METHOD FOR CORRECTING A COLOR REPRODUCTION OF A DIGITAL MICROSCOPE AND DIGITAL MICROSCOPEE

Abstract

A method for correcting colors of a color reproduction of a digital microscope and a digital microscope are described. In a first step of a method according to the invention, a color image of a sample that is to be examined under the microscope is recorded. When the recording is performed, wavelength-dependent properties of a microscope illumination unit that illuminates the sample are determined in order to describe a state of the microscope illumination unit, in that settings selected at the microscope illumination unit are captured. A set of correction values is determined, which is associated with a state of the microscope illumination unit that is selected in accordance with the state of the microscope illumination unit determined when the recording is performed. In a further step, the colors of the recorded color image of the sample are corrected by applying the correction values of the previously determined set.

Claims

1. A method for correcting colors of a color reproduction of a digital microscope, comprising the following steps: recording a color image of a sample that is to be examined under the microscope, wherein wavelength-dependent properties of a microscope illumination unit illuminating the sample are determined for describing a state of the microscope illumination unit by capturing settings selected on the microscope illumination unit; identifying a set of correction values associated with a state of the microscope illumination unit, wherein the state of the microscope illumination unit associated with the set of correction values that is to be determined is selected based on the determined state of the microscope illumination unit; and correcting the colors of the recorded color image by way of the correction values of the previously determined set.

2. The method according to claim 1, wherein: when recording the color image of the sample that is to be examined under the microscope, furthermore, wavelength-dependent properties of an optical recording device of the microscope comprising an optical system and an image converter are determined in order to describe a state of the optical recording device through the capturing of the selected settings on the optical recording device; and wherein the set of correction values to be determined is further associated with a state of the optical recording device, wherein the state of the optical recording device associated with the set of the correction values to be determined is selected according to the determined state of the optical recording device.

3. The method according to claim 1, wherein the identification of a set of correction values comprises a partial step in which at least one set of correction values is selected from a plurality of sets of correction values associated with stored and different states of the optical microscope illumination unit, wherein the state of the microscope illumination unit associated with the selected set of correction values most closely approximates the determined state of the microscope illumination unit.

4. The method according to claim 3, wherein the selected set of correction values is used as the set of correction values to be determined.

5. The method according to claim 3, wherein the identification of a set of correction values furthermore comprises a partial step in which the correction values of the selected set are adjusted if the state of the microscope illumination unit associated with the selected set of correction values is not fully identical to the determined state of the microscope illumination unit.

6. The method according to claim 3, at least two of the sets of correction values are selected from the plurality of sets of correction values associated with stored and different states of the microscope illumination unit, wherein the identification of a set of correction values furthermore comprise a partial step in which the correction values of the two selected sets are interpolated.

7. The method according to claim 3, wherein the sets of correction values associated with the stored and different states of the microscope illumination unit are determined by way of the following partial steps: capturing the wavelength-dependent properties of the microscope illumination unit in the multiple states of the microscope illumination unit by associating the selected settings on the microscope illumination unit; recording a color image of a color reference with the digital microscope in each of the multiple states of the microscope illumination unit; and determining respective sets of correction values for each of the multiple states of the microscope illumination unit, which described the correction of the image recorded in the respective state of the microscope illumination unit for the true-color reproduction the color reference.

8. The method according to claim 1, wherein determining a set of correction values is accomplished by way of a calculation, taking into account the wavelength-dependent properties of the microscope illumination unit illuminating the sample.

9. The method according to claim 1, wherein the settings selected on the microscope illumination unit are captured due to the spectral measurement of the illumination light emitted by the microscope illumination unit by means of a wavelength-sensitive sensor.

10. A digital microscope, comprising an optical recording device, a microscope illumination unit, and an image processing unit configured for the execution of the method according to claim 1.

11. The method according to claim 1, wherein the identification of a set of correction values comprises a partial step in which at least one set of correction values is selected from a plurality of sets of correction values associated with stored and different states of the optical microscope illumination unit, wherein the state of the microscope illumination unit associated with the selected set of correction values most closely approximates the determined state of the microscope illumination unit.

12. The method according to claim 1, wherein determining a set of correction values is accomplished by way of a calculation, taking into account the wavelength-dependent properties of the microscope illumination unit illuminating the sample.

13. The method according to claim 2, wherein the settings selected on the microscope illumination unit are captured due to the spectral measurement of the illumination light emitted by the microscope illumination unit by means of a wavelength-sensitive sensor.

14. The method according to claim 3, wherein the settings selected on the microscope illumination unit are captured due to the spectral measurement of the illumination light emitted by the microscope illumination unit by means of a wavelength-sensitive sensor.

15. The method according to claim 4, wherein the settings selected on the microscope illumination unit are captured due to the spectral measurement of the illumination light emitted by the microscope illumination unit by means of a wavelength-sensitive sensor.

16. The method according to claim 5, wherein the settings selected on the microscope illumination unit are captured due to the spectral measurement of the illumination light emitted by the microscope illumination unit by means of a wavelength-sensitive sensor.

17. The method according to claim 6, wherein the settings selected on the microscope illumination unit are captured due to the spectral measurement of the illumination light emitted by the microscope illumination unit by means of a wavelength-sensitive sensor.

18. The method according to claim 7, wherein the settings selected on the microscope illumination unit are captured due to the spectral measurement of the illumination light emitted by the microscope illumination unit by means of a wavelength-sensitive sensor.

19. The method according to claim 8, wherein the settings selected on the microscope illumination unit are captured due to the spectral measurement of the illumination light emitted by the microscope illumination unit by means of a wavelength-sensitive sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Additional advantages, details, and further developments of the invention follow from the subsequent description of preferred embodiments of the invention, in reference to the drawing. The figures show as follows:

[0041] FIG. 1 is a representation of the principle of determining correction values according to a first preferred embodiment of the method according to the invention;

[0042] FIG. 2 is a representation of the principle of determining correction values according to a second preferred embodiment of the method according to the invention;

[0043] FIG. 3 is a flow chart of an identification of correction values according to the invention corresponding with a general embodiment;

[0044] FIG. 4 is a flow chart of the identification of correction values according to the invention corresponding with a typical embodiment; and

[0045] FIG. 5 is a flow chart of the identification of correction values according to the invention corresponding with a further typical embodiment.

DETAILED DESCRIPTION

[0046] FIG. 1 shows a representation of the principle of determining correction values according to a first preferred embodiment of the method according to the invention.

[0047] In a digital microscope, various settings and configurations can be adjusted. For instance, a dark field illumination or a bright field illumination may be selected, which is symbolized by a spectrum 01 of a dark field illumination and by way of a spectrum 02 of a bright field illumination, respectively. Furthermore, the spectral range can be adjusted, for instance in the visible wavelength range or in the near IR range, which may be caused, among other things, by a variation of the light source, such as a white light LED or a xenon lamp. Moreover, the spectral properties of transmission and/or reflection may be changed by the optical elements or by the optical system of the digital microscope. Furthermore, the spectral sensitivity of the image converter, in other words, of the sensor can be adjusted. The spectral properties of the optical system and of the image sensor are symbolized by spectra 03.

[0048] Each of the spectra 01, 02, 03 is described in the shown example by way of 200 respective grid points.

[0049] The method according to the invention uses a color reference 04 which may be physically available in the form of a color reference table, for instance and which is recorded with the digital microscope (cf. FIG. 2), or which is simulated as in the embodiment shown. For instance, N=24 reference colors may be used. In the case of the exemplary simulation shown, these N=24 colors are respectively shown as a spectrum with, for instance, M=200 grid points. Alternatively, also a reduced number may be selected, instance N=3 with M=3; for instance three values for RGB. The reference colors are symbolized by a first field 06.

[0050] The spectral properties 01, 02, 03 of the lighting, the optical system, and of the image sensor are symbolized by a second field 07. These spectral properties 01, 02, 03 determine how the uncorrected colors of the color reference 04 are shown, and therefore how they are falsified. It requires a color correction CC, which involves a white balance adjustment WB, in order to correct the falsified colors, which is symbolized by a third field 08. The result is the corrected colors 09 of the color reference, which is symbolized by a fourth field 11.

[0051] According to the invention, the correction values symbolized by the third parties field 08 are determined in order to then use them for the color correction of recorded images of samples.

[0052] Since the spectral properties 01, 02, 03 symbolized by the second field 07 of the lighting, the optical system, and of the sensor are known, in the embodiment shown, the correction values symbolized by the third field 08 can be determined mathematically in their entirety, which corresponds to a simulation of the digital microscope.

[0053] The identification of the correction values symbolized by the third field 08 may also be subdivided into two or multiple steps, if an interim step with interim reference data is needed. Such interim reference data may be defined by additional requirements in order to be able to fall back on different color spaces, such as CIE 1931 XYZ, for instance.

[0054] The fully mathematical identification of the correction values symbolized by the third field 08, taking into account the spectral properties 01, 02, 03 the lighting, the optical system and of the sensor, can be performed as a live solution, since while the examination under the microscope is performed, every adjustment of a spectral property, for instance by way of changes to the illumination level, leads to an entirely new calculation of the correction values. However, this embodiment may also be performed at a separate time, prior to the examination under the microscope, for which purposes the determined correction values must be stored in memory correspondingly. The calculation of the correction values may be performed by software, which may be operating, for instance, on a PC, on a tablet computer, or on a smartphone. The calculation of the correction values may also be performed by hardware, for instance by way of specific algorithms in a field programmable gate array (FPGA) or in a media processor.

[0055] FIG. 2 shows a representation of the principle of determining correction values according to a second preferred embodiment of the method according to the invention.

[0056] In this embodiment, the color reference 04 is physically used in the form of a color reference table, which is recorded with the digital microscope. Here too, N=24 reference colors are used, for example, so that N=24 RGB color values of the 24 recorded reference colors of the color reference table 04 are available. The recorded reference colors are the reference colors symbolized by the first field 06, which were impacted by the spectral properties 01, 02, 03 the lighting, the optical system and of the sensor, symbolized by the second field 07, which is symbolized by a joint field 06, 07.

[0057] The embodiment shown represents a calibration procedure in which the color reference table 04 is recorded with the digital microscope, and the settings of the digital microscope which determine the spectral properties 01, 02, 03 of the lighting, the optical system, and of the sensor provision are captured. As a result of varying settings, different spectral properties 01, 02, 03 are generated, in other words, different states of the digital microscope, with a set of correction values, in other words, a correction matrix, associated with each state. In addition, achromatic color references can be used for determining the correction values for the white balance adjustment.

[0058] The identification of the correction values can be done using the method of the least squares, in which an optimization for all reference colors is possible with identical weighting. Alternatively, the method of the least squares can be used while maintaining white color dots, in other words, an optimization is performed for all reference colors, in which the achromatic reference colors are weighted higher. Alternatively, other weightings can be performed.

[0059] Therefore, before the operation of the digital microscope, a plurality of sets of correction values is available, each of which is assigned to a respective state of the digital microscope. While the microscope is operated, it is possible to fall back to the previously determined sets of correction values; however, preferentially, a parameter-specific interpolation is performed, since the previously determined sets of correction values are only associated with a limited selection of possible states of the digital microscope. In a simple case, for instance, respective sets of illumination level correction values were determined in advance only for the two extremes: the minimum and the maximum illumination levels, respectively. In most cases, the illumination level setting on the digital microscope is between these two extremes, so that an interpolation must be performed between the correction values of the two previously determined sets.

[0060] The parameters representing the properties of the components of the digital microscope, such as the serial number, reference data, lighting, and spectrum, for instance, can be stored in different ways. A first possibility is the storage of these parameters on a PC, in a tablet computer or in a smartphone. Alternatively, these data can be stored at a central location. An additional preferred possibility is the storage of these parameters in the hardware of the respective components. The storage of the parameters representing the properties of the components of the digital microscope allows for specific color management algorithms for using the requisite parameters, if necessary. This makes it possible to guarantee a consistent color quality of the recorded images, independent of the respectively selected components. Different components such as different light sources for the microscope illumination unit or different interchangeable lenses, for instance, lead to entirely different properties, which is taken into account by a reading of the respective parameters and the use of these parameters. Different microscope illumination units can lead to entirely different spectra. For instance, spectra and color correction values of a dark field illumination source arranged in a lens can be stored in a memory element in the interchangeable lens. For instance, spectra and color correction values of a bright field illumination source can be stored together with spectral properties of the sensor in a memory element in the digital microscope.

[0061] FIG. 3 shows a flow chart of a correction value identification procedure according to a general embodiment of the method according to the invention. The calculations are performed on a PC, which constitutes an image processing unit of the digital microscope. To begin with, it is determined whether the required parameters or correction values are stored in the PC. If that is the case, the correction values for the color correction or the parameters, such as spectra, for instance, are read. They refer to a color family of the selected optical engine OE. The optical engine describes the optical recording by way of the digital microscope in its current state. Specifically, the optical engine describes the properties of the microscope illumination unit and of the image sensor. The color family is a selection of the possible colors. Furthermore, parameters of the selected lens are read from a lens database. The correction values for the color correction or the parameters are examined by way of a comparison with correction values and parameters stored in a memory arranged in the hardware components HW of the digital microscope. Then follows an approximation of the correction values, for instance by way of an interpolation of the read correction values. If the requisite parameters or correction values are not stored in the PC, they are calculated based on the parameters stored in the hardware components HW by way of a simulation.

[0062] FIG. 4 shows a flow chart of the correction value identification procedure according to a typical embodiment of the method according to the invention. Initially, the operational sequence is identical to the operational sequence shown in FIG. 1. In this case, however, it is assumed that not all required parameters are available. Correspondingly, there are queries as to whether the respective color families of the optical engine and of the lens are available. If they are not available, the respectively closest color family is used as a fall-back.

[0063] FIG. 5 shows a flow chart of the correction value identification procedure according to a further typical embodiment of the method according to the invention. Contrary to the processes shown in FIG. 1 and FIG. 3, a single color family D is exemplarily identified for the optical engine, and three color families A, B, F for the lens. The single color family D for the optical engine is exemplarily associated with a specific bright field illumination and with a specific sensitivity of the image sensor. Information about the color families and about the color correction values is stored in a database on the PC. These data are further stored in an EPROM memory in the components of the digital microscope. The required values are initially searched for on the PC. If they are not stored there, the values of the nearest color families are searched for. If these are not stored either, the required data are searched for in the memory arranged in the components of the digital microscope. If they are not stored even there, a state-identifying matrix is used, and a notification about the absent color correction values is returned.

[0064] As already explained above, the necessary color correction values can be obtained by way of interpolation. For these purposes, dependent on the actual parameters, different interpolation algorithms can be used.

[0065] For instance, interpolation may happen between two intensity values. In the event of an assumed linear interpolation between two parameters par.min and par.max, this results in the following equation for the i-th element CC.sub.r.sup.par . . . X of the color correction matrix or of the white balance matrix:

[00001]${\mathrm{CC}}_i^{\mathrm{par}..Math.X}={\mathrm{CC}}_i^{\mathrm{par}..Math.\min }+\mathrm{par}.X*\frac{{\mathrm{CC}}_i^{\mathrm{par}..Math.\max }-{\mathrm{CC}}_i^{\mathrm{par}..Math.\min }}{\mathrm{par}..Math.\max -\mathrm{par}..Math.\min }$

[0066] This equation can be expanded correspondingly for a higher order or for non-linear interpolation.

[0067] For instance, interpolation may happen between two types of illumination in a case of combined illumination. In the event of an assumed linear interpolation between an intensity of a bright field illumination I.sub.BF and an intensity of a dark field illumination I.sub.DF, this results in the following equation for the i-th element

CC.sub.I.sup.I.sup.DF.sup.I.sup.BF

of the color correction matrix or the white balance matrix:

CC.sub.I.sup.I.sup.DF.sup.I.sup.BF=a*CC.sub.I.sup.I.sup.DF+CC.sub.I.sup.I.sup.BF,

with

CC.sub.I.sup.I.sup.DF

and

CC.sub.I.sup.I.sup.BF

being the i-th element of the matrix of an exclusive dark field illumination or of an exclusive bright field illumination, and a being a normalization parameter for the absolute maximum intensity of the individual lightings, for instance a=I.sub.DF.max/I.sub.BF.max.

[0068] Furthermore, a combined interpolation between intensities and types of illumination can be performed as well.

[0069] As explained above, various properties of the digital microscope can be described by way of spectra. The spectral profiles be parameterized by way of a complex spectral curve with at least two Gaussian bell curves. This reduces the required amount of data reduced and allows for an increased flexibility for the interpolation of the color correction values between the various parameter-specific solutions. In this case, the interpolation is performed for the received values obtained by way of the parameterization of the spectra.

REFERENCE LIST

[0070] 01 Spectrum of a dark field illumination [0071] 02 Spectrum of a bright field illumination [0072] 03 Spectrum of an optical system and an image converter [0073] 04 Color reference values [0074] 05 — [0075] 06 Reference colors [0076] 07 Spectral properties of the optical system and of the sensor [0077] 08 Correction factors [0078] 09 Corrected colors [0079] 10 — [0080] 11 Corrected color values