Patent Description:
In the field of medical diagnostics, in many cases, one or more analytes have to be detected in samples of a body fluid, such as blood, interstitial fluid, urine, saliva or other types of body fluids. Examples of analytes to be detected are glucose, triglycerides, lactate, cholesterol or other types of analytes typically present in these body fluids. According to the concentration and/or the presence of the analyte, an appropriate treatment may be chosen, if necessary. Without narrowing the scope, the invention specifically may be described with respect to blood glucose measurements. It shall be noted, however, that the present invention may also be used for other types of analytical measurements using test strips.

Generally, devices and methods known to the skilled person make use of test strips comprising one or more test chemistries, which, in presence of the analyte to be detected, are capable of performing one or more detectable detection reactions, such as optically detectable detection reactions. With regard to these test chemistries, reference may be made e.g. to <NPL>. Other types of test chemistry are possible and may be used for performing the present invention.

Typically, one or more optically detectable changes in the test chemistry are monitored, in order to derive the concentration of the at least one analyte to be detected from these changes. For detecting the at least one change of optical properties of the test field of a test strip, various types of detectors (with various types of light sources for illuminating the test fields) are known (also referred to as dedicated meters or analytical measurement devices).

Further, besides using customized detectors, which are specifically developed for optically detecting changes in the test chemistry comprised by corresponding test strips, recent developments aim at using widely available devices such as smartphones. However, when consumer-electronics devices having a camera, such as smartphones, are employed instead of dedicated analytical measurement devices in order to determine analyte concentrations various influences need to be taken into account. As an example, lighting conditions, positioning, or other more or less uncontrollable conditions are to be considered.

To improve the reliability of a photometric analysis using a mobile device the <CIT> discloses a specimen test strip to detect a characteristic of an analyte in a specimen sample with an additional color calibration area besides a reaction area for receiving the specimen sample.

A method of analyzing a colorimetric assay to identify a value for an assay parameter is disclosed by <CIT> wherein intensity data for at least one of the color channels is converted to a first data point and compared with a standardized curve.

The <CIT> describes an auto white balance method wherein white balance settings are changed automatically to capture an aesthetically pleasing photograph, e.g. based on captured color values and/or a color emitted by a light source and/or on the subject of the photograph. Other auto white balance procedures are described in the <CIT> or the <CIT>.

<CIT> describes a method to select a white balance mode for achieving certain aesthetic effects, especially when capturing images at night, i.e. with no or low ambient light.

<CIT> describes an auto white balance procedure wherein an image is automatically segmented and different auto white balancing is applied to different segments.

<CIT> describes an initialization method for a camera comprising different preset capture settings such as automatic white balance. For initialization the camera enters a recursive process of capturing one or more image frames, starting with default automatic white balancing settings, analyzing the image frames by measuring the color balance of at least a portion of the captured image frame, which may include a blue/green color ratio and/or a red/green color ratio, against one or more thresholds, and adjusting the automatic white balance settings based on the analysis. The capturing, measuring and adjusting is repeated until the color balance of the image capture falls within an acceptable range.

A basic white balancing method for a digital camera device using a reference sample is described in <CIT>. The method comprises identifying the reference sample that is white in standard lighting conditions in a captured image, determining the correction factor based at least partially on the average color of the white reference sample and applying the correction factor to the captured image and/or a further captured image.

Despite the advantages involved in using a mobile device and a color reference card for performing an analytical measurement, several technical challenges remain. Specifically, the use of mobile devices to determine analyte concentrations using test strips may require an accurate determination of the color change of the test strip and, thus, often remains challenging. Appropriate image brightness and color balance needs to be ensured. The observed brightness and light color in the captured images, e.g., may be dependent on various influencing factors, such as settings determining the exposure or the white balance when capturing the image as well as post-processing steps applied to the image after it was captured.

The determination of some settings such, as exposure settings or white balancing settings, by the mobile devices are often a device-specific process conducted in an automatic mode. Typically, however, automatic white balance of mobile devices, such as mobile phones or tablets, aim at producing aesthetically pleasing images and not at reproducing colors as authentically as possible. Specially, the auto white-balancing settings automatically selected by a mobile device may lead to over-saturation and/or clipping in one or more of the color channels, which will prevent the further processing and determination of a blood glucose value on the basis of the respective image.

It is therefore desirable to provide methods and devices, which address the above-mentioned technical challenges of analytical measurements using mobile devices such as consumer-electronics mobile devices, specifically multipurpose mobile devices that are not dedicated to analytical measurements such as smartphones or tablet computers. Specifically, methods and devices shall be proposed which are widely applicable to available mobile devices and which are suited to increase measurement accuracy and convenience for the user.

This problem is addressed by the methods and devices with the features of the independent claims. Advantageous embodiments, which might be realized in an isolated fashion or in any arbitrary combinations, are listed in the dependent claims.

In the following, in most cases, when referring to the respective feature or element, the expressions "at least one" or "one or more" will not be repeated, notwithstanding the fact that the respective feature or element may be present once or more than once.

In a first aspect, a method of controlling auto white balance settings of a mobile device for performing a color based measurement using the mobile device and a color reference card is disclosed. The mobile device comprises a color camera and a plurality of preset white balance modes, each white balance mode associated with a different color temperature, and the color reference card comprises one or more gray fields each gray field having a known dedicated gray value.

The method may comprise further steps, which are not listed.

The term "controlling" generally refers to a process of influencing or regulating settings or a process for determining settings in a defined or definable fashion.

The term "auto white balance settings" as used herein is a broad term, is to be given its ordinary and customary meaning to a person of ordinary skill in the art, and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an automated process aiming to adapt camera settings to prevailing conditions, especially to a scene lighting, so that neutral colors like gray or white in a scene also appear neutral in an image captured by the camera. The term may further refer, without limitation, to an algorithm for selecting preset white balance settings with a correct color temperature to fit the scene lighting.

The term "color temperature" of light, e.g. from a light source or ambient light, as used herein is a broad term, is to be given its ordinary and customary meaning to a person of ordinary skill in the art, and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to the temperature of an ideal blackbody radiator that radiates light of a color comparable to the respective light.

The term "preset white balance mode" as used herein is a broad term, is to be given its ordinary and customary meaning to a person of ordinary skill in the art, and is not to be limited to a special or customized meaning. The term specifically may refer to a set of camera parameters for color balancing or chromatic adaptation to a specific color temperature, i.e. a specific light condition such as daylight or flashlight or other artificial or natural lighting. The camera parameters may relate, without limitation, to a scaling of the relative luminance by introducing relative scaling factors for different color channels of the camera. Examples for typical preset white balance modes, without limitation, are of the categories automatic, daylight, incandescent light, fluorescent light, cloudy, speed light, i.e. flash, and/or white balance preset.

The term "mobile device" as used herein is a broad term, is to be given its ordinary and customary meaning to a person of ordinary skill in the art, and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a mobile electronics device, more specifically to a mobile communication device such as a cell phone or a smartphone. Additionally or alternatively, as will be outlined in further detail below, the mobile device may also refer to a tablet computer or another type of portable computer having at least one color camera.

The term "color reference card" as used herein is a broad term, is to be given its ordinary and customary meaning to a person of ordinary skill in the art, and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an arbitrary item having, disposed therein or disposed thereon, such as on at least one surface, one or more gray fields having defined gray levels, i.e. gray values, and further, for example, a plurality of different color reference fields having known color properties or optical properties, such as having a plurality of colored fields having known reference color values. As an example, the color reference card may be a flat card comprising at least one substrate having, on at least one surface and/or disposed therein, the plurality of color reference fields having known color coordinates and one or more gray fields having known gray levels. The color reference card may also comprise one or more further gray fields. This will be described further below.

The substrate, specifically, may have a flat surface comprising one or more gray fields, and e.g. additionally a plurality of color reference fields and/or further gray fields. The substrate, as an example, may be or may comprise one or more of a paper substrate, a cardboard substrate, a plastic substrate, a ceramic substrate or a metal substrate. Laminate substrates are also possible. The substrate, as an example, may be sheet-like or flexible. It shall be noted, however, that the substrate may also be implemented into an article of use, such as into a wall of a box, a vile, a container, a medical consumable, such as a test strip, or the like. Thus, the color reference card may also fully or partially be integrated into a test strip. Thus, the at least one image of at least a part of the color reference card may fully or partially comprise an image of at least part of the test strip having at least one test field.

Further, the color reference card may comprise at least one position marker. The at least one position marker, as an example, may be or may comprise particularly an ArUco code or the like. Specifically, the at least one position marker may be arranged in at least one corner of the color reference card. Thus, the mobile device may be configured for detecting and/or reading the marker, specifically by optically detecting the marker (e.g., on the at least one image captured in step a)), and optionally retrieving information from the marker, such as information on the position and/or orientation of the color reference card in relation to the camera. The color reference card may include other marker(s) including further information or the position marker may additionally include further information. Such further information may include at least one of: an identifier for identifying the color reference card and/or the type of the color reference card, such as at least one of a label, a barcode or a QR-code; a specifier specifying details of the color reference card, such as reference color values, gray values and/or further gray background values or the like, such as by using at least one of a label, a barcode or a QR-code.

The term "gray field" as used herein is a broad term, is to be given its ordinary and customary meaning to a person of ordinary skill in the art, and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an arbitrary item having known optical properties, such as a known reference color value. Specifically, a gray field comprised by the color reference card may be a <NUM>-dimensional structure, such as a rectangle, a square, a polygon, a circle and/or an ellipse, with a uniform gray value, i.e. a dedicated gray value. The gray value of the gray field specifically may be one or more of predetermined, known or determinable. For example, gray values result when for r=g=b, i.e. a red, green and blue color value or color channel for an image point/pixel have equal values. The gray field may be comprised by a surface of the color reference card and/or disposed therein, specifically in such a way that at least part of the one or more gray fields may be visible in the image captured in step a).

The gray fields of the color reference card may be arranged in a regular pattern on the surface of the color reference card, such as in a rectangular pattern, e.g. a rectangular matrix pattern. The pattern arrangement specifically may enable identifying the gray fields, such as by searching at a predetermined distance in an x- and/or y-direction from one or more of the position markers.

Further, the one or more gray fields may be locally distributed over the color reference card, specifically over a part of the color reference card visible in the image.

The term "color camera" as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a device having at least one imaging element configured for recording or capturing spatially resolved one-dimensional, two-dimensional or even three-dimensional optical data or information. The camera may specifically comprise one or more imaging devices, such as camera chips or imaging chips, e.g. CCD and/or CMOS chips. The color camera, in particular the imaging device, may comprise a one-dimensional or two-dimensional array of image sensors, such as pixels. As an example, the color camera may comprise at least <NUM> pixels in at least one dimension, such as at least <NUM> pixels in each dimension. It shall be noted, however, that other cameras are also feasible. The color camera, besides at least one camera chip or imaging chip, may comprise further elements, such as one or more optical elements, e.g. one or more lenses. As an example, the camera may be a fix-focus camera, having at least one lens, which is fixedly adjusted with respect to the camera. Alternatively, however, the camera may also comprise one or more variable lenses that may be adjusted, automatically or manually. The camera may also comprise a diaphragm for controlling the aperture (whereby the amount of light that reaches the camera sensor may be controlled). The diaphragm functions much like the iris of the eye- it controls the effective diameter of the lens opening (called the aperture). The camera may further comprise an ambient light sensor for measuring light reflected by a scene to be captured in an image.

The invention specifically shall be applicable to cameras as usually used in mobile applications such as notebook computers, tablets or, specifically, cell phones such as smartphones. Thus, specifically, the color camera may be part of a mobile device which, besides the at least one camera, comprises one or more data processing devices such as one or more data processors. Other color cameras, however, are feasible.

For each pixel of the color camera, color information may be provided or generated, such as color values for three colors R, G, B. A larger number of color values is also feasible, such as four color values for each pixel, for example R, G, G, B. Color cameras are generally known to the skilled person. Thus, as an example, the camera chip may consist of a plurality of three or more different color sensors each, such as color recording pixels like one pixel for red (R), one pixel for green (G) and one pixel for blue (B). For each of the pixels, such as for R, G, B, values may be recorded by the pixels, such as digital values in the range of <NUM> to <NUM>, depending on the intensity of the respective color. Instead of using color triples such as R, G, B, as an example, quadruples may be used, such as R, G, G, B. The color sensitivities of the pixels may be generated by color filters or by appropriate intrinsic sensitivities of the sensor elements used in the camera pixels. For example, gain can be a digital camera setting that controls the amplification of the signal from the camera sensor.

The term "image" as used herein is a broad term, is to be given its ordinary and customary meaning to a person of ordinary skill in the art, and is not to be limited to a special or customized meaning. The term may specifically refer, without limitation, to a set of spatially resolved optical data. Specifically, the term may relate to data recorded by using a camera, such as a plurality of electronic readings from the imaging device, such as the pixels of the camera chip. Further, the term may refer, without limitation, to a color digital image made of pixels, each pixel comprising color information for at least three different colors, i.e. at least three different wavelengths of light. For example, each pixel is made of a combination of color values, especially for different primary colors such as red, green and blue. In an embodiment the image may comprise a plurality of color pixels, each color pixel comprising an n-tuple of at least three color values for three different colors. In an alternative embodiment, the image may further comprise at least three different color channels, wherein a color channel may refer to a grayscale image, of the same size as the image, made of just one of the at least three colors.

The term "capturing an image" as used herein is a broad term, is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to one or more of imaging, image recording, image acquisition, image capturing. The term "capturing an image" may comprise capturing at least one single image, i.e. one image and/or a plurality of images such as a sequence of images. For example, the capturing of the image may comprise recording continuously a sequence of images such as a video or a movie. The capturing of the image may be initiated by user action or may automatically be initiated, e.g. once the presence of the at least one object within a field of view and/or within a predetermined part of the field of view of the camera is automatically detected. These automatic image acquisition techniques are known e.g. in the field of automatic barcode readers, such as from automatic barcode reading apps. The capturing of the images may take place, as an example, by acquiring a stream or "live stream" of images with the camera, wherein one or more of the images, automatically or by user interaction such as pushing a button, are stored and one of them is used as the at least one image. The image acquisition may be supported by a processor of the mobile device, and the storing of the images may take place in a data storage device of the mobile device.

The capturing of the image of at least part of the one or more gray fields of the color reference card by using the color camera may imply taking an image which at least comprises a region of interest within the at least one gray field. Thus, as an example, one or more gray fields may be detected automatically within the image, e.g. by pattern recognition techniques generally known to the skilled person, and at least one region of interest may be chosen within each gray field, e.g. a rectangular, square, polygonal, oval or round region of interest. The taking of the image may be initiated by the user action or may automatically be initiated once the presence of the at least one gray field within a field of view and/or within a predetermined sector of the field of view of the camera is automatically detected.

The term "region of interest" as used herein is a broad term, is to be given its ordinary and customary meaning to a person of ordinary skill in the art, and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a selected portion of the image, said portion comprising one or more areas within the image or the whole image. The region of interest may be determined by selecting an area within the image, e.g. automatically determining and selecting an area within the image comprising at least one gray field. The area or portion of the image may refer to a corresponding part of the pixels, e.g. color pixels, of the image and/or a corresponding part of each of the color channels of the image.

The terms "overexposed" and "overexposure" as used herein are a broad term. The terms specifically may refer, without limitation, to an amount of light per unit area or the amount of light of a certain wavelength or range of wavelength exceeding a preset threshold or exceeding the amount that can be reliably captured, e.g. when the intensity in an image area falls outside the maximum intensity, which can be represented. Alternatively and without limitation, the term may refer to a guide value, such as an average value or a median or a maximum, determined for the region of interest said guide value exceeding a preset threshold.

Thus the "determining for a region of interest within the image a number of gray fields for which the color information for a certain color shows overexposure" may refer without limitation to determining for the region of interest within the image a number of gray fields for which the color information for a certain color exceeds a preset threshold.

"Overexposure of the color information for a certain color for the region of interest" may refer, without limitation, to the color information for the region of interest exceeding a preset threshold or corresponding to a maximum. Alternatively and without limitation, it may refer to one, more or all pixels within the region of interest exceeding a preset threshold or corresponding to a preset maximum value. In another alternative, without limitation, it may refer to a guide value exceeding a preset threshold or corresponding to a preset maximum, the guide value being determined for the region of interest. The guide value, without limitation, may refer to an average, a median or a maximum determined for the respective pixels. Furthermore, the guide value, without limitation, may be determined on the bases of one, more or all pixels of the region of interest.

According to steps d) and e) the method jumps back to step a) and a new image is captured, i.e. the image is re-captured, if the first and/or second overexposure-number or a sum of the first and second overexposure-number exceeds a preset respective overexposure-threshold. This may imply, that either one overexposure-number or both overexposure-numbers or the sum or a combination of the aforementioned values is compared to a preset appropriate threshold and that a re-capturing is performed if one or if all of the values compared to a threshold exceed the respective threshold. The value of either of the overexposure-numbers or a sum of both relates to a degree of overexposure in the image.

For the re-capturing of the image, a new white balance mode is selected based on an analysis of the determined overexposure-numbers. If the first overexposure-number is greater than the second overexposure-number, i.e. the overexposure for light with a smaller wavelength, i.e. cooler color temperature, exceeds the overexposure for greater, warmer wavelengths a white balance mode associated with a warmer color temperature, i.e. a warmer white balance mode is selected. Correspondingly, if a greater overexposure is determined for greater, warmer wavelength, i.e. the second color, a white balance mode associated with a cooler color temperature (cooler white balance mode) is selected. For example, the next cooler or warmer white balance mode is selected, respectively. Alternatively, any one of the cooler or warmer white balance modes is selected. According to an embodiment, a difference between the two overexposure-numbers is determined and the warmer or cooler white balance mode is selected on the basis of the determined difference.

An advantage of the described method is, that on the bases of the preset device conditions, i.e. the preset white balance modes available for the device, the best mode is selected in a directed recursive process. Therefore, the described method is particularly easy and fast and helps to increase the reliability of a color measurement via a mobile device.

In the described recursive process the preset white balance modes may be selected following preset order, e.g. the next warmer or colder mode is selected or the next but one warmer or colder mode is selected or any one of the warmer or colder modes is selected.

Furthermore, it is understood that the recursive process may end at any reasonable break point. A break condition may, for example, be the fact that all preset white balance modes have been used or that the first and second overexposure-number are equal or that the difference between the first and second overexposure-number has reached a minimum or that said difference starts growing again.

According to an embodiment, the method steps b) and c) comprise identifying at least a portion of the color information for the respective color corresponding to the gray fields within the region of interest, determining a guide value for the identified portion of the color information and determining whether the guide value exceeds a predetermined overexposure-threshold.

The identifying may refer to finding all or a portion, e.g. based on predefined conditions, of the pixels and/or color information corresponding to the gray fields. For example, a plurality of color pixels or of pixels of a color channel and the corresponding respective values for the color are identified.

The term "guide value" as used herein is a broad term, is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an average value, a median, and/or a maximum value determined for the identified color information, e.g. the plurality of values for the specific color of the identified color pixels or the plurality values of the identified pixels of the specific color channel.

According to another embodiment, the second color is red and the first color is blue or green. Preferably, the first color is blue as in this case the difference between the corresponding wavelength of the first and second color is bigger than for the first color being green.

According to a further embodiment, the color based measurement is an analyte measurement based on a color formation reaction, wherein the color formation reaction occurs in a test strip having a sample applied to a test field of the test strip.

The term "color formation reaction" as used herein is a broad term, is to be given its ordinary and customary meaning to a person of ordinary skill in the art, and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a chemical, biological or physical reaction during which a color, specifically a reflectance, of at least one element involved in the reaction, changes with the progress of the reaction. Thus, as an example, reference may be made to the above-mentioned biochemical reactions, which typically are used for detecting blood glucose, involving a color change. Other types of color changing or color formation reactions are known to the skilled person, such as typical chemical reactions for determining the pH value.

The term "test strip" as used herein is a broad term, is to be given its ordinary and customary meaning to a person of ordinary skill in the art, and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a strip shaped element or device configured for performing a color-change detection reaction. The test strip may also just be referred to as test strip herein, wherein these terms may refer to the same element. The test strip may particularly have a test field, e.g. containing at least one test chemical for detecting at least one analyte. The test strip, as an example, may comprise at least one substrate, such as at least one carrier, with the at least one test field applied thereto or integrated therein. In particular, the test strip may further comprise at least one white area, such as a white field, specifically in a proximity to the test field, for example enclosing or surrounding the test field. The white area may be a separate field independently arranged on the substrate or carrier. However, additionally or alternatively, the substrate or carrier itself may be or may comprise the white area. The at least one carrier may be strip-shaped, thereby providing the basic form of the test strip. These test strips are generally widely in use and available. One test strip may carry a single test field or a plurality of test fields having identical or different test chemicals comprised therein.

As further used herein, the term "test field" is a broad term, is to be given its ordinary and customary meaning to a person of ordinary skill in the art, and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a coherent amount of the test chemical, such as to a field or a region, e.g. a field of round, polygonal or rectangular shape, having one or more layers of material, with at least one layer of the test field having the test chemical comprised therein.

The test strip may be placed on top of the color reference card, and/or the color reference card may comprise one or more windows, wherein the color reference card, with the one or more windows, is placed on top of the test strip such that the test field or at least a part of the test field is visible through the window.

According to another embodiment, the color reference card further comprises a plurality of different color reference fields having known reference color values.

The term "color reference field" as used herein is a broad term, is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an arbitrary item having known optical properties, such as a known reference color value. Specifically, a color reference field comprised by the color reference card may be a <NUM>-dimensional structure, such as a rectangle, a square, a polygon, a circle and/or an ellipse, with a uniform color value. The color value of the color reference field specifically may be one or more of predetermined, known or determinable. The color reference field may be comprised by a surface of the color reference card and/or disposed therein, specifically in such a way that at least part of the plurality of different color reference fields (e.g. one color reference field) may be visible in the image captured in step c).

Further, the color reference fields may have color values in a subspace of the color coordinate system corresponding to the color space of the color formation reaction of the reagent test region. The color reference fields of the color reference card specifically may be arranged in a regular pattern on the surface of the color reference card, such as in a rectangular pattern, e.g. a rectangular matrix pattern. The pattern arrangement specifically may enable identifying the color reference fields, such as by searching at a predetermined distance in an x- and/or y-direction from one or more of the position markers.

According to a further embodiment, the image captured in step a) additionally captures at least part of the test field of the test strip. This helps to ensure that the captured image may be used to perform a color based measurement, e.g. to determine an analyte concentration. Therewith, a further step of capturing an image for the color-based measurement is not necessary.

According to another embodiment, the method further comprises determining a concentration of the analyte in the sample by using the image captured in step a), if a sum of the first overexposure-number and the second overexposure-number is smaller than the preset overall overexposure-threshold and/or if a difference between the first overexposure-number and the second overexposure-number is smaller than a preset balance threshold. Alternatively, a further image is captured and used for determining a concentration of the analyte in the sample if the aforementioned conditions are fulfilled.

According to a further embodiment, steps a) to e) are iterated until a difference between the first overexposure-number and the second overexposure-number is smaller than a preset balance threshold, or until step a) has been performed for all white balancing modes of the plurality of white balancing modes, or until a difference between the first overexposure-number and the second overexposure-number starts increasing compared to a difference determined based on a previously captured image, and then a concentration of the analyte in the sample is determined using the image corresponding to the smallest difference between the first overexposure-number and the second overexposure-number, or using an extra image captured using the auto white balancing mode corresponding to the smallest difference between the first overexposure-number and the second overexposure-number.

According to another embodiment, the mobile device comprises a display, and the method further comprises the step of providing visual guidance on the display for positioning the camera relative to a scene, the scene comprising at least part of the test strip and/or at least part of the color reference card. The visual guidance, e.g., comprises one or more arrows, frames or lines indicating a preferred positioning of the camera relative to the object. As one example, the visual guidance comprises an outline, which corresponds to the shape of the object superimposed on the display of the mobile device.

Providing visual guidance on the display for positioning the camera relative to an object on the display for determining the exposure parameters and/or for capturing the at least one image may in particular relate to providing visual guidance on the display in order to guide the user to position the camera such that the scene comprises at least part of the one or more gray fields of the color reference card. The guidance may additionally provide visual guidance to guide the user to position the camera such that the scene additionally comprises further structures such as at least part of the test field of the test strip having the sample applied thereto and/or at least part of the plurality of different color reference fields of the color reference card. The visual guidance, e.g., may comprise an outline, which corresponds to the shape of at least part of the color reference card and/or at least part of the test strip superimposed on the display of the mobile device.

According to a further embodiment, the color reference card comprises at least one position marker.

According to another embodiment the method is initiated automatically in case it is determined that the camera is in a defined position with respect to the color reference card based on the at least one position marker.

According to a further embodiment, the test field is in a defined position with respect to the color reference card during capturing the at least one image.

According to a further aspect of the invention a mobile device is disclosed having at least one camera and at least one display, the mobile device being configured for performing the method as described above.

According to another aspect of the invention a kit for determining the concentration of an analyte in a bodily fluid is disclosed, the kit comprising the above-described mobile device, at least one test strip having at least one test field, at least one color reference card, wherein the color reference card comprises a plurality of different color reference fields having known reference color values and one or more gray fields having a defined gray value.

According to a further aspect of the invention a computer program comprising instructions which, when the program is executed by a mobile device having a camera, cause the mobile device to carry out at least steps a) to d) of the methods as described above.

According to another aspect of the invention a computer-readable storage medium is disclosed, specifically a non-transitory storage medium, comprising instructions which, when executed by a mobile device having a camera, cause the mobile device to carry out at least steps a) to e) of the method as described above.

In <FIG>, an exemplary embodiment of a color reference card <NUM> is shown in a plan view. The color reference card <NUM> comprises one or more gray fields <NUM> having known gray values as well as a plurality of color reference fields <NUM> having known reference color values. The gray fields <NUM> and the color reference fields <NUM> may be arranged on the surface of the color reference card <NUM>, such as on a substrate of the color reference card <NUM>.

The color reference fields <NUM> may be distributed equally over the surface of the color reference card <NUM>, specifically in such a way that the plurality of color reference fields 112may be distributed over the entire surface of the color reference card <NUM>. As an example, the color reference fields <NUM> may be arranged in matrix pattern, such as a rectangular matrix pattern. However, the color reference fields <NUM> may also be arranged in other ways.

The one or more gray fields <NUM> may be surrounding the color reference fields <NUM> and/or framing the color reference card and/or be distributed along rows and/or columns between the color reference fields <NUM> matrix pattern. The color reference fields <NUM> and the gray fields <NUM> may not overlap each other.

The color reference card <NUM> may further comprise at least one window <NUM>. Thus, at least one test strip <NUM> or a part thereof may be visible through the window <NUM> when the color reference card <NUM> is placed on top of the test strip <NUM>. Specifically, at least one test field <NUM> comprised by the test strip <NUM> may be visible through the window <NUM> of the color reference card <NUM>. As another example, the color reference card <NUM> may comprise the test strip <NUM> having at least one test field <NUM>, specifically in such a way that the at least one test field <NUM> is accessible and visible.

Further, the color reference card <NUM> may comprise at least one position marker <NUM>. The position marker <NUM> may particularly be an ArUco code. In <FIG>, the position marker <NUM> specifically may comprise one or more ArUco codes, such as in the corners of a rectangular matrix comprising the color reference fields <NUM> and some of the gray field <NUM> and being surrounded by a gray field <NUM>. Thus, generally, the position marker <NUM> may be arranged in at least one corner <NUM> of the color reference card <NUM>. For example, at least one position marker <NUM> may be arranged in each of the corners <NUM> of the color reference card <NUM>, specifically in such a way that the position marker <NUM> may be visible together with the plurality of color reference fields <NUM>. Further, the position marker <NUM> may comprise information about the orientation of the color reference card <NUM>.

In <FIG>, an exemplary embodiment of a kit is shown in a perspective view. The kit comprises at least one mobile device <NUM> and at least one color reference card <NUM>. Further, the kit comprises the at least one test strip <NUM>.

The mobile device <NUM> may be or may comprise at least one of a cell phone, a smartphone, a tablet computer or the like. Further, the mobile device <NUM> has at least one color camera <NUM>. The color camera <NUM> of the mobile device <NUM> may be configured for recording images, specifically color images. For example, the color camera <NUM> comprises at least three color sensor types, such as at least one color sensor type for red, green and blue, respectively.

Further, the mobile device <NUM> may comprise at least one processor <NUM>. The processor132 may be configured, specifically by software programming, to perform one or more of the method steps a) to d) of the method of controlling auto white balance settings. Exemplary embodiments of the above-mentioned methods are shown in <FIG> and will be described in further detail below. Thus, reference may be made to the description of <FIG>.

The processor <NUM> may specifically be configured for supporting the setting of a region of interest and determining a first and second overexposure-number for the gray fields in the region of interest. The processor <NUM> may further specifically be configured for capturing at least one image comprising a scene <NUM>. In the embodiment shown, the scene <NUM> comprises the entire color reference card <NUM> and the test field <NUM> of the test strip <NUM>. Specifically, the processor <NUM> may prompt a user of the mobile device <NUM> to capture the image. Additionally or alternatively, the processor <NUM> may be configured for automatically capturing the image of the color reference card <NUM>, specifically when the color reference card <NUM> may be in a field of view of the camera <NUM>.

The color reference card <NUM> has been described above (see <FIG>).

The at least one marker <NUM> of the color reference card <NUM> may be used for identifying the color reference card <NUM>. Specifically, the processor <NUM> of the mobile device <NUM> may be configured for detecting the position marker <NUM> in a field of view of the color camera <NUM>.

The color reference card <NUM> and the test strip <NUM>, may be visible on the at least one image captured by the color camera <NUM> of the mobile device <NUM>. Specifically, the at least one test region <NUM> of the test strip <NUM> may be visible through the window <NUM> of the color reference card <NUM>.

<FIG> shows the situation when capturing the image. Visual guidance is provided in this embodiment on the display in form of an outline <NUM> of the color reference card superimposed on the display <NUM> of the mobile device <NUM> in order to guide the user to position the camera such that the captured scene <NUM> which corresponds to the outline <NUM> comprises at least part of one or more gray fields. In the example shown, the scene in the set exposure metering area comprises the entire color reference card.

Controlling the auto white balance settings and capturing the image may be initiated automatically. The capturing of an image may, e.g., be initiated automatically in case it is detected that, based on the position marker <NUM>, the color reference card is within field of view of the camera <NUM>.

<FIG> shows a flow chart of an exemplary embodiment of a method of controlling auto-exposure settings of a mobile device <NUM>.

The method is executed by the processor and/or other processing means and starts with acquiring using the camera <NUM> and one of the white balance modes an image of at least part of the one or more gray fields <NUM> of the color reference card <NUM>, the image comprising a plurality of pixels and color information for at least three different colors for the plurality of pixels, and wherein in the shown embodiment the color reference card is detected in the image based on the ArUco codes;.

For at least one region of interest ROI within the image a number of gray fields <NUM> for which the color information for a first color, channel B, shows overexposure is determined as a first overexposure-number. Correspondingly, for the same regions of interest ROI within the image a number of gray fields <NUM> for which the color information for a second color, channel R, shows overexposure is determined as a second overexposure-number, wherein the first color, here blue, relates to a smaller wavelength or a range of smaller wavelength than the second color, here red;.

It is determined whether the sum of the first and second overexposure-numbers exceeds a threshold N and in case of no exaggerated overexposure, i.e. the sum of first and second overexposure-numbers not exceeding the threshold N, the color based measurement is performed with current image or a newly captured image using the current white balance mode.

In case of an exaggerated overexposure, i.e. the sum of first and second overexposure-numbers exceeding the threshold N, the first overexposure-number for channel B and the second overexposure-number for channel R are compared.

If the first overexposure-number for B is larger than the second overexposure-number for R in the shown embodiment it is checked whether the used white balance mode already has been the warmest and if this is the case the color based measurement is performed with current image or a newly captured image using the current white balance mode. If the used white balance mode is not the warmest a white balance mode associated with a warmer color temperature is selected from the plurality of white balance modes and the described process is started again acquiring an image using the newly selected white balance mode.

If the first overexposure-number for B is not larger than the second overexposure-number for R in the shown embodiment it is checked whether the used white balance mode already has been the coolest and if this is the case the color based measurement is performed with current image or a newly captured image using the current white balance mode. If the used white balance mode is not the coolest a white balance mode associated with a cooler color temperature is selected from the plurality of white balance modes and the described process is started again acquiring an image using the newly selected white balance mode.

Claim 1:
A method of controlling auto white balance settings of a mobile device (<NUM>) for performing a color based measurement using the mobile device (<NUM>) and a color reference card (<NUM>),
- wherein the mobile device (<NUM>) comprises at least one processor (<NUM>), a color camera (<NUM>) and a plurality of preset white balance modes, each white balance mode associated with a different color temperature, and
- wherein the color reference card (<NUM>) comprises gray fields (<NUM>) each gray field having a known dedicated gray value,
the method comprising:
a. Capturing, supported by the at least one processor (<NUM>), using the camera (<NUM>) and one of the white balance modes an image of at least part of the gray fields (<NUM>) of the color reference card (<NUM>),
i. the image comprising a plurality of pixels and color information for at least three different colors for the plurality of pixels, each color corresponding to a wavelength of light,
characterized in that the method further comprises:
b. determining, by the processor (<NUM>), for a region of interest within the image a number of gray fields (<NUM>) for which the color information for a first color shows overexposure by exceeding a preset threshold as a first overexposure-number,
c. determining, by the processor (<NUM>), for the region of interest within the image a number of gray fields (<NUM>) for which the color information for a second color shows overexposure by exceeding a preset threshold as a second overexposure-number
i. wherein the first color relates to a smaller wavelength or a range of smaller wavelength than the second color,
d. re-capturing, supported by the processor (<NUM>), the image of step a) with a white balance mode associated with a warmer color temperature if one of the first and second overexposure-numbers or a sum of the first and second overexposure-numbers exceeds a respective preset overexposure-threshold, and the first overexposure number is greater than the second overexposure number,
e. re-capturing, supported by the processor (<NUM>), the image of step a) with a white balance mode associated with a cooler color temperature if one of the first and second overexposure-numbers or a sum of the first and second overexposure-numbers exceeds a respective preset overexposure-threshold, and the first overexposure number is smaller than the second overexposure number.