compensating positionally unequal response of the pick-up or reproducing head
Abstract
A circuit for correcting an image signal received from a camera (102) which includes a plurality of charge coupled devices (102) each for providing a light (112) signal indicative of the intensity of light incident thereon; the plurality of light signals are indicative of an image received by the camera (102). A correction circuit (212) includes: a gain memory (206) for storing a plurality of gain correction factors each associated with a respective charge coupled device, and an offset memory (214) for storing a plurality of offset correction factors each associated with a respective one of the plurality of charged coupled devices (102). The gain memory (206) is responsive to a control circuit (210) for multiplying (208) the plurality of electric signals by the appropriate gain correction factor. Similarly, the offset memory (214) is responsive to a control circuit (210) for adding (216) the appropriate one of the plurality of offset correction factors with the signal from its respective charge coupled device (102).
Description
~W093/16551 PCT/US93/01442 ' ~3032~
Description NETHOD ~D ~PP~RATUS FOR DYNAMIC CO~REC~ION
OF MIC~08COPIC T~
:' Technical Field The present invention is directed toward - apparatus for providing signals representing an : lO image of an object and, more particularly, toward method and apparatus for dynamically correcting I
image signals for variations in the illumination of the image or the detection of the image by the camera.
; lSBack~round of the Invention Systems for providing image signals typically ' include a camera positioned to be focused upon an object and con~tructed for providing image signals representing an~image of the object. Typically, 20 ~ ~ these syst~ms include cameras having an array of discrete charge coupled devices ("CCD "), referred o as pixels, for providing electrical signals wherein the magnitude of the electrical signal is indicative~of the intensity of light in ident upon 25~ each pixelO ~By properly timing the man~er that the plurality of~:signals are obtained from the camera, the plurality~of signals can be:used to represent an image of an object upon which the camera is focused.
However,~several factors contribute to fixed ~pattern variations of the plurality of discrete ;~pixel elem2nts imaged by the camera. One factor, referred to: herein as illumination variation, results from nonuniformity in illlt~in~tion caused by ~:: optical element imperfections, dust collection r and 35- positioning variations. Another factor, referred to herein as CCD variation, results from two types of imperfections in the performance of the CCDs. One ~ :performance imperfection results from size tolerance :
W093/165~1 PCT/USg3/01~4~2 ~303~ - 2 -variations on the active area sensitive to light for each pixel. These size imperfections result in sensitivity variations between pixels on a given sensor that are mathematically eguivalent to illumination variation. Illumination ~ariation, whether caused by nonuniformity in illumination or by CÇD size variations are corrected for using gain correction.
Another factor that contributes to fixed pattern variations is also caused by CCD performance imperfections. This factor is referred to as offset variation and is caused by the dark current signal within the CCD, i.e., the current signal that is present at the CCD when no light is incident on the CCD. The offset variation is determined as the magnitude of the signal from a pixel when no light is inc:ident upon the pixel. Illumination variation and offset variation present ~hemselves as two types of errors in~the resulting signal from each pixel.
20 ~ It is~dasirable, therefore, to provide method and~ apparatus for correcting image~ signals from a camera for i~ rin~tion variation, resulting from nonuni~ormity in illumination and from CCD size variation.~ It~is~ also desirable to provide method 25~ and ~pparatus for~ correcting image signals from a camera for offset variation resulting from CCD dark current Further, in order to obtain a plurality of signals from the array of pixel elements that most ~ accurately represent an image of the object, it is : ' :
~' necessary to correct each pixel for the above mentioned variations in offset and illumination.
~ost prior art systems for collecting image signals have attempted to provide data processing methods for correcting the plurality of signals. However, these methods cannot be performed at the same speed W093/165S1 213 ~ 3 ~ 7 PCT/US93/01442 that the si~nals are obtained from the camera and, therefore, introduce significant delay in the time required to obtain an image signal. Further, these methods are also not accurate. Accordingly, it is ~: 5 desirable to provide method and apparatus for ;: correcting a plurality of signals from a CCD camera wherein the correction can be made rapidly while the plurality of signals are obtained from the camera and wherein the correction is made prior to the lo analog-to-digital conversion, to utilize the maximum number of quantization steps to measure signal levels. - .-Summary of the Invention The:present invention comprises a circuit for 15:~ ~ real time corr~ction of an image signal provided by a~camera wherein the image signal represents the image~ of an~ object. The camera: may include a plurality of charge coupled devices for providing a respective~ plurality of pixel signals wherein the ~ plurality of:pixel signals combine to provide the image signal. ~The circuit of the subject invention nGludes memory ~or storing ~a plurality of ~ correction factors wherein each~of:the plurality of C~ corre tion:factors is associated:~with a:~respective 25~ one of the plurality of charge coupled devices. The oircuit also ~includes signal processing ~eAn~ for combining ~each of~ the plurality; of ~correction factors with the respective one of the plurality of ,~,, ~ , pixel signals with which it is associated. In a 30~ first presently preferred embodiment of the ~ ~: ; : invention, the correction factors are related to the incident, ' unmodulated light and gain of the individual charge coupled devices and the signal processing circuit is a circuit: constructed to multiply the correction factors by the plurality of pixel signals. In a second presently pr~ferred 2~3033~ ..
embodiment of the invention, the correction factors are offset correction factors associated w~th the of~sets of the plurality of charge coupled devices and the signal processing circuit is an adder for adding the plurality for offset correction- factors to the plurality of pixel signals.
In still another embodiment of the invention, . :
the apparatus includes a light assembly for providing light to illuminate the object and for ~ providing a light signal 1ndicative of the intensity of the light.~ The signal processing circuit is further responsive to the light signal for altering the reference~and offset factors so that the image signal is corrected for variations in the intensity 15~ of~the light~
Brief Descri~t~ion of the Drawings Figure I is an ilIustrative diagram of a camera~ system~ constructed in accordance with the pre~sent invention; and ~ ~
20~ . Figure ~2 is a more detailed illustrative diagram~of~the~daea~processor illustrated in Figure Detailed~Description of the Invention ~
e~ subject invention-~provides~ method and 25~ appa}atus for dynamically correcting ~image signals from a camera for~fixed pattern variation in gain, illumination, ~and offset. A camera systém lO0 is illustrated~ in ~Figure l. The camera system lO0 includes a CCD camera 102~ for providing an image ~ signal representing the image of an object. As an example, the camera system lO0 may be a camera system for obtAin;ng and analyzing medical specimens. However, those skilled in the art Will appreciate~that the subject invention is applicable 35 ~ to camera systems 100 constructed for obtaining the - image signal of a wide variety of transmissive : ~ :
~,WO93~16551 2 1 3 ~ 3 3 ~ PCT/US93/01442 objects.
~; The slide 10~ is mounted to a motion ~ controller-106;that provides a scan signal to a data ',~ - processor 108 to indicate that the slide 104 is ~'5 ~ being moved into position for an image to be ; obtained. ~ The motion controller 106 may comprise any of a~ variety of suitable devices readily available to those~skilled in the art.
An illuminat~ion system 112 includes a strobe 10~ ~ light 114, ~a~photodetector sensor 116, and a beam splitter~118. ~The illumination system 112 may also include collector~and~projection optics 113, a lens and~aperture 115, and a condenser lens and aperture 117,~disc~lese~in more;detail below. ~The strobe 15~ 1ight ~114 is~responsive to a~flash signal received Pr;om~the data~proceccor 108 for providing~a flash of light.~The~ L ~ light 114 is also~responsive to "~ an~intensi ~ signal~for varying the~intensity of the flash~of light~provided. The data~procec~or 108 is 2;0~ O~ngive~to~the,~,scan signal for~synchronizing the oaméra~,~102~and ,the~ LIobe~;light~114~to~ gather the ,image~ Suitable,~strobe lights~ ll4 for~ operation the'~ subject~invention~as~dèscribed~,herein may r~ l'y~sel'e~ted~by:those::skilI;ed~:~in:the art from 25~ a~- variety~of~strobe~ lights~that-~are commercially avai~lable.~ r~hèr,~ it will~be~apparent to those skilled~ in~,~the art ~that, although ~'the present invention :iS described-by reference to a strobe light 114,~for~provlding a flash of light, other 30~ devices~ constructed to provide ~a continuous source ~ of light ~may~bé readily~ substitu~ted there for n,~ 'without departing from the true s~cope and spirit of the subject~invention.
The~phot d etector sensor ll6 is constructed ;35~ to receive~a;portion of the flash of light from the stro~e light~ll4~via a beam splitter 11~. The beam ~,, :
WOg3/165~1 PCT/US93/01442 2~ 3~ - 6 -splitter 118 may comprise any of a variety of devices co~r~rcially available for splitting a beam of light into component parts. The photodetector sensor 116 is constructed to provide a light signal indicative of the intensity of light provided by the strobe light 114. The light signal is coupled to the data processor 108 and is used for correcting the image signal received from the camera 102, as will be described in more detail below.
.
lo The collector and projection optics 113, the lens and aperture 115, and the condenser lens and aperture ~I17 are each provided for optically tr~n~m;tting the flash of light from the strobe light 114 to the photodetector sensor 116 and the ; I5 slide 104. Standard elements appropriate for optically transmitting the flash of light are commercially available and may be readily selected by those skilled in the art~ Additionally, it will ;be~ apparent~ to those skilled~ in the art that ';20~ alternative arrangements for optically transmitting the flash of light from the strobe light 114 to the photodetector sensor 116 and the slide 104 may be provided without departing from the~scope and spirit of the subject invention. ~ ~
25 ~ The càmera 102 may comprise a video camera ncluding a~plurality of charge coupled devices for ;providing ~a plurality of signals wherein the plùrality of signals may ~e combined to provide the ' ' image signal to the data processor 108. As is known in the art,~the plurality of charge coupled devices, also referred to as pixel elements, each provide a signal indicative of the intensity of light incident thereon. However, since the plurality of pixel elements are discrete one from another, they each 3~ have slightly different gain and offset characteristics that introduce minor inaccuracy in ~' :
PCTIUS93/01~ ~2 ~ 13 o 3 3 t,7 lPEA/us 2 2 APR 199 the re~ulting image qignals. Additionaliy the unmodulated illumination incident on the CCD pixel~
is nonuniform and, therefore, further reduces the ~~accuracy of the resulting image ~ignals.
Accordingly, the data processor 108 includ2s circuitry for correcting the plurality of signals received from the pixel elements of~t~e camera lO2 for ~ariation in offqet, gain, and illumination nonuniformity between pixel elements.
10: A suitable correction circuit 200 i~
llu~trated in Figure 2. The circuit 200 includes an amplifier 202 for receiving and amplifying the ~;; image :signal provided.by the camera 102. The :~: : amplifier 202 i9 coupled to a gain correction ~: 15circui~ 204 for correcting the image si~nal for pixel-to-pixel variation in gain and illumination.
The gain correction circuit 204 includes a gain unit 206 coupled to a multip.lication circuit 208 and : re~ponqive to timing and control 8ignal9 received 20: from a control circuit 210 for multiplying the image iy~al by a~plurality of predetermined gain factors.
The gain uni~ 206 co~ Lise a memory unit 205 : coupled:to a digital-to-analog converter 207 for providing analog correction 3ignal to the : 25~mu}tiplication circuit 208. The memory 205 i8 selected ~o 3tore predeter~i~e~ cG~ction factor3.
; ~ ~
The digi~al-to-analog con~er~er 207 i~ ~caled ~o : that it~ ~t~p re~olution i5 les than that of ~he analog-to-digital converter 222. Thi3 allow~ the 30correc~io~ to be placed rea30nably cen~ered within ~: , the analo~-to-digital converter step size and results i~ accurate correction~without sacrificing the dynamic range of the analog-to-digit~l con~erter 222.
35A~ discussed aboYe, the image ~i~nal includes ~:~ a plurality of signals obt~; n~ from an array of ~ r~l~F~sH~ET
~13D~7 Pcr/JS 9 33 / o ~
IPEA/US 2 ? APR 1994 di3crete charge coupled devic~, or pixel elements, of the camera 102. - A~ al90 discu~3ed above, the gain and incident illumination of the pluraIity of ~ charge coupled device~ may vary slightly.
s Accordingly, a plurality of gain corr~ction factorq are stored in the memory 205 of the gain unit 206, each a~sociated with a respective charge coupled de~ice of the camera 102. The control circuit 210 provides timing and control signal~ to the gain unit 206 so that each gain factor i9 multiplied by it~
respective portion of the image qignal in the multiplier 208,;thereby correcting each respective portion of the image signal for any varia~ion in it~
respective charge coupled device or incident illumination and, thereby, substantially eiiminating undesirable effects o~ gain variation or illumination nonllniformity from the re~ulting image ~ignals.
Similarly, an offqet correction circuit 212 :include.c an off et unit 21~ including an offset memory 213: for ~toring a plurality of offset : correction factor~,~ each associated with a :: respecti~re one of the plurality of charge coupled : device3 of the ~amera 102, and a digital-to-analog 25~ co~lvert~r 215. The offset correction circuit 212 includ~s an adder 216 for adding the image signal ; ~ ~rom the gai~ ~ correction circuit 204 with the : ~
plurality of-off3et :correction factors stored in the memory 213 of the: off~et unit 214 . The off~et unit : ~ :30 ~14 is responsive t o timing and control signal~
received from the control circuit 210 for providing the offset correction factor to b~ added to the portion of the image signal associated with its re~pective charg~ coupled device.
Accordingly, the circuit described above provides apparatus for correcting the gain and JCV J~
PCT/IJS9~/0144 213Q~3~
IPEA/US 2 2 ~P~ ~994 off ~et of the signal received from each charge coupled device as the signal is provided by the camera 102. It will be apparent to 'those skilled in the art that the gain correction factor~
and the offset correction factors stored in the gain memory 205 of the gain unit 206 and the offset memory 213 of the offset unit 214, respe~ti~ely, can ~:
be determined in a variety of way~. In a presently preferred embodiment o~ the in~ention, calibration slides 104 (Figure 1) are provided 80 that the gain ':
correction factors~and offset correction factors can :~
., be determined~and stored in the gain memory 2Q5 of the gain un:it~206 and the offset memory 213 of the offset unit:214,~ :respectively. However, those -15 ~ sk1lled in the:art~wili appreciate that many other methods and~ apparatus may be~provided for deter~ining the offset~ correction factors and the ain~correction:factors. ; .
Further,~it~will be apparent to~those ~killed 20~ in~;the~art that since the gain and offset correction are~.performed ~on ~analog signal~,; prior ~o the con~ersion by~:the~analog-to-digital converter 222, the~dynamic range of the analog-to-digital converter 222~ need~not~be~sacrificed. A~ an example, if the 25~ -;correction were performed after the~conversion, then a~ p~rtion~ of :~ the dynamic ~range~: of the ~na}og-to-d ~ital converter 222 would~be~unused for signa1~1evels~that~were ;lower than:the~peak: si~nal level~; :Accordingly,~ this~portion of:the~ range of 30~ t~he: converter~ i8 essentially 109t~ t o~ the image : ,:
::: ' : i signal~. ~
: Still ~urther, the subiect invention provides apparatu~ for ~arying the off8et in response to -:variation in~the~intensity of light~provided by the strobe light 114. The photodatector sensor 116 : provides the light signal to an integrator 218 for , A,'-~Ei~,u.3 ~HcEr 3 3 7PC~1! 9 3 / O 1 4 4 2 APR ~9~4 determining the total energy detected by the photodetector sensor 116. The integrator 218 i~
sampled ~y a sample and hold circuit 220, the output .
:: :
:
' ;ci~D SWEEr W093/165Sl PCT/US93/~2 ~ ~-3~3~ o -of which is indicative of-the energy provided by the strobe light 114 and, is therefore indicative of the energy provided to the slide 104. The offset unit 214 is responsive to the signal provided by the sample and hold circuit 220 for varying the individual offset correction factors. To this end, the reference input of the digital-to-analog converter of the offset unit 214 is coupled to receive the signal from the sample and hold circuit ~ 220 so that variation in the intensity of light provided by the~ strobe light 114 will result in : varying the reference for determining the conversion of the proper digltal quantity to the analog signal.
This allows for variation in the offset as a function of the strobe intensity so that the offset may be selected ~to cover any range without sacrificing the dynamic range of the analog to digital circuit 222.
In simi}ar ~ashion, an analog-to-digital ~':20: ~ circuit 222 includes: a referenr input coupled to receive the light:signal from the sample and hold circuit 220~. The analog-to-digital circuit 222 is aonstructed for~ converting the analog image signal recei~ed from th~ offset correc~ion circuit 212 into ~: 2S~ a~plurality of digital signals wherein the plurality of digital signals~represent the image of the slide ~ 4:. since' the: reference input of the - anal-og-to-digital circuit 222 receivss the light ~ signal from the sample and hold circuit 220, the dynamic range of the analog-to-digital convertor 222 is modulated in proportion to the intensity of light provided by t~e strobe light 114 so that variations ~n the intensity of light provided by the strobe light will not affe t the image signals, and so that the image signal is a direct measure of the transmissivity of the specimen, independent of the "
: .
~WQ93/16~51 PCT/US~3/01442 213 ~ 3 3 ~
.
intensity of light provided by the strobe light 114.
It will be apparent to those skilled in the art that although only several presently preferred embodiments of the invention have been described in detail herein, many modifications and variations may be provided without~ departing from the true scope' and spirit of the invention. Accordingly, the invention is not limited except as by the appended clalms.
What is claimed is:
:
: :: ~ : : :
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',:
Description NETHOD ~D ~PP~RATUS FOR DYNAMIC CO~REC~ION
OF MIC~08COPIC T~
:' Technical Field The present invention is directed toward - apparatus for providing signals representing an : lO image of an object and, more particularly, toward method and apparatus for dynamically correcting I
image signals for variations in the illumination of the image or the detection of the image by the camera.
; lSBack~round of the Invention Systems for providing image signals typically ' include a camera positioned to be focused upon an object and con~tructed for providing image signals representing an~image of the object. Typically, 20 ~ ~ these syst~ms include cameras having an array of discrete charge coupled devices ("CCD "), referred o as pixels, for providing electrical signals wherein the magnitude of the electrical signal is indicative~of the intensity of light in ident upon 25~ each pixelO ~By properly timing the man~er that the plurality of~:signals are obtained from the camera, the plurality~of signals can be:used to represent an image of an object upon which the camera is focused.
However,~several factors contribute to fixed ~pattern variations of the plurality of discrete ;~pixel elem2nts imaged by the camera. One factor, referred to: herein as illumination variation, results from nonuniformity in illlt~in~tion caused by ~:: optical element imperfections, dust collection r and 35- positioning variations. Another factor, referred to herein as CCD variation, results from two types of imperfections in the performance of the CCDs. One ~ :performance imperfection results from size tolerance :
W093/165~1 PCT/USg3/01~4~2 ~303~ - 2 -variations on the active area sensitive to light for each pixel. These size imperfections result in sensitivity variations between pixels on a given sensor that are mathematically eguivalent to illumination variation. Illumination ~ariation, whether caused by nonuniformity in illumination or by CÇD size variations are corrected for using gain correction.
Another factor that contributes to fixed pattern variations is also caused by CCD performance imperfections. This factor is referred to as offset variation and is caused by the dark current signal within the CCD, i.e., the current signal that is present at the CCD when no light is incident on the CCD. The offset variation is determined as the magnitude of the signal from a pixel when no light is inc:ident upon the pixel. Illumination variation and offset variation present ~hemselves as two types of errors in~the resulting signal from each pixel.
20 ~ It is~dasirable, therefore, to provide method and~ apparatus for correcting image~ signals from a camera for i~ rin~tion variation, resulting from nonuni~ormity in illumination and from CCD size variation.~ It~is~ also desirable to provide method 25~ and ~pparatus for~ correcting image signals from a camera for offset variation resulting from CCD dark current Further, in order to obtain a plurality of signals from the array of pixel elements that most ~ accurately represent an image of the object, it is : ' :
~' necessary to correct each pixel for the above mentioned variations in offset and illumination.
~ost prior art systems for collecting image signals have attempted to provide data processing methods for correcting the plurality of signals. However, these methods cannot be performed at the same speed W093/165S1 213 ~ 3 ~ 7 PCT/US93/01442 that the si~nals are obtained from the camera and, therefore, introduce significant delay in the time required to obtain an image signal. Further, these methods are also not accurate. Accordingly, it is ~: 5 desirable to provide method and apparatus for ;: correcting a plurality of signals from a CCD camera wherein the correction can be made rapidly while the plurality of signals are obtained from the camera and wherein the correction is made prior to the lo analog-to-digital conversion, to utilize the maximum number of quantization steps to measure signal levels. - .-Summary of the Invention The:present invention comprises a circuit for 15:~ ~ real time corr~ction of an image signal provided by a~camera wherein the image signal represents the image~ of an~ object. The camera: may include a plurality of charge coupled devices for providing a respective~ plurality of pixel signals wherein the ~ plurality of:pixel signals combine to provide the image signal. ~The circuit of the subject invention nGludes memory ~or storing ~a plurality of ~ correction factors wherein each~of:the plurality of C~ corre tion:factors is associated:~with a:~respective 25~ one of the plurality of charge coupled devices. The oircuit also ~includes signal processing ~eAn~ for combining ~each of~ the plurality; of ~correction factors with the respective one of the plurality of ,~,, ~ , pixel signals with which it is associated. In a 30~ first presently preferred embodiment of the ~ ~: ; : invention, the correction factors are related to the incident, ' unmodulated light and gain of the individual charge coupled devices and the signal processing circuit is a circuit: constructed to multiply the correction factors by the plurality of pixel signals. In a second presently pr~ferred 2~3033~ ..
embodiment of the invention, the correction factors are offset correction factors associated w~th the of~sets of the plurality of charge coupled devices and the signal processing circuit is an adder for adding the plurality for offset correction- factors to the plurality of pixel signals.
In still another embodiment of the invention, . :
the apparatus includes a light assembly for providing light to illuminate the object and for ~ providing a light signal 1ndicative of the intensity of the light.~ The signal processing circuit is further responsive to the light signal for altering the reference~and offset factors so that the image signal is corrected for variations in the intensity 15~ of~the light~
Brief Descri~t~ion of the Drawings Figure I is an ilIustrative diagram of a camera~ system~ constructed in accordance with the pre~sent invention; and ~ ~
20~ . Figure ~2 is a more detailed illustrative diagram~of~the~daea~processor illustrated in Figure Detailed~Description of the Invention ~
e~ subject invention-~provides~ method and 25~ appa}atus for dynamically correcting ~image signals from a camera for~fixed pattern variation in gain, illumination, ~and offset. A camera systém lO0 is illustrated~ in ~Figure l. The camera system lO0 includes a CCD camera 102~ for providing an image ~ signal representing the image of an object. As an example, the camera system lO0 may be a camera system for obtAin;ng and analyzing medical specimens. However, those skilled in the art Will appreciate~that the subject invention is applicable 35 ~ to camera systems 100 constructed for obtaining the - image signal of a wide variety of transmissive : ~ :
~,WO93~16551 2 1 3 ~ 3 3 ~ PCT/US93/01442 objects.
~; The slide 10~ is mounted to a motion ~ controller-106;that provides a scan signal to a data ',~ - processor 108 to indicate that the slide 104 is ~'5 ~ being moved into position for an image to be ; obtained. ~ The motion controller 106 may comprise any of a~ variety of suitable devices readily available to those~skilled in the art.
An illuminat~ion system 112 includes a strobe 10~ ~ light 114, ~a~photodetector sensor 116, and a beam splitter~118. ~The illumination system 112 may also include collector~and~projection optics 113, a lens and~aperture 115, and a condenser lens and aperture 117,~disc~lese~in more;detail below. ~The strobe 15~ 1ight ~114 is~responsive to a~flash signal received Pr;om~the data~proceccor 108 for providing~a flash of light.~The~ L ~ light 114 is also~responsive to "~ an~intensi ~ signal~for varying the~intensity of the flash~of light~provided. The data~procec~or 108 is 2;0~ O~ngive~to~the,~,scan signal for~synchronizing the oaméra~,~102~and ,the~ LIobe~;light~114~to~ gather the ,image~ Suitable,~strobe lights~ ll4 for~ operation the'~ subject~invention~as~dèscribed~,herein may r~ l'y~sel'e~ted~by:those::skilI;ed~:~in:the art from 25~ a~- variety~of~strobe~ lights~that-~are commercially avai~lable.~ r~hèr,~ it will~be~apparent to those skilled~ in~,~the art ~that, although ~'the present invention :iS described-by reference to a strobe light 114,~for~provlding a flash of light, other 30~ devices~ constructed to provide ~a continuous source ~ of light ~may~bé readily~ substitu~ted there for n,~ 'without departing from the true s~cope and spirit of the subject~invention.
The~phot d etector sensor ll6 is constructed ;35~ to receive~a;portion of the flash of light from the stro~e light~ll4~via a beam splitter 11~. The beam ~,, :
WOg3/165~1 PCT/US93/01442 2~ 3~ - 6 -splitter 118 may comprise any of a variety of devices co~r~rcially available for splitting a beam of light into component parts. The photodetector sensor 116 is constructed to provide a light signal indicative of the intensity of light provided by the strobe light 114. The light signal is coupled to the data processor 108 and is used for correcting the image signal received from the camera 102, as will be described in more detail below.
.
lo The collector and projection optics 113, the lens and aperture 115, and the condenser lens and aperture ~I17 are each provided for optically tr~n~m;tting the flash of light from the strobe light 114 to the photodetector sensor 116 and the ; I5 slide 104. Standard elements appropriate for optically transmitting the flash of light are commercially available and may be readily selected by those skilled in the art~ Additionally, it will ;be~ apparent~ to those skilled~ in the art that ';20~ alternative arrangements for optically transmitting the flash of light from the strobe light 114 to the photodetector sensor 116 and the slide 104 may be provided without departing from the~scope and spirit of the subject invention. ~ ~
25 ~ The càmera 102 may comprise a video camera ncluding a~plurality of charge coupled devices for ;providing ~a plurality of signals wherein the plùrality of signals may ~e combined to provide the ' ' image signal to the data processor 108. As is known in the art,~the plurality of charge coupled devices, also referred to as pixel elements, each provide a signal indicative of the intensity of light incident thereon. However, since the plurality of pixel elements are discrete one from another, they each 3~ have slightly different gain and offset characteristics that introduce minor inaccuracy in ~' :
PCTIUS93/01~ ~2 ~ 13 o 3 3 t,7 lPEA/us 2 2 APR 199 the re~ulting image qignals. Additionaliy the unmodulated illumination incident on the CCD pixel~
is nonuniform and, therefore, further reduces the ~~accuracy of the resulting image ~ignals.
Accordingly, the data processor 108 includ2s circuitry for correcting the plurality of signals received from the pixel elements of~t~e camera lO2 for ~ariation in offqet, gain, and illumination nonuniformity between pixel elements.
10: A suitable correction circuit 200 i~
llu~trated in Figure 2. The circuit 200 includes an amplifier 202 for receiving and amplifying the ~;; image :signal provided.by the camera 102. The :~: : amplifier 202 i9 coupled to a gain correction ~: 15circui~ 204 for correcting the image si~nal for pixel-to-pixel variation in gain and illumination.
The gain correction circuit 204 includes a gain unit 206 coupled to a multip.lication circuit 208 and : re~ponqive to timing and control 8ignal9 received 20: from a control circuit 210 for multiplying the image iy~al by a~plurality of predetermined gain factors.
The gain uni~ 206 co~ Lise a memory unit 205 : coupled:to a digital-to-analog converter 207 for providing analog correction 3ignal to the : 25~mu}tiplication circuit 208. The memory 205 i8 selected ~o 3tore predeter~i~e~ cG~ction factor3.
; ~ ~
The digi~al-to-analog con~er~er 207 i~ ~caled ~o : that it~ ~t~p re~olution i5 les than that of ~he analog-to-digital converter 222. Thi3 allow~ the 30correc~io~ to be placed rea30nably cen~ered within ~: , the analo~-to-digital converter step size and results i~ accurate correction~without sacrificing the dynamic range of the analog-to-digit~l con~erter 222.
35A~ discussed aboYe, the image ~i~nal includes ~:~ a plurality of signals obt~; n~ from an array of ~ r~l~F~sH~ET
~13D~7 Pcr/JS 9 33 / o ~
IPEA/US 2 ? APR 1994 di3crete charge coupled devic~, or pixel elements, of the camera 102. - A~ al90 discu~3ed above, the gain and incident illumination of the pluraIity of ~ charge coupled device~ may vary slightly.
s Accordingly, a plurality of gain corr~ction factorq are stored in the memory 205 of the gain unit 206, each a~sociated with a respective charge coupled de~ice of the camera 102. The control circuit 210 provides timing and control signal~ to the gain unit 206 so that each gain factor i9 multiplied by it~
respective portion of the image qignal in the multiplier 208,;thereby correcting each respective portion of the image signal for any varia~ion in it~
respective charge coupled device or incident illumination and, thereby, substantially eiiminating undesirable effects o~ gain variation or illumination nonllniformity from the re~ulting image ~ignals.
Similarly, an offqet correction circuit 212 :include.c an off et unit 21~ including an offset memory 213: for ~toring a plurality of offset : correction factor~,~ each associated with a :: respecti~re one of the plurality of charge coupled : device3 of the ~amera 102, and a digital-to-analog 25~ co~lvert~r 215. The offset correction circuit 212 includ~s an adder 216 for adding the image signal ; ~ ~rom the gai~ ~ correction circuit 204 with the : ~
plurality of-off3et :correction factors stored in the memory 213 of the: off~et unit 214 . The off~et unit : ~ :30 ~14 is responsive t o timing and control signal~
received from the control circuit 210 for providing the offset correction factor to b~ added to the portion of the image signal associated with its re~pective charg~ coupled device.
Accordingly, the circuit described above provides apparatus for correcting the gain and JCV J~
PCT/IJS9~/0144 213Q~3~
IPEA/US 2 2 ~P~ ~994 off ~et of the signal received from each charge coupled device as the signal is provided by the camera 102. It will be apparent to 'those skilled in the art that the gain correction factor~
and the offset correction factors stored in the gain memory 205 of the gain unit 206 and the offset memory 213 of the offset unit 214, respe~ti~ely, can ~:
be determined in a variety of way~. In a presently preferred embodiment o~ the in~ention, calibration slides 104 (Figure 1) are provided 80 that the gain ':
correction factors~and offset correction factors can :~
., be determined~and stored in the gain memory 2Q5 of the gain un:it~206 and the offset memory 213 of the offset unit:214,~ :respectively. However, those -15 ~ sk1lled in the:art~wili appreciate that many other methods and~ apparatus may be~provided for deter~ining the offset~ correction factors and the ain~correction:factors. ; .
Further,~it~will be apparent to~those ~killed 20~ in~;the~art that since the gain and offset correction are~.performed ~on ~analog signal~,; prior ~o the con~ersion by~:the~analog-to-digital converter 222, the~dynamic range of the analog-to-digital converter 222~ need~not~be~sacrificed. A~ an example, if the 25~ -;correction were performed after the~conversion, then a~ p~rtion~ of :~ the dynamic ~range~: of the ~na}og-to-d ~ital converter 222 would~be~unused for signa1~1evels~that~were ;lower than:the~peak: si~nal level~; :Accordingly,~ this~portion of:the~ range of 30~ t~he: converter~ i8 essentially 109t~ t o~ the image : ,:
::: ' : i signal~. ~
: Still ~urther, the subiect invention provides apparatu~ for ~arying the off8et in response to -:variation in~the~intensity of light~provided by the strobe light 114. The photodatector sensor 116 : provides the light signal to an integrator 218 for , A,'-~Ei~,u.3 ~HcEr 3 3 7PC~1! 9 3 / O 1 4 4 2 APR ~9~4 determining the total energy detected by the photodetector sensor 116. The integrator 218 i~
sampled ~y a sample and hold circuit 220, the output .
:: :
:
' ;ci~D SWEEr W093/165Sl PCT/US93/~2 ~ ~-3~3~ o -of which is indicative of-the energy provided by the strobe light 114 and, is therefore indicative of the energy provided to the slide 104. The offset unit 214 is responsive to the signal provided by the sample and hold circuit 220 for varying the individual offset correction factors. To this end, the reference input of the digital-to-analog converter of the offset unit 214 is coupled to receive the signal from the sample and hold circuit ~ 220 so that variation in the intensity of light provided by the~ strobe light 114 will result in : varying the reference for determining the conversion of the proper digltal quantity to the analog signal.
This allows for variation in the offset as a function of the strobe intensity so that the offset may be selected ~to cover any range without sacrificing the dynamic range of the analog to digital circuit 222.
In simi}ar ~ashion, an analog-to-digital ~':20: ~ circuit 222 includes: a referenr input coupled to receive the light:signal from the sample and hold circuit 220~. The analog-to-digital circuit 222 is aonstructed for~ converting the analog image signal recei~ed from th~ offset correc~ion circuit 212 into ~: 2S~ a~plurality of digital signals wherein the plurality of digital signals~represent the image of the slide ~ 4:. since' the: reference input of the - anal-og-to-digital circuit 222 receivss the light ~ signal from the sample and hold circuit 220, the dynamic range of the analog-to-digital convertor 222 is modulated in proportion to the intensity of light provided by t~e strobe light 114 so that variations ~n the intensity of light provided by the strobe light will not affe t the image signals, and so that the image signal is a direct measure of the transmissivity of the specimen, independent of the "
: .
~WQ93/16~51 PCT/US~3/01442 213 ~ 3 3 ~
.
intensity of light provided by the strobe light 114.
It will be apparent to those skilled in the art that although only several presently preferred embodiments of the invention have been described in detail herein, many modifications and variations may be provided without~ departing from the true scope' and spirit of the invention. Accordingly, the invention is not limited except as by the appended clalms.
What is claimed is:
:
: :: ~ : : :
- ~ :
~ . , .:.: .:
::
::
:' ~ ~ , ' ~
',:
Claims (23)
1. Apparatus for dynamically correcting an image signal comprising:
camera (102) means for providing an image signal, wherein the image signal represents a transmissivity of an object;
light means (112) for providing light to illuminate the object and for providing a light signal indicative of the intensity of said light;
and data processing means (108) responsive to said light signal for dynamically correcting said image signal so that said image signal is corrected for variations in the intensity of said light.
camera (102) means for providing an image signal, wherein the image signal represents a transmissivity of an object;
light means (112) for providing light to illuminate the object and for providing a light signal indicative of the intensity of said light;
and data processing means (108) responsive to said light signal for dynamically correcting said image signal so that said image signal is corrected for variations in the intensity of said light.
2. The apparatus as recited in claim 1 wherein said data processing means (108) comprises an analog-to-digital converter (222) having an analog input for receiving the image signals and a reference input for receiving said light signal, said analog-to-digital converter (222) having an output providing the corrected image signals.
3. The apparatus as recited in claim 1 wherein the camera (102) includes a plurality of charge coupled devices (102) for providing a respective plurality of pixel signals and wherein the plurality of pixel signals combine to provide the image signal, said data processing means (108) comprising:
offset correction means (212) for storing a plurality of offset correction factors, each associated with a respective one of said plurality of charge coupled devices (102), said offset correction means (212) being further constructed to combine said plurality of offset correction factors with the respective ones of the plurality of pixel signals to thereby correct the image signal for variation in offsets between the plurality of charge coupled devices (102).
offset correction means (212) for storing a plurality of offset correction factors, each associated with a respective one of said plurality of charge coupled devices (102), said offset correction means (212) being further constructed to combine said plurality of offset correction factors with the respective ones of the plurality of pixel signals to thereby correct the image signal for variation in offsets between the plurality of charge coupled devices (102).
4. The apparatus as recited in claim 3 wherein said offset correction means (212) further comprises means responsive to variations in the intensity of said light signal for varying the value of said plurality of offset correction factors as the image signal is provided by the camera.
5. The apparatus as recited in claim 3 wherein said offset correction means (212) further comprises:
memory means (213) for storing said plurality of offset correction factors; and a digital-to-analog converter (215) having a digital input for receiving the plurality of offset correction factor and a reference input for receiving said light signal, said digital-to-analog converter (215) having an output providing the plurality of offset correction factors in response to the light signal.
memory means (213) for storing said plurality of offset correction factors; and a digital-to-analog converter (215) having a digital input for receiving the plurality of offset correction factor and a reference input for receiving said light signal, said digital-to-analog converter (215) having an output providing the plurality of offset correction factors in response to the light signal.
6. The apparatus as recited in claim 1 wherein the camera (102) include a plurality of charge coupled devices (102) for providing a respective plurality of pixel signals wherein the plurality of pixel signals combine to provide the image signal, said data processing means (108) comprises:
gain correction means (204) for storing a plurality of gain factors, each associated with a respective one of said plurality of charge coupled devices (102), said gain correction means (204) being further constructed to multiply (208) said plurality of gain factors by the respective ones of the plurality of pixel signals to thereby correct the image signal for variation in the sensitivity and incident illumination (112) of the plurality of charge coupled devices (102).
gain correction means (204) for storing a plurality of gain factors, each associated with a respective one of said plurality of charge coupled devices (102), said gain correction means (204) being further constructed to multiply (208) said plurality of gain factors by the respective ones of the plurality of pixel signals to thereby correct the image signal for variation in the sensitivity and incident illumination (112) of the plurality of charge coupled devices (102).
7. The apparatus as recited in claim 6, further comprising:
offset correction means (212) for storing a plurality of off et correction factors, each associated with a respective one of said plurality of charge coupled devices (102), said offset correction means (212) being further constructed to add said plurality of offset correction factors to the respective ones of the plurality of pixel signals to thereby correct the image signal for variation in offsets between the plurality of charge coupled devices (102).
offset correction means (212) for storing a plurality of off et correction factors, each associated with a respective one of said plurality of charge coupled devices (102), said offset correction means (212) being further constructed to add said plurality of offset correction factors to the respective ones of the plurality of pixel signals to thereby correct the image signal for variation in offsets between the plurality of charge coupled devices (102).
8. The apparatus as recited in claim 7 wherein said offset correction means (212) further comprises means responsive to the variations in the intensity of said light signal for varying the value of said plurality of offset correction factors as the image signal is provided by the camera.
9. The apparatus as recited in claim 7 wherein said offset correction means (212) further comprises:
memory means (213) for storing said plurality of offset correction factors; and a digital-to-analog converter (215) having a digital input for receiving the plurality of offset correction factors and a reference input for receiving said light signal, said digital-to-analog converter (215) having an output which provides the plurality of offset correction factors in response to the light signal.
memory means (213) for storing said plurality of offset correction factors; and a digital-to-analog converter (215) having a digital input for receiving the plurality of offset correction factors and a reference input for receiving said light signal, said digital-to-analog converter (215) having an output which provides the plurality of offset correction factors in response to the light signal.
10. A circuit for correcting an image signal comprising:
camera (102) means for providing an image signal, wherein the image signal represents a transmissivity of an object and wherein the camera (102) includes a plurality of charge coupled devices (102) for providing a respective plurality of pixel signals wherein the plurality of pixel signals combine to provide the image signal;
memory means (213) for storing a plurality of correction factors wherein each of said plurality of correction factors is associated with a respective one of the plurality of charge coupled devices (102); and signal processing means (200) for combining each of said plurality of correction factors with the respective one of the plurality of pixel signals with which it is associated.
camera (102) means for providing an image signal, wherein the image signal represents a transmissivity of an object and wherein the camera (102) includes a plurality of charge coupled devices (102) for providing a respective plurality of pixel signals wherein the plurality of pixel signals combine to provide the image signal;
memory means (213) for storing a plurality of correction factors wherein each of said plurality of correction factors is associated with a respective one of the plurality of charge coupled devices (102); and signal processing means (200) for combining each of said plurality of correction factors with the respective one of the plurality of pixel signals with which it is associated.
11. The circuit as recited in claim 10 wherein said signal processing means (200) further comprises means (216) for adding said plurality of correction factors to the respective ones of the plurality of pixel signals.
12. The circuit as recited in claim 10 wherein said signal processing means (200) further comprises means (208) for multiplying said plurality of correction factors to the respective ones of the plurality of pixel signals.
13. The circuit as recited in claim 10 wherein said memory means (205) comprises means for storing a plurality of gain correction factors each associated with a respective one of the plurality of charge coupled devices (102) and a plurality offset correction factors each associated with a respective one of the plurality of charge coupled devices (102).
14. The circuit as recited in claim 13 wherein said signal processing means (200) comprises:
an adder (216) for adding said plurality of offset correction factors to the respective ones of the plurality of pixel signals; and a multiplier (208) for multiplying the plurality of gain correction factors to the respective ones of the plurality of pixel signals.
an adder (216) for adding said plurality of offset correction factors to the respective ones of the plurality of pixel signals; and a multiplier (208) for multiplying the plurality of gain correction factors to the respective ones of the plurality of pixel signals.
15. The circuit as recited in claim 10, further comprising:
light means (112) for providing light to illuminate the object and for providing a light signal indicative of the intensity of said light, said signal processing means (200) being responsive to said light signal for altering said plurality of correction factors.
light means (112) for providing light to illuminate the object and for providing a light signal indicative of the intensity of said light, said signal processing means (200) being responsive to said light signal for altering said plurality of correction factors.
16. An apparatus for dynamically correcting an image signal provided by a camera (102) wherein the image signal represents a transmissivity of an object, said apparatus comprising:
light means (112) for providing light to illuminate the object and for providing a light signal indicative of the intensity of said light;
and data processing means (108) responsive to said light signal for dynamically correcting said image signal so that said image signal is corrected for variations in the intensity of said light wherein said data processing means (108) comprises an analog-to-digital converter (222) having an analog input for receiving the image signals and a reference input for receiving said light signal, said analog-to-digital converter (222) having an output providing the corrected image signals.
light means (112) for providing light to illuminate the object and for providing a light signal indicative of the intensity of said light;
and data processing means (108) responsive to said light signal for dynamically correcting said image signal so that said image signal is corrected for variations in the intensity of said light wherein said data processing means (108) comprises an analog-to-digital converter (222) having an analog input for receiving the image signals and a reference input for receiving said light signal, said analog-to-digital converter (222) having an output providing the corrected image signals.
17. The apparatus as recited in claim 16 wherein the camera (102) includes a plurality of charge coupled devices (102) for providing a respective plurality of pixel signals and wherein the plurality of pixel signals combine to provide the image signal, said data processing means (108) comprising an offset correction means (212) for storing a plurality of offset correction factors, each associated with a respective one of said plurality of charge coupled devices (102), said offset correction means (212) being further constructed to combine said plurality of offset correction factors with the respective ones of the plurality of pixel signals to thereby correct the image signal for variation in offsets between the plurality of charge coupled device (102).
18 The apparatus as recited in claim 17 wherein said offset correction means (212) further comprises means responsive to variations in the intensity of said light signal for varying the value of said plurality of offset correction factors as the image signal is provided by the camera (102).
19. The apparatus as recited in claim 17 wherein said offset correction means (212) further comprises:
memory means (213) for storing said plurality of offset correction factors; and a digital-to-analog converter (215) having a digital input for receiving the plurality of offset correction factors and a reference input for receiving said light signal, said digital-to-analog converter (215) having an output providing the plurality of offset correction factors in response to the light signal.
memory means (213) for storing said plurality of offset correction factors; and a digital-to-analog converter (215) having a digital input for receiving the plurality of offset correction factors and a reference input for receiving said light signal, said digital-to-analog converter (215) having an output providing the plurality of offset correction factors in response to the light signal.
20. The apparatus as recited in claim 16 wherein the camera (102) includes a plurality of charge coupled devices (102) for providing a respective plurality of pixel: signals wherein the plurality of pixel signals combine to provide the image signal and said data processing means (108) comprises a gain correction means (204) for storing (205) a plurality of gain factors, each associated with a respective one of said plurality of charge coupled devices (102), said gain correction means (204) being further constructed to multiply said plurality of gain factors by the respective ones of the plurality of pixel signals to thereby correct the image signal for variations in the sensitivity and incident illumination (112) of the plurality of charge coupled devices (102).
21. The apparatus as recited in claim 20, further comprising offset correction means (212) for storing a plurality of offset correction factors, each associated with a respective one of said plurality of charge coupled devices (102), said offset correction means (212) being further constructed to add said plurality of offset correction factors to the respective ones of the plurality of pixel signals to thereby correct the image signal for variation in offsets between the plurality of charge coupled devices (102).
22. The apparatus as recited in claim 21 wherein said offset correction means (212) further comprises means responsive to the variations in the intensity of said light signal for varying the value of said plurality of offset correction factors: as the image signal is provided by the camera (102).
23. The apparatus as recited in claim 21 wherein said offset correction means (212) further comprises:
memory means (213) for storing said plurality of offset correction factors; and a digital-to-analog converter (215) having a digital input for receiving the plurality: of offset correction factors and a reference input for receiving said light signal, said digital-to-analog converter (215) having an output which provides the plurality of offset correction factors in response to the light signal.
memory means (213) for storing said plurality of offset correction factors; and a digital-to-analog converter (215) having a digital input for receiving the plurality: of offset correction factors and a reference input for receiving said light signal, said digital-to-analog converter (215) having an output which provides the plurality of offset correction factors in response to the light signal.
Applications Claiming Priority (2)
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|---|---|---|---|
| US07/838,065 US5361140A (en) | 1992-02-18 | 1992-02-18 | Method and apparatus for dynamic correction of microscopic image signals |
| US07/838,065 | 1992-02-18 |
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| US5361140A (en) | 1994-11-01 |
| EP0627151A4 (en) | 1995-02-01 |
| WO1993016551A1 (en) | 1993-08-19 |
| AU3723393A (en) | 1993-09-03 |
| JPH07504303A (en) | 1995-05-11 |
| JP2954704B2 (en) | 1999-09-27 |
| CA2130337A1 (en) | 1993-08-19 |
| EP0627151A1 (en) | 1994-12-07 |
| AU670265B2 (en) | 1996-07-11 |
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