METHOD FOR EVALUATING AN INFRARED SIGNATURE

Abstract

A method for evaluating an infrared signature present on an object surface, which signature preferably forms a two-dimensional code. Furthermore, a monochrome or multicolour pattern, which reflects light in the visible wavelength range, can be present on the object surface. The infrared signature only absorbs light in the infrared range and can consequently be detected by means of an IR camera. In the method, an infrared light source is switched on and the infrared signature is illuminated with infrared light and an original image is recorded with an infrared camera in this state. The original image or a further-processed image based thereon is then filtered by a high-pass filter, the contrast in the image being increased indirectly or directly after the high-pass filtering. The infrared signature can finally be evaluated in the image processed in this way.

Claims

1. A method for evaluation of an infrared signature applied on an object surface comprising the following steps: switching on an infrared light source and illuminating the infrared signature with infrared light; capturing of an initial image by means of an infrared camera; creating a high-pass filtered image based on the initial image by means of high-pass filtering in order to mitigate or eliminate an infrared light spot that is present in the initial image on the infrared signature; creation of a high-contrast image by increasing a contrast in an image based on the high-pass filtered image; and evaluating the infrared signature in an image based on the high-contrast image.

2. The method according to claim 1, wherein in addition at least one color and/or a pattern in the a visible spectral range is present on the object surface.

3. The method according to claim 1, wherein the infrared camera is configured to image light in a non-visible infrared spectral range and in the visible spectral range.

4. The method according to claim 3, wherein prior to entry in the infrared camera light is filtered by means of an input filter that is configured to allow light in the non-visible infrared spectral range to pass and to reduce or eliminate light in the visible spectral range.

5. The method according to claim 1, wherein the infrared camera is configured to image light in a non-visible infrared spectral range up to a wavelength of maximum 50 μm or maximum 20 μm or maximum 10 μm or maximum 3-5 μm.

6. The method according to claim 1, wherein the infrared light source continuously emits infrared light during capturing of the initial image.

7. The method according to claim 1, wherein a blurred image is created by blurring of the initial image.

8. The method according to claim 7, wherein the high-pass filtering is carried out in that a difference image is created from the initial image and the blurred image.

9. The method according to claim 1, wherein a blurred image is created by blurring of a high-pass filtered image.

10. The method according to claim 1, wherein a blurred image is created by blurring of the high-contrast image.

11. The method according to claim 6, wherein the blurring is carried out by means of a low-pass filter or a Gaussian filter or a Fourier transformation.

12. The method according to claim 1, wherein the high-pass filtering is carried out by means of a high-pass filter or a Fourier transformation.

13. The method according to claim 1, wherein the infrared signature is a two-dimensional code and evaluation of the infrared signature is carried out based on an application program to which the high-contrast image or an image based on the high-contrast image is transmitted.

14. Use of a mobile device comprising a processor that is communicatively connected with an infrared camera and an infrared illumination for carrying out the method according to claim 1.

15. Use of the mobile device according to claim 14, wherein the mobile device comprises an infrared camera and an infrared illumination installed in a housing of the mobile device.

16. Use of the mobile device according to claim 14, wherein the mobile device comprises at least one or exactly one external unit outside a housing of the mobile device having an infrared camera and an infrared illumination, wherein the external unit is communicatively connected with the processor in a wireless or wired manner.

17. The method according to claim 2, wherein the infrared camera is configured to image light in a non-visible infrared spectral range and in the visible spectral range.

18. The method according to claim 17, wherein prior to entry in the infrared camera light is filtered by means of an input filter that is configured to allow light in the non-visible infrared spectral range to pass and to reduce or eliminate light in the visible spectral range.

19. The method according to claim 18, wherein the infrared camera is configured to image light in a non-visible infrared spectral range up to a wavelength of maximum 50 μm or maximum 20 μm or maximum 10 μm or maximum 3-5 μm.

20. The method according to claim 19, wherein the infrared light source continuously emits infrared light during capturing of the initial image.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Advantageous embodiments of the invention are obtained from the dependent claims, the description and the drawings. In the following, preferred embodiments of the invention are described in detail based on the attached drawings. The drawings show:

[0032] FIG. 1 a highly schematic illustration of a mobile device having an infrared camera and an infrared illumination,

[0033] FIG. 2 an object surface having a pattern and a schematically illustrated infrared signature,

[0034] FIG. 3 a block-diagram-like illustration of the mobile device of FIG. 1 during the capturing of an initial image of the object surface of FIG. 2,

[0035] FIG. 4 a flow diagram of an embodiment of an inventive method,

[0036] FIG. 5 a schematic illustration of a high-pass filter in the form of a difference filter,

[0037] FIG. 6 a schematic illustration of a low-pass filter in the form of a difference filter,

[0038] FIG. 7 a block-diagram-like illustration for realization of a high-pass filtering of an initial image and a blurred image,

[0039] FIG. 8 an exemplary illustration of an initial image, wherein the infrared signature is surrounded by dashed lines in the initial image,

[0040] FIG. 9 an exemplary illustration of a high-pass filtered image, wherein the infrared signature in the high-pass filtered image is surrounded by dashed lines,

[0041] FIG. 10 an exemplary illustration of a high contrast image after increasing the contrast in the high-pass filtered image according to FIG. 9 and

[0042] FIG. 11 an exemplary illustration of a blurred image that was obtained from the high contrast image by blurring and serves as result image for the evaluation of the infrared signature.

DETAILED DESCRIPTION

[0043] A mobile device 15 is schematically illustrated in FIGS. 1 and 2 that can be formed by a mobile phone or smartphone or a tablet personal computer for example. The mobile device 15 has an integrated infrared camera 16 as well as an integrated infrared light source 17 according to the example. The infrared light source 17 can be formed by an infrared LED. The infrared light source 17 is asymmetrically configured or arranged relative to the optical axis of the infrared camera 16. The mobile device 15 can comprise in addition a common camera 18 for visible light as well as a light source 19 for visible light. The light source 19 serves as flash for illumination during capturing of images with the camera 18.

[0044] Preferably, one single infrared light source 17, e.g. one single infrared light emitting diode is provided.

[0045] The infrared camera 16 and the infrared light source 17 are communicatively connected with a processor 20 of the mobile device 15. The processor 20 can be configured to execute programs and applications of the mobile device 15, particularly an application for evaluation of a two-dimensional code, such as a QR-code, a bar code or a data matrix code. The communication connection between the processor 20 and the infrared camera 16 and the infrared light source 17 can be established in a wireless and/or wired manner.

[0046] The infrared camera 16 and the infrared light source 17 are arranged in a housing of the mobile device 15 according to the example. In another embodiment the processor 20 can have a communication interface to which the infrared camera 16 and the infrared light source 17 can be connected. In this case, the infrared camera 16 and/or the infrared light source 17 can be arranged as external units outside of the housing of the mobile device 15 in which the processor 20 is arranged. For example, an external infrared camera 16 and an external infrared illumination 17 can form a unit that can be commonly connected to an interface on or in the housing of the mobile device 15. In doing so, the at least one external unit can communicate with the processor 20 arranged in the housing of the mobile device 15.

[0047] The infrared camera 16 is configured to detect light in the visible spectral range and in the non-visible infrared range and to image it in a captured image. Infrared cameras 16 that can also capture light in the visible spectral range are frequently seen in standard devices, because it is in fact desired to capture not only light in the infrared range, but—as far as present—also residual light that is still present in the visible range in order to optimally use the available light conditions for the initial image. For example, the infrared camera 16 can be configured to capture and image light in the IR-A range of 780 nm to approx. 1.4 μm. In addition or as an alternative, the infrared camera 16 can also be configured to image light in the spectral range with a wavelength of approximately 1.4 μm to 3.0 μm (IR-B). Preferably, the infrared camera 16 is configured to image light in the spectral range with wavelengths of maximum 50 μm or maximum 20 μm or maximum 10 μm or maximum 3-5 μm.

[0048] The mobile device 15 serves for detection and evaluation of an infrared signature 25 that is particularly apparent in FIGS. 2, 10 and 11. The infrared signature 25 forms a two-dimensional code, e.g. a Quick Response code (QR-code), a bar code or the like. Such a code contains encrypted or coded information by means of graphical elements that can be read by means of the mobile device 15.

[0049] The infrared signature 25 is applied on an object surface 26 of an object 27, particularly printed. The infrared signature 25 is not visible for the human eye during radiation with light in the visible wavelength range. The infrared signature 25 absorbs preferably light in the wavelength range of at least 780 nm. This IR-absorption can be detected by means of an IR-camera. Additional illustrations, patterns, images, forms, symbols or the like in one or multiple colors in the visible spectral range can be illustrated on the object surface 26 of the object 27 beside the infrared signature 25. Only by way of example, schematic patterns in form of suns, moons and stars are illustrated in FIG. 2. As apparent from FIG. 2, the infrared signature 25 and the pattern 28 overlap on the object surface 26.

[0050] Because the infrared camera 16 is configured to capture and image light in the wavelength range of the visible light as well as the non-visible infrared range, the detection and evaluation of the infrared signature 25 is affected by the pattern 28. In order to counteract to this, an input filter 29 is present. The input filter 29 is placed on or over the objective lens of the infrared camera 16 and can be formed, for example, by means of a foil. The input filter 29 is thus located in the light path between the object surface 26 having the infrared signature 25 and the infrared camera 16. The input filter 29 is configured to allow light in the non-visible infrared range having a wavelength of at least 780 nm to pass through and to block the light with wavelengths smaller than 780 nm as far as possible completely. In doing so, it is avoided that the pattern 28 affects the detection and evaluation of the infrared signature 25, but to allow that a simple and inexpensive infrared camera can be used that also images light in the visible wavelength range.

[0051] By means of the mobile device 15, a method is executed for detection and evaluation of the infrared signature 25, an embodiment of which is illustrated in the flow diagram of FIG. 4.

[0052] In a first method step S1 the infrared light source 17 is switched on. In the switched on condition the infrared light source 17 continuously emits infrared light L. By emission of the infrared light L on the object surface 26, an area illuminated with infrared light L is created that can also be denoted at infrared light spot 30. The infrared light spot 30 is illustrated in FIG. 8 by an elliptical bright area. The infrared light spot 30 preferably illuminates an area on the object surface 26 that is larger than the infrared signature 25 that is located within the infrared light spot 30 (FIG. 8).

[0053] In a second method step S2 an initial image 31 is captured by means of the infrared camera 16. An embodiment of the initial image 31 is illustrated in FIG. 8. During the capturing of the initial image 31, i.e. during the entire exposure time of the infrared camera 16, the infrared light source 17 remains continuously switched on. Preferably, the intensity of the infrared light L emitted by the infrared light source 17 is constant during the entire capturing of the initial image 31.

[0054] As it can be seen based on the exemplary initial image 31 of FIG. 8, the infrared signature 25 shown in the initial image 31 is outshined by the infrared light spot 30 and is hardly or not recognizable. For this reason and for sake of clarity a dashed frame was inserted in FIG. 8 within which the captured infrared signature 25 is located.

[0055] In the embodiment the initial image 31 is thus subject to image processing in order to be able to evaluate the infrared signature 25 with usual applications or programs.

[0056] In the embodiment in a third method step S3 first a high-pass filtering of the initial image 31 is carried out and thus a high-pass filtered image 32 is created that is illustrated by way of example in FIG. 9. Also in this high-pass filtered image the infrared signature 25 is not or hardly recognizable due to the minor color differences or grey scale differences between adjacent pixels and thus for identification surrounded by dashed lines. As apparent by way of the example of the high-pass filtered image 32 in FIG. 9, the infrared light spot 30 is eliminated in the high-pass filtered image 32 due to the high-pass filtering.

[0057] Subsequent to the high-pass filtering the increase of the contrast in the high-pass filtered image 32 is carried out, whereby a high-pass filtered image 32 is obtained illustrated in FIG. 10 according to the example (fourth method step S4). In this high-contrast image 33 the infrared signature 25 can now already be recognized remarkably better. However, the high-contrast image 33 still contains high-frequent noise components that affect or impede the evaluation of the infrared signature. For this reason the high-contrast image 33 is subject to a blurring in a fifth method step S5, e.g. a Gaussian filtering and/or low-pass filtering and in doing so, from the high-contrast image 33 a blurred image 34 is created that forms a result image 35 according to the example.

[0058] The result image 35 is transmitted to a program or application that is executed by means of the processor 20 of the mobile device 15. The evaluation of the infrared signature 25 is carried out in a sixth method step S6. The application or program evaluates the infrared signature 25 and provides the information contained therein to the user, e.g. on a display of the mobile device 15. The information contained in the infrared signature 25 can also be provided to other programs or applications or can be transmitted by the mobile device 15 by means of wired and/or wireless communication connections to other devices or apparatus.

[0059] In the embodiment of the method according to FIG. 4 the blurred image 34 is used as result image 35. Alternatively to the illustrated method, blurring can also be carried out after capturing of the initial image 31 and prior to the high-pass filtering. It is also possible to carry out blurring after high-pass filtering and prior to increasing the contrast. Thus, the blurring can be carried out after the second method step S2 and prior to the sixth method step S6 at an arbitrary point of the method.

[0060] The increase of the contrast for creation of the high-contrast image 33 is carried out necessarily after high-pass filtering, because otherwise the increase of the contrast without preceding high-pass filtering would result in elimination of the infrared signature 25 contained in the initial image 31.

[0061] The application or program for carrying out the sixth method step S6, i.e. for evaluation of the infrared signature 25, operates preferably as follows:

[0062] First, the obtained result image 35 is transferred in a monochrome matrix. Subsequently, the image section is identified in which the two-dimensional code is contained. Then, for example, the amount of data of the code (number of contained information in Bit) can be determined, e.g. by means of the number of black-white transitions at the edge of the code. Finally, the contained information is read.

[0063] If the program or application for evaluation of the infrared signature should not recognize a usable two-dimensional code in the sixth method step S6, the method is preferably automatically repeated with the first method step S1. If after a predefined number of method routines still no usable two-dimensional code has been recognized in the infrared signature 25, a respective information can be output on the display of the mobile device 15. This information can also be transmitted to other devices or apparatus via a wireless and/or wired interface.

[0064] A difference filter is schematically illustrated in FIG. 5 by means of which a high-pass filtering can be carried out. In the embodiment the difference filter has a size of 3×3 pixels only by way of example. The difference filter can, however, also have a higher number of pixels. The number of pixels in height and width is uneven respectively. The central matrix field corresponds to the pixel of the image (e.g. the initial image 31) subject to the high-pass filtering that is modified in relation to the surrounding pixel in its pixel value. As illustrated in FIG. 5, the sum of the inserted filter values is equal to 0.

[0065] FIG. 6 schematically shows a difference filter that can be used as low-pass filter for an image (e.g. the high-contrast image 33) to be filtered. Thereby mean value is created. Instead of or in addition to the mean value creation, also a Gaussian filtering or the like can be carried out as blurring. Also, the low-pass filter can be selected larger instead of a size of 3×3 pixels, e.g. 4×4 pixels, 5×5 pixels or more. The low-pass filter can have an even or uneven number of pixels per side.

[0066] The high-pass filtering and blurring can be executed separately and separate from one another. Alternatively to this, it is also possible to carry out a band pass filtering in one single step.

[0067] For high-pass filtering and/or blurring also a Fourier transformation, particularly a fast Fourier transformation (FFT) can be realized.

[0068] In an embodiment the following filter parameters can be used in a resolution of the image of 1280×720 pixels: [0069] high-pass filter: 167×167 pixels, adapted to the resolution; [0070] contrast factor 20; [0071] low-pass filter: 13×13 pixels and thus sufficiently small relative to the resolution of the image in order to avoid that the image information of the infrared code is eliminated.

[0072] In FIG. 7 also another possibility for high-pass filtering is illustrated. Thereby an image, e.g. the initial image 31, is subject to a low-pass filtering 36 first, such that from the initial image 31 the blurred image 34 is obtained. The blurred image 34 as well as the initial image 31 are then transferred to high-pass filtering 37. During this high-pass filtering 37 a difference image 38 is created that corresponds to the difference of the initial image 31 minus the blurred image 34. The difference image 38 can subsequently be amplified by addition with a summand or by multiplication with a factor α larger than 1.

[0073] During filtering color information potentially contained in the pixel is ignored. Only the grey scale values of each pixel is considered.

[0074] The invention refers to a method for evaluation of an infrared signature 25 present on an object surface 26 that preferably forms a two-dimensional code. In addition, a one-or multiple-colored pattern can be present on the object surface 26 that reflects light in the visible wavelength range. The infrared signature 25 absorbs light in the infrared range and is thus detectable by means of an IR-camera. During the method an infrared light source 17 is switched on and the infrared signature 25 is illuminated with infrared light L and an initial image 31 is captured by means of the infrared camera 16 in this condition. The initial image 31 or a further processed image based thereon is subsequently subject to a high-pass filtering, whereby directly or indirectly after the high-pass filtering, the contrast in the image is increased. Finally, an evaluation of the infrared signature 25 can be carried out in the image processed in this way.

REFERENCE LIST

[0075] 15 mobile device
16 infrared camera
17 infrared illumination
18 camera
19 light source
20 processor
25 infrared signature
26 object surface
27 object
28 pattern
29 input filter
30 infrared light spot
31 initial image
32 high-pass filtered image
33 high-contrast image
34 blurred image
35 result image
36 blurring
37 high-pass filtering
38 difference image
α factor
L infrared light
S1 first method step
S2 second method step
S3 third method step
S4 fourth method step
S5 fifth method step
S6 sixth method step