GB1571404A - Image processing system - Google Patents

Description

(54) IMAGE PROCESSING SYSTEM (71) We, OLYMPUS OPTICAL COM- PANY LIMITED, a company organized according to the laws of Japan, of No. 43-2, 2-Chome, Hatagaya, Shibuya-Ku, Tokyo, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to an image processing system for providing information of optical density variations in a television image.

In the technical field of carrying out morphological study on samples such as cells, it Is known for and image of such samples to be observed through a microscope and to be picked up by a television camera (hereinafter referred to as TV camera). The optical density of the microscope image is coded from its video signal and written into the memory of a computer, and a pattern having an optical density greater than a selected threshold value is identified. Certain properties of such a pattern of relatively high optical density may then be derived from the computer.

Fig. 1 of the drawings shows a block diagram illustrating one embodiment of a conventional image processing system, in which a microscope image of, for example, a cell sample obtained by a microscope 10 is converted into an electric video signal by a TV camera 14. The TV camera 14 receives horizontal and vertical synchronizing signals from a synchronizing signal generator 12, and the thus converted video signal is suppled to an analog-digital converting device 18 (hereinafter referred to as A-D converting device ) through an image signal pickup device 16. The A-D converting device 18 effectively divides the signal into a plurality of levels of optical density thereof and provides a digital code for each level, the resulting coded signal then being supplied to a computer 22 through an interface 20.

A timing signal from the synchronizing signal generator 12 is supplied as a synchronizing signal to the image signal pickup device 16 and is also supplied to a control device 24, from which may be derived the positional co-ordinates of a visual field of the TV camera 14. The timing signal is furthermore utilized for controlling timing of the sample and hold function of the A-D converting device 18 and timing of data written into the computer 22 through the interface 20. The control device 24 is responsive to an image receiving program from the computer 22 through the interface 20, and thereby provides the above timing functions. Thus, the computer 22 successively reads in the optical densities of line scans of the image from the TV camera into the memory under the control of the control device 24 in accordance with a particular program. In general, the scanning of the X-coordinates and Y-coordinates of the microscope image is carried out by the TV camera 14, the optical densities of the image obtained by the TV camera 14 being coded to be written into the memory of the computer 22, and then patterns having optical densities greater than a certain value may be analysed by the computer or some other processing may be carried out.

In order to code the optical density of the television image, each field is subdivided into a number of discrete areas, for example using a TV camera of the NTSC system, the subdivision per field is about 500 in the horizontal direction (X) and about 500 in the vertical direction (Y), i.e., 500 x 500 250,000, and the optical density of each image element is coded and transmitted to the computer.

However, if for example the optical density of one image element is expressed as a 6 bit word, the quantity of information required to be stored is very large, i.e. 6 x 250,000 = 1.5 x 106 bits, so that a computer having a very large memory capacity is required. Further, one horizontal line scan of the TV camera is performed in 63.5 micro seconds in the NTSC system, so that about 500 image elements need to be subdivided within this time. Therefore, in the above-described system, the sample and hold circuit, the analog-digital converting circuit and other processing units must be operated very quickly, and such fast, opera- tion is very difficult to implement. Accordingly, the conventional image processing system requires a computer having a large memory capacity and circuits capable of very high speed operation, these requirements considerably adding to the expense of the system.

It has been found that when carrying out a morphological analysis of samples such as cells or of general samples such as metallic materials, an effective analysis can be carried out by considering variations in optical density over the whole sample. For example, in the case of a live system, for example a cell viewed as a sample under a microscope, such a sample may be treated as a phase object in optics, the image input being treated with a phase difference microscope.

If it is desired to treat the analysis of the image in terms of optical density changes instead of considering the optical density of the whole image it has previously been necessary to use an expensive image processing system as shown in Fig. 1, the optical densities of the whole image being supplied to the computer and optical density changes subsequently being determined by an appropriate program.

The present invention provides an image processing system comprising a microscope for observing a sample, a television camera optically coupled to the microscope and arranged to convert the microscope image of the sample into a television signal which includes an image signal component representative of optical density variations in line scans of said image and a synchronizing signal component, means arranged to separate the image signal component from the television signal, quantizing means connected to said separating means and arranged to quantize said image signal component to produce a series of pulses resulting from values of said image signal component greater than a threshold value, counting means arranged to count the number of pulses produced by said quantizing means during each line scan, and means arranged to transfer the count accumulated in said counting means to a computer at the end of each line scan.

In the preferred embodiment of the present invention, a number indicative of optical density changes within each line scan is derived and transferred to the computer, instead of coding the optical density of each image element separately.

In order that the present invention may be more readily understood, an embodiment thereof will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a block diagram showing a conventional image processing system; Fig. 2 is a block diagram showing one embodiment of the image processing system according to the present invention; Fig. 3 is a signal waveform diagram explaining the operation of the image processing system shown in Fig. 2; Fig. 4 is a block diagram showing a circuit which may form part of the system shown in Fig. 2; Fig. 5 is a block diagram showing a further circuit which may form another part of the system shown in Fig. 2; and Fig. 6 is a block diagram showing a circuit for obtaining a coordinate value signal in the vertical scanning direction (Y-axial direction) for use in the system shown in Fig. 2.

Referring to Fig. 2, one embodiment of an image processing system according to the present invention is shown. Similar reference characters refer to similar member or devices shown in Fig. 1. An image from a microscope 10 is converted into a common television image signal, as shown in Fig. 3A, by a TV camera 14, a synchronizing signal generator 12 and an image signal pickup device 16 and transmitted to a preprocessing circuit 30. The pre-processing circuit 30 is provided for emphasizing selected frequency components of the image signal, so that if for example this circuit comprises a differentiating circuit having a small time constant, only high frequency components are present at the output of the circuit 30. The image signal thus treated by the pre-processing circuit 30 is fed to an image signal selection and amplifying circuit 32 in which the image information component is separated from the synchronizing signals and any other signal not representative of optical density of the image, the image information component being amplified and supplied to a wave shaping circuit 34 as a signal having the waveform shown in Fig. 3D. The wave shaping circuit 34 converts this signal into a rectangular wave shown in Fig. 3E by quantizing the signal shown in Fig. 3D with reference to a selected threshold level, and further converts the rectangular wave into a pulse signal shown in Fig. 3F. The thus obtained pulse signals, which are indicative of the number of optical density changes, are supplied to a digital counter 36 to count the number of pulse signals. The count in the digital counter 36 is supplied to the compu ter 22 through the interface 20 and successively written into the memory of the computer 22. In Fig. 2, reference numeral 38 indicates a timing signal generating circuit which generates timing and gate signals, and an interrupt pulse to the interface 20 as hereinafter described. These various signals are derived from the synchronizing signal generating device 12 and from the image signal pickup device 16 using the synchronizing signal (Fig. 3B) separated from the image signal. The image signal selection and amplifying circuit 32 is supplied with a gate signal shown in Fig. 3C timed to correspond to the period of the image information component of the image signal. The wave shaping circuit 34 is supplied with a gate signal shown in Fig. 3H for enabling quantization of a selected portion of each horizontal line scan, and the digital counter 36 is supplied with a reset signal (horizontal synchronizing signal shown in Fig. 3B).

Accordingly, in practice the digital counter 36 counts the number of pulses from the wave shaping circuit 34 which is under the control of gate signals (shown in Fig. 3H) from the timing signal generating circuit 38.

After completion of each horizontal line scan an interrupt pulse is transmitted from the timing signal generating circuit 38 to the interface 20, to enable the count in the digital counter 36 at the end of every horizontal line scan to be transmitted to the computer.

The pulse signal shown in Fig. 3G comprises a series of clock pulses synchronized with the gate signal shown in Fig. 3C, so that timing is carried out by this pulse signal for the image information component in the image signal. The clock pulses may be counted for every horizontal line scan and may generate a gate signal only during the period when the count is between selected limits. and this gate signal may be used to obtain a selected portion of each horizontal line scan as described hereinafter. The gate signal can enable gating of a selected portion, i.e., region, of one horizontal line scan, so that it is referred to as a "region gate signal" hereinafter. In the embodiment shown in Fig. 2, this region gate signal is formed by part of the timing signal generating circuit 38, and a suitable circuit for this function is shown in greater detail in Fig. 4.

In Fig. 4. reference numeral 40 indicates a clock pulse generator, 42 a clock pulse counting circuit for counting clock pulses from the clock pulse generator 40, 44 a comparison circuit for comparing the count in the clock pulse counting circuit 42 with inputs indicative of a region upper limit value and a region lower limit value applied through terminals 46 and 48. This region gate signal is generated at output terminal 50 when the count in the clock pulse counting circuit 42 is between the region lower limit value and the region upper limit value.

An image signal input terminal 52 receives an image signal from the image signal pickup device 16 shown in Fig. 2, and a horizontal synchronizing signal separating circuit 54 separates the horizontal synchronizing signal from the image signal and supplies the thus separated synchronizing signal as a reset signal to the clock pulse counting circuit 42. The clock pulse counting circuit 42 starts counting clock pulses from the start of each horizontal line scan and is reset by the following horizontal synchronizing signal, so that as described above, only when the count in the clock pulse counting circuit 42 is between the region lower limit value and the region upper limit value, is the region gate signal (as shown in Fig. 3H) obtained from the output 50 of the comparison circuit 44, in order to gate the selected portion of each horizontal line scan. The region lower limit value and the region upper limit value are set for each horizontal line scan in accordance with the program of the computer 22 and are supplied to the terminals 46 and 48 through the interface 20.

The circuit shown in Fig. 5 may be used as the image signal selection and amplifying circuit 32 shown in Fig. 2. Referring to Fig.

5, a gate signal input terminal 60 is connected to one output of the timing signal generating device 38 (Fig. 2), an image signal input terminal 62 is connected to the output of the pre-processing circuit 30 (Fig.

2), and an analog switch 64 is switched on or off by the gate signal at input terminal 60.

An amplifier 66 is connected to an input resistance Rj and a feedback resistance Rf.

The analog switch 64 is connected in parallel with the feedback resistance Rf, so that when the gate signal is supplied to the terminal 60, the switch 64 is in the cut-off state, and when the gate signal is not supplied thereto, it is in the on state and the feedback resistance Rf is short-circuited. Accordingly, the amplifier 66 is operated as an amplifier having Rf/Rj times the amplification when the analog switch 64 is in the off state, while the amplification becomes 0 times (that is, the output is 0) when the analog switch 64 is in the on state. Therefore, when the gate signal shown in Fig. 3C is supplied to the gate signal input terminal 60, the image signal being supplied to the terminal 62, only the image information component thereof is amplified, so that the signal shown in Fig. 3D is obtained at the output terminal 68. Alternative methods of extracting only the image information component from the image signal shown in Fig. 3A would include either switching the output of an amplifier or the input of an amplifier, rather than switching the feedback path as shown in Fig.

5.

The coordinate value in the Y-direction (vertical scanning direction) can be defined by, for example, the circuit shown in Fig. 6 which may form part of the image signal pickup device 16. The image signal as shown in Fig. 3A is supplied to a horizontal synchronizing separation circuit 72 via a terminal 70 to extract the horizontal synchronizing signal (Fig. 3B) and pulses in the synchronizing signal are counted by a vertical coordinate counting circuit 74. The counting circuit 74 is reset by a vertical synchronizing signal derived from the image signal at the end of each field by a vertical synchronizing separation circuit 76, therefore the vertical coordinate counting circuit 74 counts a number of horizontal line scans for each vertical synchronizing signal so that the coordinate value in the Y-direction can be obtained.

The prepared embodiment includes the pre-processing circuit 30 and if a differentiating circuit having a small time constant is used as the pre-processing circuit 30 as described above, only the high frequency component of the optical density changes is extracted. If the focussing of the TV camera is so controlled that the number of optical density changes, i.e., the count value in the digital counter 36 is made to be a maximum, an automatically focussed system can be provided since a fully focussed image produces a maximum of optical density changes in the image. It is furthermore possible to arrange the threshold level of the wave shaping circuit 34 at such a level that any foreign matter having abnormally high optical densities can be detected.

An image processing system as hereinbefore described does not require circuits such as the sample and hold circuit, the A-D converting device, or the control device of the previously proposed systems which, being either analog processing elements or digital elements capable of high speed operation, tend to be expensive, and the present system can be composed of comparatively technically simple and inexpensive circuits to form the image selection and amplifying circuit, the quantizing circuit (which may conveniently be a Schmitt trigger circuit), the counting circuit and the timing signal generating circuit. It thus becomes possible to allot sufficient time, such as 63.5 micro seconds per data, for transfer of data to the computer and circuits with slower operating speeds can be used. Further, the data number to be read is limited to a maximum of e.g. 525 (in the NTSC system) being the number of horizontal line scans per field, so that the reading time can be decreased, and the processing program of the computer becomes comparatively simple. Accordingly, apparatus according to the present invention can provide an inexpensive image processing system.

WHAT WE CLAIM IS: 1. An image processing system comprising a microscope for observing a sample, a television camera optically coupled to the microscope and arranged to conver the microscope image of the sample into a television signal which includes an image signal component rep:-esentative of optical density variations in line scans of said image and a synchronising signal component, means arranged to separate the image signal component from the television signal, quantizing means connected to said separating means and arranged to quantize said image signal component to produce a series of pulses resulting from values of said image signal component greater than a threshold value, counting means arranged to count the number of pulses produced by said quantizing means during each line scan, and means arranged to transfer the count accumulated in said counting means to a computer at the end of each line scan.

2. An image processing system according to claim 1 wherein said separating means includes a pre-processing circuit which comprises a differentiating circuit.

3. An image processing system according to claim 1 or 2 wherein said separating means includes switch means responsive to a gating signal to inhibit passage of the synchronizing signal component of the television signal.

4. An image processing system according to claim 3 wherein said separating means further includes an amplifier provided with a feedback path and arranged to receive the television signal, said switch means being arranged to selectively short-circuit the feedback path of the amplifier in response to the gating signal.

5. An image processing system according to any one of the preceding claims further including portion selecting means arranged such that only a selected portion of each line scan is processed.

6. An image processing system according to claim 5 wherein said portion selecting means comprises comparison means arranged to receive lower and upper limit signals indicative of lower and upper limits of the selected portion of each line scan.

7. An image processing system according to claim 6 wherein said portion selecting means further includes a counter for counting clock pulses fed thereto, said count being received by said comparison means and an enabling signal being produced by said comparison means only when the count is between the values of said lower and upper limit signals.

8. An image processing system according to claim 7 wherein said enabling signal is fed to said quantizing means to enable quan

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. (vertical scanning direction) can be defined by, for example, the circuit shown in Fig. 6 which may form part of the image signal pickup device 16. The image signal as shown in Fig. 3A is supplied to a horizontal synchronizing separation circuit 72 via a terminal 70 to extract the horizontal synchronizing signal (Fig. 3B) and pulses in the synchronizing signal are counted by a vertical coordinate counting circuit 74. The counting circuit 74 is reset by a vertical synchronizing signal derived from the image signal at the end of each field by a vertical synchronizing separation circuit 76, therefore the vertical coordinate counting circuit 74 counts a number of horizontal line scans for each vertical synchronizing signal so that the coordinate value in the Y-direction can be obtained. The prepared embodiment includes the pre-processing circuit 30 and if a differentiating circuit having a small time constant is used as the pre-processing circuit 30 as described above, only the high frequency component of the optical density changes is extracted. If the focussing of the TV camera is so controlled that the number of optical density changes, i.e., the count value in the digital counter 36 is made to be a maximum, an automatically focussed system can be provided since a fully focussed image produces a maximum of optical density changes in the image. It is furthermore possible to arrange the threshold level of the wave shaping circuit 34 at such a level that any foreign matter having abnormally high optical densities can be detected. An image processing system as hereinbefore described does not require circuits such as the sample and hold circuit, the A-D converting device, or the control device of the previously proposed systems which, being either analog processing elements or digital elements capable of high speed operation, tend to be expensive, and the present system can be composed of comparatively technically simple and inexpensive circuits to form the image selection and amplifying circuit, the quantizing circuit (which may conveniently be a Schmitt trigger circuit), the counting circuit and the timing signal generating circuit. It thus becomes possible to allot sufficient time, such as 63.5 micro seconds per data, for transfer of data to the computer and circuits with slower operating speeds can be used. Further, the data number to be read is limited to a maximum of e.g. 525 (in the NTSC system) being the number of horizontal line scans per field, so that the reading time can be decreased, and the processing program of the computer becomes comparatively simple. Accordingly, apparatus according to the present invention can provide an inexpensive image processing system. WHAT WE CLAIM IS:

1. An image processing system comprising a microscope for observing a sample, a television camera optically coupled to the microscope and arranged to conver the microscope image of the sample into a television signal which includes an image signal component rep:-esentative of optical density variations in line scans of said image and a synchronising signal component, means arranged to separate the image signal component from the television signal, quantizing means connected to said separating means and arranged to quantize said image signal component to produce a series of pulses resulting from values of said image signal component greater than a threshold value, counting means arranged to count the number of pulses produced by said quantizing means during each line scan, and means arranged to transfer the count accumulated in said counting means to a computer at the end of each line scan.

2. An image processing system according to claim 1 wherein said separating means includes a pre-processing circuit which comprises a differentiating circuit.

3. An image processing system according to claim 1 or 2 wherein said separating means includes switch means responsive to a gating signal to inhibit passage of the synchronizing signal component of the television signal.

4. An image processing system according to claim 3 wherein said separating means further includes an amplifier provided with a feedback path and arranged to receive the television signal, said switch means being arranged to selectively short-circuit the feedback path of the amplifier in response to the gating signal.

5. An image processing system according to any one of the preceding claims further including portion selecting means arranged such that only a selected portion of each line scan is processed.

6. An image processing system according to claim 5 wherein said portion selecting means comprises comparison means arranged to receive lower and upper limit signals indicative of lower and upper limits of the selected portion of each line scan.

7. An image processing system according to claim 6 wherein said portion selecting means further includes a counter for counting clock pulses fed thereto, said count being received by said comparison means and an enabling signal being produced by said comparison means only when the count is between the values of said lower and upper limit signals.

8. An image processing system according to claim 7 wherein said enabling signal is fed to said quantizing means to enable quan

tizing of said image signal component over said selected portion.

9. An image processing system substantially as hereinbefore described with reference to Figures 2, 3, 4, 5 and 6 of the accompanying drawings.