WO1993016439A1

WO1993016439A1 - Method and apparatus for rapid capture of focused microscopic images

Info

Publication number: WO1993016439A1
Application number: PCT/US1993/001449
Authority: WO
Inventors: Jon Wallace Hayenga; Louis R. Piloco
Original assignee: Neopath, Inc.
Priority date: 1992-02-18
Filing date: 1993-02-18
Publication date: 1993-08-19
Also published as: AU3723993A

Abstract

A camera (102) system is provided for providing image signals representing the image of an object. The camera (102) system includes a strobe assembly (114) and a data processor (108) controlled motion controller (106) for synchronizing the capture of image signals with a flash of light thereby to substantially eliminate variation in the image signal due to vibration in the object or the camera (102). The camera (102) system further includes a camera assembly (102) for providing a focus plus and a focus minus signal (316, 318) wherein the data processor (108) is responsive to the band-pass frequency energy (504) component of the focus plus and focus minus signal to determine the proper positioning of the object so that the image provided by the camera (102) will be representative of a focused image. A correction unit (502) is provided for enabling pixel-to-pixel correction of the camera (102)

Description

METHOD AND APPARATUS FOR RAPID CAPTURE OF FOCUSED MICROSCOPIC IMAGES Technical Field

The present invention is directed toward devices for providing image signals representing an image of an object and, more particularly, apparatus for rapidly capturing focused image signals. Background of the Invention

Systems for providing image signals typically include a camera positioned to be focused upon an object and constructed for providing image signals representing an image of the object. Typically, these systems include apparatus for monitoring the image signals and for varying the focus of the camera to provide a focused image signal. However, in such systems, it is not possible to obtain a focused image if any significant relative motion exists between the image and the camera while the image is being obtained.

To eliminate the effect of relative vibration between the camera and the object prior art systems typically require a waiting period, or settling time, for all relative motion between the camera and the object to stop before the image is obtained. For this reason, the time required to obtain the image signals using these camera systems is undesirably long. Accordingly, it is desirable to provide a camera system capable of obtaining image signals wherein the camera system is capable of operation during times when the object or camera vibrates.

Further, even when the object or the camera is not vibrating, the above-referenced camera systems require an unacceptably long time to focus the camera. This is because the above-described focusing mechanism requires a focused signal to be received before the proper focusing position of the camera can be determined. Accordingly, the focus of the camera must be varied until an acceptably focused image signal is received, before the desired image signal can be obtained. This procedure is unacceptable and tedious. The focus time of these systems is further increased since changing the focus causes vibration that must be stopped before the desired image signals can be obtained. It is desirable, therefore, to provide a camera system capable of determining the proper focus position of the camera without the necessity of receiving focused image signals.

Several prior art systems have attempted to reduce the time required to focus a camera by obtaining a preliminary image, where the focus of the preliminary image. These systems then use data processing methods to determine whether the preliminary image was in focus and, if not, to determine the proper focus of the image. However, such systems still require a settling time before the preliminary image can be obtained. Further, these systems require that the entire image be obtained before a determination of focus can be made. Also, if the preliminary image is determined to be out of focus, the entire process must be repeated, before the camera is moved, to obtain the in-focus image.

Still further, obtaining image signals representing a plurality of objects with the above-referenced camera system is time-consuming because each object must be focused and focused image signals provided before an image of the next object can be taken. The time wasted focusing upon a single object and waiting for vibration to stop is multiplied by the number of objects for which image signals are desired. Therefore, these systems become even more unacceptable as the number of objects increases. Accordingly, it is desirable to provide a camera system wherein a large number of image signals can be obtained rapidly. Summary of the Invention

In one preferred embodiment of the invention, a camera system is provided for obtaining a signal representing a focused image of an object. The camera system includes a camera assembly responsive to a focus signal for focusing on a focal point to provide an image signal indicative of the image of the object*. The camera assembly is also constructed to provide an offset focus signal focusing the camera assembly on an offset focal point displaced from the focal point by a predetermined distance. The camera system further includes a focus signal processor for determining the band-pass frequency component of the offset focus signal to provide the focus signal so that the image signal provided by the camera assembly will be representative of a focused image of the object. In another presently preferred embodiment of the invention, a light assembly is constructed for providing light to illuminate the object and to provide a light signal indicative of the intensity of the light provided. The camera system also includes a camera assembly for providing an image signal indicative of the image of the object. The camera system also includes a data processor responsive to the light signal for altering the image signal so that the image signal is corrected for variations in intensity of the flash of light. Brief Description of the Drawings

Figure 1 is an illustrative block diagram of the camera system that is the subject of the present invention; Figure 2 is a graph illustrating the relationship between the passband frequency component of the signal provided by the camera assembly of Figure 2 and the focus of the camera assembly; Figure 3 is a more detailed illustrative diagram of the camera assembly that comprises the subject invention;

Figure 4 is an illustrative diagram of a circuit for determining the focus position of the camera assembly of Figure 3; and

Figure 5 is an illustrative block diagram of a circuit for controlling the camera assembly of

Figure 3.

Detailed Description of the Invention The subject invention provides a camera system for rapidly obtaining focused images of an object. The camera system of the subject invention may be used in various imaging devices as will be apparent to those skilled in the art. In a presently preferred embodiment of the invention, the camera system disclosed herein is used in a system for analyzing cervical pap smears.

A camera system 100 constructed in accordance with the subject invention is illustrated in Figure 1. Therein, a camera assembly 102 is positioned to obtain an image of a slide 104 mounted to a motion controller 106. In a presently preferred embodiment of the invention, the slide 104 is constructed for receiving a slide-mounted medical specimen and the camera system 100 is provided for obtaining image signals of the medical specimen. However, as will be apparent to those skilled in the art upon a reading of the following detailed description of the invention, the subject invention may be used with camera systems constructed for obtaining image signals of a wide variety of objects.

The motion controller 106 includes a stage for receiving the slide 104 and is responsive to a slide scan signal, received from a data processor 108, for moving the stage in a slide plane represented by X and Y directions. In the illustrative diagram of Figure 1, the X and Y directions are located in the plane that is perpendicular t * in optical path 110 intermediate the slide 104 and the camera 102. The motion controller is further responsive to a slide focus signal for moving the stage in a direction normal to the slide plane, along the optical path 110, for focusing the camera upon the slide 104. The motion controller is constructed to provide a position signal to the data processor 108 wherein the position signal is indicative of the X, Y, and Z position of the stage. Motion controllers for performing the above-described functions are known in the art and a suitable motion controller may be selected by those skilled in the art.

The camera assembly 102 is constructed to provide an image signal indicative of the optical trans issivity of the specimen on the slide 104. The image signal from the camera assembly 102 is obtained by focusing the camera assembly on a focal point positioned a first distance along the optical path 110. The camera assembly 102 is further constructed to provide an above focus image signal and a below focus image signal, referred to herein as a focus plus and a focus minus signal, respectively. The focus plus signal is provided by focusing the camera assembly on a focal point positioned a second distance along the optical path 110 wherein the length of the second distance is greater than the length of the first distance. The focus minus signal is provided by focusing the camera assembly on a focal point positioned a third distance along the optical path 110 wherein the length of the third distance is less than the length of the first distance. The image signal, focus plus signal, and focus minus signal are each provided to the data processor 108.

The data processor 108 uses the focus plus signal and the focus minus signal to determine the positioning of the slide 104 along the optical path 110 necessary for focusing the specimen so that the image signal provided by the camera 102 will be in focus. More particularly, the data processor 108 determines whether the received signal is of magnitude large enough to focus, whether the image plane lies within the correctable region, and which direction to move the slide 104 to focus the image.

Generally, the data processor 108 determines the magnitude of the band-pass frequency energy in the focus plus and focus minus signals. As illustrated in Figure 2, the image signal will be in focus when the band-pass frequency energy of the focus plus and focus minus signals are substantially equal. Accordingly, to determine the proper positioning of the slide 104 along the optical path 110, the data processor 108 need only determine how far the slide must be displaced for the energy provided by the focus plus and focus minus signals to be substantially equal. It will be apparent to those skilled in the art that the relative positioning of the focal point of the camera assembly when providing the focus plus signal and focus minus signal is determinative of the relationship between their band-pass frequency energy components and the positioning of the camera assembly for providing a focused image signal. So that the image signals may be obtained more rapidly, the data processor 108 is constructed to provide the scan signal to position the motion controller 106 in a plurality of X-Y positions to obtain a plurality of image signals indicative of a respective plurality of images of a portion of the specimen on the slide 104. The data processor 108 may be further constructed to determine the proper positioning of the slirle 104 along the optical path 110 for each of the plurality of image signals obtained. After ear . of the plurality of image signals have been obtained, the data processor 108 can determine whether the slide is focused by examining the band-pass frequency component of the focus plus signal and the focus minus signal, as discussed above. If the image signals were not focused, the data processor 108 will determine the proper positioning of the slide for focus and will provide the scan signal to the motion controller 106 to reposition the slide 104 in the X-Y positions of the portions not focused and, simultaneously, provide the slide focus signal to the motion controller 106 to obtain the proper positioning of the slide 104 along the optical path 110 so that focused image signals are obtained. A strobe assembly 112 is provided for selectively illuminating the slide 104 at the time that the image signals are obtained by the camera 102. The strobe assembly 112 includes a strobe light 114 that is responsive to a pulse signal from the data processor 108 for providing a flash of light. The strobe light 114 is further responsive to an intensity signal received from the data processor 108 for varying the intensity of the flash of light provided. The strobe light 114 is positioned to illuminate the slide 104 with the flash of light. In the illustrative diagram of Figure 1, the slide 104 is positioned intermediate the strobe light 114 and the camera 102 so that the flash of light is provided along an optical path the same as the optical path 110. The strobe assembly 112 further includes a photodetector sensor 116 that is positioned to receive a portion of the flash of light via a beam splitter 118. • ≥ beam splitter 118 may comprise any of a variety of devices readily available to those skilled in the art. The photodetector sensor 116 is^" responsive to the portion of the flash of light to provide a light signal indicative of the intensity of the portion of the flash of light received. Suitable photodetector sensors 116 are readily available commercially.

The data processor 108 is responsive to the light signal received from the photodetector sensor 116 for altering the image signal to compensate the image signal for variations in the intensity of the flash of light provided by the strobe 114. In accordance with a particular feature of the present invention, the data processor 108 provides the scan signal to the motion controller 106 so that a plurality of image signals may be obtained without waiting for vibration in the motion controller 106 or camera 102 to stop. Since the flash of light provided by the strobe assembly only illuminates the specimen for an instant, the motion of the motion controller 106 is substantially frozen and, therefore, will not have any substantial effect on the focus of the image signal provided by the camera assembly 102.

Further, as will be discussed below, the data processor 108 is capable of controlling the camera system 100 so that image sicrrtals may be obtained immediately after the mot..on controller 106 positions the slide 104 in response to the scan signal from the data processor. After the motion controller 106 has moved the slide into position, the motion controller stops moving, leaving only residual vibration. It is noted that the vibration of the motion controller 106 exhibits a predetermined profile, i.e., it vibrates with substantially the same profile after each stop. As discussed herein, the data processor 108 is capable of determining the exact displacement necessary to bring an image into focus. This displacement is determined notwithstanding the vibration of the motion controller 106. Essentially, the data processor 108 obtains the image signal a predetermined amount of time after the motion controller 106 moves the slide into position and relies upon the motion controller 106 exhibiting the same vibration profile so that, any vibration that existed at the time the displacement for focus was determined will be substantially the same as the vibration error present when the motion controller returned to obtain the proper image signal and, accordingly, the focus determination will not be affected. A more detailed diagram of the camera assembly 102 is provided in the illustrative diagram of Figure 3. Therein, an optical transmission assembly 300 includes an objective lens assembly 302, a first beam splitter 304 and a second beam splitter 306. The first and second beam splitters 304 and 306 provide first, second, and third optical paths 308, 310, and 312, respectively. The objective lens assembly 302 is constructed to vary the magnification provided to the specimen on the slide 104. In a presently preferred embodiment of the invention, the objective lens assembly 302 is responsive to a magnification signal received from the data processor 108 to select various lenses to vary the magnification. Suitable assemblies for responding to an electric signal to move two or more lenses into and out of position for varying the magnification provided to the specimen may readily be provided by those skilled in the art.

A primary camera 314 is positioned to receive a first image of the specimen on the slide 104 via the first optical path 308. The first optical path 308 is the path from point A on the objective 302 to point B at the CCD of the primary camera 314. The primary camera 314 is responsive to an activation signal for providing an image signal representing the first image. A focus plus camera 316 is positioned to receive a second image of the specimen on the slide 104 along a second optical path 310. The second optical path 310 is the path from point A on the objective 302 to point C at the CCD of the focus plus camera 316. As discussed above by reference to Figures 1 and 2, the length of the second optical path 310 is less than the length of the first optical path by a predetermined length. The focus plus camera 316 is also responsive to the activation signal for providing a focus plus signal, wherein the focus plus signal is indicative of the focus of the image signal. A focus minus camera 318 is positioned to receive a third image of the object on the slide 104 via a third optical path 312. The third optical path is the path from point A on the objective 302 to a point D on the CCD of the focus minus camera 318. The length of the third optical path 312 is greater than the length of the first optical path 308 by the predetermined length. The focus minus camera 318 is responsive to the activation signal for providing a focus minus signal that is also indicative of the focus of the image signal.

As discussed above, the data processor 108 determines the bandpass energy of the focus plus signal and the focus minus signal to determine the proper positioning of the slide 104 so that the image signals will be representative of a focused image of the specimen on the slide. Accordingly, the data processor 108 includes first and second identical focus processor circuits 400 and 402 illustrated in Figure 4. The focus processor circuits 400 and 402 each include a band pass filter 404 and 406, respectively, for receiving the focus plus and focus minus signals. The band pass filters 404 and 406 are constructed to pass a band-pass energy component of the focus plus and focus minus signals. Each filtered signal is multiplied by itself in respective multiplier circuits 408 and 410 so that the resulting signal is always proportional to the magnitude of the energy . This energy level signal is then integrated for each line of active video provided in respective integrator 412 and 414 to provide signals indicative of the total energy provided in the band-pass. The output from the integrator 412 and 414 is sampled by respective sample and hold circuits 416 and 418 before being digitized by an analog-to-digital convertor 420. The data processor 108 uses the signals from the analog-to-digital convertor 420 to determine the proper positioning of the slide 104 so that the image signals provided by the primary camera 314 will be representative of a focused image.

The correction unit 502 of the data processor 108 is provided for correcting the image signal for pixel-to-pixel variation in amplification and leakage current.

A more detailed description of the data processor 108 is provided in Figure 5. Therein, the data processor 108 is shown to include a receiver/multiplexer 500 for receiving the image signal, focus plus signal, and focus minus signal. The receiver/multiplexer 500 is constructed to couple the image signal to a correction unit 502 for correcting the image signal for pixel-to-pixel variation, as will be described in more detail below. The receiver/multiplexer 500 further couples the focus plus and focus minus signals to focus processor circuits 400 and 402, discussed above. The light signal from the sensor 116 is coupled to an energy detector 504 for determining the energy provided by the flash of light from the strobe unit 114 and providing an energy signal indicative of its magnitude. The energy signal from the energy detector 504 is coupled to the reference input of an analog digital converter 506. The analog digital convertor 506 is also coupled to receive image signals from the correction unit 502 and to provide digital signals indicative of their magnitude by coupling the energy signals from the energy detector 504 to the reference input of the analog to digital convertor 506, the digital output will be automatically corrected for variation in the intensity of the flash of light provided by the strobe unit 114.

The digitized image signals from the analog to digital convertor 506 are provided to a memory unit 508. The memory unit 508 may comprise random access memory or any other memory for providing a conversion to the digitized image signals. The output from the random access memory 508 is selected by a multiplexer 514 as the output of the data processor 108. As illustrated, the multiplexor selects from the video signal from the random access memory 508 and predetermined video signals from a calibration unit 516. The calibration signals are used to determine the proper calibration of the data processor 108 for calibrating the video signal from the camera.

The data proceε or 108 also includes a timing and control circuit 512 for controlling the timing of the activation signals and the pulse and intensity signa-is. In accordance with a particularly novel aspect of the subject invention, a primary camera 314, capable of asynchronous operations, is selected so that the data processor 108 may control the time that the image signals are obtained, without waiting for the camera to be in synchronization with the motion controller 106. In operation, the motion controller 106 provides the position sign to the data processor 108 prior to the time th the motion controller 106 will position the ε„ide 104 in the position designated by the scan signal. The data processor 108 responds to the position signal to provide the activation signal to the primary camera 314, thereby synchronizing the primary camera 314 so that it will obtain an image when the motion controller arrives at the position designated by the scan signal. Thereafter, the data processor 108 provides the intensity and pulse signals to the strobe light 114 to illuminate the slide 104 at the time the motion controller 106 positions the slide at the designated position and the primary camera 314 begins obtaining the image signals. In a presently preferred embodiment of the invention, the motion controller 106 provides the position signal 61 milliseconds prior to the time it positions the slide at the designated position. The data processor 108 sets the timing to the primary camera 21 milliseconds prior to the time the motion controller positions the slide at the designated position and the intensity and pulse signals are provided to the strobe 114 at the time the motion controller positions the slide at the designated position.

The data processor 108 may further include a microprocessor, or other type processing device, for executing a predetermined set of instructions to perform a desired function. A particularly novel aspect of the subject invention is the method by which the focus plus and focus minus signals are combined to determine the proper focus of the camera. In operation, the data processor 108 receives an array of focus plus scores FP(0) , FP(1) , . . . FP(255) , and array of focus minus scores FM(0) , FM(1) , . . . FM(225) , each including 256 elements, one for each line of one field of the camera 102. The focus plus and focus minus array are each convolved with a filter array Ffk to correlate the energies of adjacent lines. The filter array is selected to provide a low pass filter that looks for objects at least five lines in size. The filter array Ffk is selected to provide a finite impulse response, low pass filtering of the focus plus and focus minus arrays. The filter kernel is designed to be sensitive to the size and type of object that the data processor 108 is attempting to detect. Further, the finite impulse response filtering is performed in a manner so that the resulting filter array eliminates the first and last few elements of the respective focus plus and focus minus array to eliminate edge effects from the filter.

After the focus plus and focus minus array have been filtered, filtered focus plus and focus minus arrays, F'P and F^,M, respectively, are created each including 252 elements. The filtered focus scores are further combined with a noise array to eliminate noise that may be provided by the camera system 100. More particularly, the camera system 100 may include noise that results from camera noise, integrator leakage, dust or streaks on the focus camera, or in one of the optical image planes. To eliminate this noise, a noise array is generated and combined with the filtered focus scores. The noise array is generated by focusing the camera 102 upon a white field, i.e., one with no slide 104 so that the focus plus and focus minus camera can measure the fixed noise floor energy within the focus filter band pass. This noise floor integration is relatively consistent and can be measured and subtracted from the energy measurements made for the individual line scores. This significantly improves the signal to noise ratio for each line.

In this regard, a noise plus and noise minus array is measured for the focus plus and focus minus camera, respectively, in the same manner as the focus plus and focus minus signals, discussed above. The noise plus and noise minus array include an element for each line of the focus plus and focus minus array, respectively. The noise plus and noise minus array is convolved with the filter array Ffk, as discussed above with the focus plus and focus minus arrays, to provide filtered noise plus and filtered noise minus, FNP and FNM arrays, respectively. The resulting array are filtered noise plus and noise minus arrays, having one to one correspondence with the focus plus and focus minus arrays, respectively. The noise plus and noise minus arrays are subtracted from the focus plus and focus minus arrays to provide respective focus plus and focus minus signal arrays, FPS and FPM, respectively.

The individual elements of the focus plus signal and the focus minus signal array are then combined to provide an array of focus scores FS, using the equation: FS(x) = [(FPS(x) FPM(x) )/(FPS(x) + FPM(x))]. This step produces a normalized focus score for each line of the camera 102, except the f.rst and last few lines that were excluded because of edge filter effects, as discussed above. Normalization of the focus scores helps to make the data independent, i.e., tends to make each score comparable to one another regardless of the amount of data used to produce the score.

After the focus plus signal array and focus minus signal array have been combined as discussed above to produce an array of focus scores, the array of focus scores is screened to eliminate those scores for which insufficient data existed to achieve a meaningful score. This is done by eliminating each score FS(x) for which FPS(x) plus FMS(x) is outside the range of a predetermined threshold. The threshold range is selected empirically by the lowest signal content image of interest. In a preferred embodiment of the invention, the range is selected as between 3 and 240. Those skilled in the art will appreciate, however, that this range is only illustrative and that any range, including the full range, may be selected. The inventors envision, however, that the most favorable results will be obtained using between 1% and 95% of the range.

After the focus score has been obtained a look up table is consulted for determining the distance and direction of movement along the optical path necessary to bring the object into focus. As noted above, a particularly novel aspect of the subject invention is the ability of the data processor 108 to not only determine whether an image is in focus or out of focus, and not only determine the direction necessary to move the specimen to bring the image into focus, but to also determine the distance of motion necessary to bring the specimen into focus. By determining the exact displacement, and direction of displacement, necessary to bring the specimen into focus,- the data processor 108 may control the motion controller 106 to rapidly return to the position of any out of focus specimen and may provide the appropriate scan signal so that the motion controller will position the specimen to be in focus.

To determine the amount of displacement, a look up table is generated prior to obtaining any image signals. A test image is employed and placed on the motion controller and a plurality of test focus images obtained to provide a correlation between the focus scores and the amount and direction of displacement necessary for proper focus. In a presently preferred embodiment of the invention, the calibration to determine the displacement and direction correlation to focus scores is performed only once when the system is designed and remains the same so long as the component parts of the system are not disturbed. However, those skilled in the art will appreciate that the calibration to obtain data correlating the focus scores to the amount and direction of displacement may be performed at any time prior to obtaining image signals.

Using the above-described apparatus, focused image signals may be obtained in a very rapid manner. In a presently preferred embodiment of the invention, the motion controller 106 positions the slide 104 at a plurality of predetermined positions for obtaining image signals. After each image signal is obtained, the motion controller 106 immediately moves to obtain the next image signal. While the motion -.ontroller 106 is positioning the slide 104 to obt • I the next image signal, the data processor 108 determines whether the last obtained image signal was in focus and, if so, identifies the image signal as a focused image signal for use by the remainder of the system. However, if the image signal was not in focus, the data processor 108 determines the displacement and direction necessary for focus of the specimen. Thereafter, the data processor 108 instructs the motion controller 106 to return to the out of focus image and provides the necessary displacement information so that, when next obtained, the image will be in focus. Those skilled in the art will appreciate that this method of obtaining focused image signals is much quicker than the prior art method where the specimen cannot be moved before a focused image signal is obtained. Even when the data processor 108 must return to obtain a second image signal because the first image signal was out of focus, the entire process may be performed in less time than that required by the prior art systems to obtain a single focused image signal. Further, since the camera assembly 102 is constructed from asynchronous cameras, additional time is saved in obtaining focused image signals. Essentially, the only time delay for obtaining image signals is that necessary for the motion controller 106 to position the slide 104 and that necessary for the camera 102 to obtain the image signals.

Still further, as noted above, only a single field of the image signals need be used to determine focus. Since the even and odd field of image signals from the focus plus and focus minus cameras are interlaced, information from the odd field would be substantially duplicative of that obtained from the even field. Further, since the method of processing the focus plus and focus minus signals discussed above processes each line separately, prior to obtaining an overall focus score, . the subject method provides much more information than that provided by prior art methods, even though using only one field. Still further, since each line is normalized, filtered, and corrected for noise, prior to obtaining the overall score, each line is capable of making a substantially equal contribution to the focus determination, even though the content of the image signal may vary from line to line. Accordingly, the above-noted method for processing the focus plus and focus minus signals results in faster and more accurate determination of focus than prior art systems.

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 claims.

What is claimed is:

Claims

Claims 1. Apparatus for providing digital data representing an image of a specimem on a slide (104) , said apparatus comprising: a linear motion controller (106) including a stage for receiving the slide (104) , said linear motion controller (106) being responsive to a slide scan signal for moving said stage in a slide plane represented by X and Y directions, said linear motion controller (106) being further responsive to a slide focus signal for moving said stage in a direction normal to said slide plane, said linear motion controller (106) being further constructed to provide a position signal indicating the X, Y, and Z position of said stage; a strobe light (114) responsive to a pulse signal for providing a flash of light, said strobe light (114) being further responsive to an intensity signal for varying the intensity of the flash of light provided, said strobe light (114) being positioned to illuminate the slide (104) with the flash of light; photo detector means (116) , positioned to receive a portion of said flash of light, for providing a light signal indicative of the intensity of said flash of light; optical transmission means for providing first, second, and third images of the slide (104) along respective first, second, and third optical paths, said optical transmission means (110) being further constructed to vary the magnification provided to said first, second, and third magnified images of the slide (104) , said optical transmission means (110) being positioned relative to said stage of said linear motion controller (106) so that said slide focus signal moves said stage to vary the focal length between the slide (104) and said optical transmission means (110) ; primary camera means (314) , positioned along said first optical path for receiving said first image of the slide (104) from said optical transmission means (110) , for receiving the first magnified image provided by said optical transmission means (110) , said primary camera means (314) being responsive to an activation signal for providing an image signal representing the first magnified image; first focus camera means (316) , positioned along said second optical path for receiving said second image of the slide (104) from said optical transmission means (110) wherein the length of said second optical path is greater than the length of said first optical path by a predetermined length, said first focus camera means (316) being responsive to said activation signal for providing a focus plus signal indicative of the focus of said image signal; second focus camera means (318) , positioned along said third optical path for receiving said third image of the slide (104) from said optical transmission means (110) wherein the length of said third optical path is less than the length of said first optical path by said predetermined length, said second focus camera means (318) being responsive to said activation signal for providing a focus minus signal indicative of the focus of said image signal; focus signal processor (400) means for determining the relative high frequency components of said focus plus and focus minus signals to provide an array of focus plus signals and an array of focus minus signals wherein each element in the array is indicative of the high frequency component of a line from said first and second focus cameras, respectively; data processor means (108) responsive to said array of focus plus signals and said array of focus signals for providing said slide focus signal to move said slide (104) along said first optical path so that said image signal is in focus, said data processor means (108) being further responsive to said light signal for providing said intensity signal to modulate the intensity of said flash of light, said data processor means (108) being further constructed for providing said pulse signal and said activation signal to illuminate the slide (104) and to obtain said image signal, said focus plus signal and said focus minus signal,^' said data processor means (108) including image processor means (420) for receiving said image signal and being responsive to said light signal for altering said image signal to correct for variations in the intensity of said flash of light, said data processing means (108) further including memory means (508) for storing said slide focus signal and said position signal, said data processing means (108) being further constructed to determine when a non-focused image signal is provided that is not representative of a focused image of portion of the specimen and for providing said scan signal, said activation signal, said pulse signal and said slide focus signal to obtain an image signal representative of a focused image of the portion of the specimen that was obtained by said non-focused image signal.

2. The apparatus as recited in claim 1 wherein said image processor means (420) comprises an analog to digital converter for providing a digital signal indicative of the magnitude of said image signal, said analog to digital converter (420) including a reference input coupled to receive said light signal to that the digital output provided is a function of the magnitude of said image signal and said light signal.

3. Apparatus for providing a signal representing a focused image of an object, said apparatus comprising: camera means (102) for providing an image signal indicative of the image of the object, wherein said camera means (102) is responsive to a focus signal for * reusing said camera means (102) on a focal point, said camera means (102) being further constructed for providing an offset focus signal by focusing said camera means (102) on an offset focal point displaced from said focal point by a predetermined distance; focus signal processor (400) means for determining the high frequency component of said offset focus signal to provide said focus signal so that said focal point will be positioned substantially coincident with the object and so that said image signal provided by said camera means (102) will be representative of a focused image of the object.

4. The apparatus as recited in claim 3 wherein said camera means (102) comprises: a primary camera (314) focused on said focal point for providing said image signals, said focal point being positioned along a predetermined optical path between said primary camera (314) and said focal point; an offset focus camera (316, 318) focused on said offset focal point for providing said offset focus signal, said offset focal point being positioned along a first optical path between said offset focus camera (316, 318) and said offset focal point wherein the length of said first optical path is greater than the length of said predetermined optical path.

5. The apparatus as recited ix claim 4 further comprising object positioning means (106) for positioning the object, said object positioning means (106) being responsive to the focus signal for moving said object along said predetermined optical path to alter the focus of said primary camera (314) and said offset camera.

6. The apparatus as recited in claim 3 wherein said camera means (102) further comprises means for providing a focus plus signal and a focus minus signal by focusing said camera means (102) on respective focus plus and focus minus focal points positioned a predetermined distance from the object wherein said focus plus signal and said focus minus signal comprise said offset focus signal.

7. The apparatus as recited in claim 6 wherein said camera means (102) comprises: a primary camera (314) focused on said focal point for providing said image signals, said focal point being positioned along a predetermined optical path between said primary camera (314) and said focal point; a focus plus camera (316) focused on said focus plus focal point for providing said focus plus signal, said focus plus focal point being positioned along a first optical path between said focus plus camera (316) and said focus plus focal point wherein the length of said first optical path is greater than the length of said predetermined optical path; and a focus minus camera (318) focused on said focus minus focal point for providing said focus minus signal, said focus minus focal point being positioned along a second optical path between said focus minus camera (318) and said focus minus focal point wherein the length of said second optical path is less than the length of said predetermined optical path.

8. The apparatus as recited in claim 7 further comprising object positioning means (106) for positioning the object, said object positioning means (106) being responsive to the focus signal for moving said object along said predetermined optical path to alter the focus of said primary camera (314) , said focus plus camera (316) and said focus minus camera (318) .

9. The apparatus as recited in claim 3 wherein said focus signal processor (400) means further comprises a focus processor circuit (400) for providing an array of offset signals, each indicative (504) of the high frequency energy provided from a line of said offset focus signal, said focus processor circuit (400) (316, 318) including means for storing a noise array and for combining the noise array with the offset array to provide said focus signal.

10. The apparatus as recited in claim 6 wherein said focus signal processor (400) means further comprises first and second focus processor circuits (400) for providing first and second signals indicative (504) of the high frequency energy provided in said focus plus signal and said focus minus signal, respectively, said focus processor circuits (400) each including a filter for selecting a predetermined frequency band of said focus plus signal and said focus minus signal, respectively, each of said first and second focus processor circuits (400, 402) further including apparatus for determining the energy (504) provided by the portion of their respective focus plus and focus minus signal having a frequency within the predetermined frequency band.

11. The apparatus as recited in claim 10 wherein s~id fc•us signal processor (400) means further comprises means for determining the difference between the output from said first and second focus processor circuits (400, 402) .

12. Apparatus for providing a signal representing an image of an object, said apparatus comprising: light means (114) for providing light to illuminate the object and for providing a light signal indicative of the intensity of said light; camera means (102) for providing an image signal indicative of the image of the object; and data processing means (108) responsive to said light signal for altering said image signal so that said image signal is corrected for variations in the intensity of said light.

13. The apparatus as recited in claim 12 wherein said camera means (102) is responsive to an activation signal for providing said image signal, said light means (114) further comprising a strobe light (114) responsive to a pulse signal for providing a flash of light, wherein said data processing means (108) is constructed to provide said pulse signal and said activation signal so that the object is illuminated when said image signal is provided.

14. The apparatus as recited in claim 13 wherein said data processing means (108) comprises an analog to digital converter (420) having an analog input for receiving the image signals and a reference input for receiving said light signal, said analog to digital output providing the atered image signals.

15. The apparatus as recited in claim 12 wherein said camera means (102) further comprises means responsive to a focus signal for focusing said camera means (102) on a focal point, said camera means (102) being further constructed for providing an offset focus signal by focusing said camera means (102) on an offset focal point displaced from said focal point by a predetermined distance.

16. The apparatus as recited in claim 15 further comprising: focus signal processor (400) means for ^' determining the high frequency component of said offset focus signal to provide said focus signal so that said focal point will be positioned substantially coincident with the object and so that said image signal provided by said camera means (102) will be representative of a focused image of the object.

17. The apparatus as recited in claim 16 wherein said camera means (102) composes: a primary camera (314) focused on said focal point for providing said image signals, said focal point being positioned along a predetermined optical path between said primary camera (314) and said focal point; an offset focus camera (316, 318) focused on said offset focal point for providing said offset focus signal, said offset focal point being positioned along a first optical path between said offset focus camera (316, 318) and said offset focal point wherein the length of said first optical path is greater than the length of said predetermined optical path.

18. The apparatus as recited in claim 17 further comprising object positioning means (106) for positioning the object, said object positioning means (106) being responsive to the focus signal for moving said object along said predetermined optical path to alter the focus of said primary camera (314) and said offset camera.

19. The apparatus as recited in claim 16 wherein said camera means (102) further comprises means for providing a focus plus signal and a focus minus signal by focusing said camera means (102) on respective focus plus and focus minus focal points positioned a predetermined distance from the object wherein said focus plus signal and said focus minus signal comprise said offset focus signal.

20. The apparatus as recited in claim 19 wherein said camera means (102) comprises: a primary camera (314) focused on said focal point for providing said image signals, said focal point being positioned along a predetermined optical path between said primary camera (314) and said focal point; a focus plus camera (316) focused on said focus plus focal point for providing said focus plus signal, said focus plus focal point being positioned along a first optical path between said focus plus camera (316) and said focus plus focal point wherein the length of said first optical path is greater than the length of said predetermined optical path; and a focus minus camera (318) focused on said focus minus focal point for providing said focus minus signal, said focus minus focal point being positioned along a second optical path between said focus minus camera (318) and said focus minus focal point wherein the length of said second optical path is less than the length of said predetermined optical path.

21. The apparatus as recited in claim 20 further comprising object positioning means (106) for positioning the object, said object positioning means (106) being responsive to the focus signal for moving said object along said predetermined optical path to alter the focus of said primary camera (314) , said focus plus camera (316) and said focus minus camera (318) .

22. The apparatus as recited in claim 16 wherein said focus signal processor (400) means further comprises a focus processor circuit (400, 402) for providing a signal indicative (504) of the high frequency energy provided in said offset focus signal, said focus processor circuit (400, 402) including a filter (404) for selecting a predetermined frequency band of said offset focus signal and apparatus (408, 412, 416) for determining the energy (504) provided by the portion of the offset focus signal having a frequency within the predetermined frequency band.

23. The apparatus as recited in claim 19 wherein said focus signal processor (400) means further comprises first and second focus processor circuits (400, 402) for providing first and second signals indicative (504) of the high frequency energy provided in said focus plus signal and said focus minus signal, respectively, said focus processor circuits (400, 402) each including a filter (404, 406) for selecting a predetermined frequency band of said focus plus signal- and said focus minus signal, respectively, each of said first and second focus processor circuits (400, 402) further including apparatus for determining the energy (504) provided by the portion of their respective focus plus and focus minus signal having a frequency within the predetermined frequency band.

24. The apparatus as recited in claim 23 wherein said focus signal processor (400) means further comprises means for determining the difference between the output from said first and second focus processor circuits (400, 402) .

25. A method for focusing a camera (102) on a focus plane comprising the steps of:

(a) providing (316) a focus plus array of signals and a focus minus array of signals wherein each element of the focus plus and focus minus arrays are indicative of signals received from line of a camera (102) focused on planes displaced from the focus plane;

(b) filtering (404) the focus plus and focus minus array of signals with a predetermined filter array (404) to provide respective filtered focus plus and filtered focus minus arrays, wherein the filter array (404) is selected to correlate the effects of signals received from adjacent lines of the focus plus and focus minus array; (c) combining the filtered focus plus array

(404, 406) and the filtered focus minus array (404, 406) to provide an array of focus scores wherein the filtered arrays (404, 406) arrays are combined in a manner so that the array of focus scores are normalized; and

(d) using the array of normalized focus scores to determine the proper focus of the camera (102) .

26. The method as recited in claim 25 further comprising the steps of:

(e) using only the normalized focus scores that fall within a predetermined range indicating that they were generated from a predetermined range of energy.

27. The method as recited in claim 26 further comprising the steps of:

(f) generating a noise plus and noise minus array of signals;

(g) filtering (404) the noise plus and noise minus array of signals using the filter array (404,

406) ; and

(h) subtracting the noise plus and noise minus arrays from the filtered focus plus and filtered minus arrays.

28. The method as recited in claim 25 wherein step (d) , using the array of normalized focus scores to determine the proper focus of the camera (102) , comprises the sub steps of: (i) correlating the focus scores with a magnitude and direction of displacement so that the direction and amount of movement necessary to move the camera (102) into focus is provided by the correlated data.

29. A method for obtaining image data representing a plurality of images comprising the steps of:

(a) moving apparatus (106) for obtaining the image data to a first predetermined location and obtaining the image data corresponding to that location;

(b) moving the apparatus (106) for obtaining the image data to a second predetermined location and obtaining the image data corresponding to that location;

(c) after beginning step (b) , determining whether the image data from the first predetermined location represents a focused image and, if so, identifying the data as a focused image and, if not, performing step (d) ; and

(d) determining the proper positioning of the apparatus for obtaining the image data to obtain a focused image and returning to the first predetermined position to obtain focused image signals.

30. The method as recited in claim 29 wherein step (d) , determining the proper positioning of the apparatus for obtaining the image data, comprises the sub steps of: (e) providing (316, 318) a focus plus array of signals and a focus minus array of signals wherein each element of the focus plus and focus minus arrays are indicative of signals received from line of a camera (102) focused on planes displaced from the focus plane;

(f) filtering (404, 406) the focus plus and focus minus array of signals with a predetermined filter array (404, 406) to provide respective filtered focus plus and filtered focus minus arrays, wherein the filter array (404, 406) is selected to correlate the effects of signals received from adjacent lines « ^" the focus plus and focus minus array; (g) combining the filtered focus plus array and the filtered focus minus array to provide an array of focus scores wherein the filtered arrays (404, 406) are combined in a manner so that the array of focus scores are normalized; and (h) using the array of normalized focus scores to determine the proper focus of the camera (102) .

31. The method as recited in claim 29 wherein step (a) , moving apparatus for obtaining the image data (106) to a first predetermined location and obtaining the image data corresponding to that location, comprises the sub steps of:

(i) providing a position signal, indicating that the object to be imaged will be properly positioned relative to a camera (102) for obtaining the image signals, a first predetermined time prior to the object being properly positioned; and

(j) responding to the position signal to provide an activation signal to the camera (102) a second predetermined time prior to the time that the object is properly positioned, wherein the activation signal controls the camera (102) to begin obtaining the image signals when the object is properly positioned.