Method and device for inspecting lacquered surfaces with effect pigments - Patents.com

Abstract

A method for inspecting a lacquered surface (10), characterized in that radiation is irradiated by a first emission device (2) at a first predetermined illumination angle (a1) onto the surface (10) to be inspected, a color image recording device (4) records a spatially resolved image of the surface illuminated by an illumination direction at a first observation angle (b), this image recording device (4) comprising a first predetermined sensitivity (F(l)) depending on the wavelength of the radiation impinging on the image recording device, and an image evaluation device performs a section-wise, preferably pixel-wise, evaluation of the image recorded by the image recording device.

Description

[Technical field]

[0001] The present invention relates to a method and an apparatus for inspecting lacquered surfaces, in particular such surfaces which preferably have a paint mixture of absorbing and effect pigments. Such lacquer layers have been known in the prior art for a long time. Various methods and apparatus for inspecting and / or analyzing such surfaces are also known from the prior art. [Background technology]

[0002] It is known that the spectral characteristics of an illuminated measuring spot are recorded with a spectroscopic element (e.g. a grating, a prism or a filter) and this is compared, for example, with a standard. It is also known that the measurement results of such measuring methods often differ significantly from one another, on the one hand, because differences between the image recording properties of cameras on the one hand and the human eye on the other hand are not fully taken into account, and on the other hand, because optical filter devices are also significantly different. Summary of the Invention

[0003] There is therefore a need for a procedure which allows the most uniform or characteristic evaluation possible of images of such surfaces. This is achieved according to the invention by the subject matter of the independent patent claims. Advantageous embodiments and further developments are the subject matter of the dependent claims.

[0004] In a method for inspecting lacquered surfaces, in particular surfaces which preferably have one or more layers with absorbing and effect pigments, the surface to be inspected is illuminated by a first emission and / or illumination device at a predefined angle of incidence and / or radiation is irradiated onto said surface, and a color image recording device records a spatially resolved image of the surface illuminated and / or illuminated by the incidence direction at a first observation angle, said image recording device having a first predefined sensitivity depending on the wavelength of the radiation incident on the image recording device.

[0005] According to the invention, an image evaluation device performs a section-wise, preferably pixel-wise, evaluation of said image recorded by said image recording device.

[0006] Preferably, the surface is an exterior surface of an automobile, in particular a lacquered exterior surface of an automobile, especially a passenger car, however, other surfaces such as furniture surfaces can also be inspected.

[0007] Preferably, the results of this evaluation are used or taken into account for (future) measurements by the apparatus used for the evaluation. Preferably, the evaluation determines and / or generates a "filter device", in particular a software filter device, which is taken into account and / or used for (future) measurements.

[0008] For example, as mentioned above, an evaluation relating to the image recording device can be carried out pixel by pixel. This evaluation allows at least one calibration value to be assigned to each pixel or each pixel range for future measurements. This calibration value is preferably determined in the course of the evaluation for each individual pixel. The calibration value determined within the evaluation (in particular for each pixel) can also be taken into account when outputting the measurement result for each individual pixel of the image recording device for future measurements with the device.

[0009] A method is known from the applicant's internal prior art of arranging an optical filter device between a surface and an image recording device. This method is also intended to compensate for the different evaluation characteristics of the human eye on the one hand and the camera on the other hand. However, it has been found that such filter devices themselves have a high dispersion (with respect to their characteristics) and therefore result in different evaluations. Furthermore, corresponding lighting devices such as LEDs also suffer from strong scattering. This means that even two LEDs from the same manufacture, which should themselves be identical, have different beam characteristics. Furthermore, the diversity of RGB filters from camera to camera and even within a single camera is high.

[0010] For this reason, specially adapted filters are needed that take into account changes in camera or light source characteristics (e.g. when the camera chip or LED needs to be replaced). In addition, state of the art also allows only standard light types. By introducing specially matched filters, different standard light types can be mathematically taken into account.

[0011] The invention therefore proposes a section-by-section, in particular pixel-by-pixel, evaluation of the image, in particular also as a function of wavelength, in order to be able to adapt to the respective conditions, i.e. the specific radiation characteristics of the illumination device and also the image recording device or its characteristics. It can be envisaged that said evaluation is repeated, for example carried out at predefined times. The results and / or measurements of the evaluation are preferably stored.

[0012] The image recording device, as known per se from the prior art, comprises an image recording element with a plurality of image pixels, each image pixel being suitable for detecting radiation impinging on the image recording element. For example, the image recording element can comprise a CCD chip. The evaluation is carried out for at least some of said pixels, preferably for at least 30%, preferably for at least 50%, preferably for at least 60%, particularly preferably for at least 70% of said pixels. It is also possible to carry out the evaluation for each of these pixels individually, but it is also conceivable to evaluate a combination of several pixels, thereby reducing the resolution of the evaluation to some extent.

[0013] For example, such image evaluation may be performed at predetermined time intervals.

[0014] In a preferred method, the measurement signals of the individual pixels are weighted taking into account the pixel-by-pixel evaluation. In this way, software filter devices can be used or created, which in particular also influence the image evaluation of subsequent images.

[0015] In a preferred method, the evaluation is carried out as a function of the wavelength of the radiation incident on the image recording device, which means that a wavelength-dependent evaluation of the sensitivity of the image recording device, in particular the sensitivity of each individual pixel, is recorded as a function of the wavelength.

[0016] Particularly preferably, the evaluation is therefore carried out as a function of the wavelength-dependent (in particular pixel-by-pixel) sensitivity of the image-recording device. Preferably, an individual evaluation is carried out for each individual image-recording device. This evaluation is also preferably carried out pixel-by-pixel.

[0017] Preferably, the wavelength-dependent sensitivity of the image recording device is determined. In particular, the sensitivity can be determined pixel by pixel (in particular wavelength-dependently) or the wavelength-dependent sensitivity can be determined for each individual pixel.

[0018] However, it is also possible to perform the evaluation over several pixels, for example averaging over several pixels of the same intensity.

[0019] In a further preferred method, an image recording device, in particular a colour image camera, is also used to evaluate and / or rate the effect pigments.

[0020] In a further preferred method, the influence of the effect pigments on the image recording and / or on the integral colorimetry is taken into account and / or eliminated, especially within the scope of the image evaluation.

[0021] In the state of the art, there is a problem that integral colorimetry can fail, since it is not possible to distinguish whether the resulting measurement results are caused by the color of the flakes or effect pigments or have another cause. The preferred proposed method allows such a distinction. More precisely, for this purpose a spatially resolved colorimetry is performed.

[0022] In integral colorimetry, errors can occur, especially when the effect pigments themselves produce a coloring effect, especially in a color different from the shade caused by the absorption effect.

[0023] For example, a solid color with only one absorbing pigment (eg solid red) and the same absorbing pigment (eg red) with the addition of a colored effect pigment will result in different color values ​​XYZ being measured in integral colorimetry.

[0024] Multi-angle color measuring devices known from the state of the art allow integrated, averaged, non-spatially resolved color measurements over a measuring spot illuminated at several angles. In the history of device development, the first devices were not accompanied by a camera, later a camera device was added. The camera measurements are used here only to evaluate "glint" directed light (direct sunlight) and "granular" (diffuse lighting, cloudy sky) and are additional information unrelated to the color measurements for the characterization of effect pigment lacquers.

[0025] The use of a camera in a multi-angle color measuring device when measuring plain lacquers (containing only absorbing pigments) is unnecessary and only makes sense for effect paints containing a mixture of absorbing pigments and one (or more) types of effect pigments.

[0026] The method proposed here eliminates the influence of the effect pigment measurement on the absorbing pigment measurement, resulting in both measurements giving the same value in the above example.

[0027] In a preferred method, the influence of effect pigment measurements on the absorbent pigment measurements is reduced and / or eliminated.

[0028] In a preferred embodiment, it is proposed within the scope of the present invention that an image recording device, in particular a colour image camera, is also used for evaluating and / or assessing the effect pigments (and in particular their colour properties).

[0029] However, it is preferred that in addition information regarding the color saturation and / or color distribution of areas of the image that are due to and / or contain the effect pigments is obtained, so that these advantages achieved by the use of a color imaging camera can still be maintained.

[0030] Preferably, the wavelength-dependent sensitivity is determined by a spectrometer and / or a monochromator and / or the evaluation of the image recorded by the image recording device is performed by a spectrometer and / or a monochromator.Several procedures for determining the spectral sensitivity of the image recording device, in particular of each individual pixel, are conceivable.

[0031] For example, using the following formula, it is possible to obtain the characteristic curves of the individual channels of an RGB CMOS / CCD camera chip, preferably with a Bayer pattern, as a sum over multiple wavelengths:

number

[0032] where p is the measured value (red, green, blue). i )=s i represents the spectral sensitivity of the pixel / filter combination. E i,j is the wavelength l i 4 shows a calibration tile with known relaxation spectrum number j in

[0033] It is also possible to perform a multiple regression. This can be done using the following equation:

number

[0034] Within the scope of the present invention, it is proposed to determine the spectral sensitivity for each pixel by means of a monochromator and / or a (particularly absolutely calibrated) spectrometer. On the basis of these recorded spectral sensitivities, deviations can be determined in each case, which deviations can be taken into account in the subsequent image evaluation in order to record and / or output colorimetrically corrected images of the individual pixels.

[0035] In a preferred method, to determine the wavelength-dependent sensitivity of an image recording device, a surface is irradiated at a predefined angle to a set of reference planes with known resolution, and the image recording device records an image of the surface. Preferably, the angle is greater than 20°, preferably greater than 30°, preferably greater than 40°, preferably greater than 50°, particularly preferably greater than 60°, relative to the normal.

[0036] Additionally or alternatively, it may be envisaged that the surface is illuminated with further, in particular monochromatic light from external auxiliary light sources. These may be, for example, monochromatic LEDs or white light filtered by a number of band-pass filters. Here too, the illumination angle is preferably greater than 20°, preferably greater than 30°, preferably greater than 40°, preferably greater than 50° and particularly preferably greater than 60° relative to the vertical.

[0037] The reason for acquiring images with illumination at a very large angle relative to the extension direction of the surface to be observed or with very flat illumination is that these surfaces behave under these illuminations in a manner with the least distortion dictated by the effect pigments used in the coating: for example, a silver metal coating consists only of aluminum flakes or flakes partially accompanied by a certain amount of TIO2.

[0038] In this case, under flat illumination or lighting angles, a grey neutral light direction spectrum can be expected. The further surface has a chromatic metal coating with aluminum, which usually has only a small amount of effect pigments. In this case, only a small amount of these flakes are visible at flat illumination angles. The so-called Xylar or MICA coating has even less effect pigments, i.e. in this case, none of these flakes are visible at the mentioned angles. Preferably, image evaluation is carried out separately and / or independently for the absorbing pigments and the effect pigments (flakes).

[0039] Preferably, in the case of an absorbing pigment recipe, the pixel number is recorded and / or stored together with the intensity value assigned or determined thereto (output by the pixel in question). In a further step, a histogram can be recorded and the maximum of the respective frequency determined. In a further step, the mean value XYZ is preferably recorded for a statistically defined number of pixels.

[0040] For the evaluation of effect pigments, flakes that are preferably separated from one another and reach or cover all three filters (i.e. whose emission characteristics or emission maxima are within the respective wavelength ranges of the associated filter devices of the image recording device) are selected and the product XYZ is determined only for these flakes. Preferably, in this case no demosaicing is used. Preferably, at least two images are taken with a specific exposure time.

[0041] Preferably, the color effect of the absorption pigment is assessed in an image taken at a first predetermined angle, in particular an angle away from the gloss, at which angle the colorimetric falsification by the effect pigment is to a good approximation negligible. An angle away from the gloss is understood to be an angle deviating from the direction of reflection by at least 30°.

[0042] The sparkle caused by the effect pigments is preferably identified in a second camera image taken at an angle close to the gloss, which is understood to be an angle that deviates from the direction of reflection by no more than 25°, preferably no more than 20°, preferably no more than 15°.

[0043] Due to the close angle of the sheen, the effect pigments can be identified in the camera image as areas of high intensity (above a certain threshold) i.e. it is known with pixel accuracy whether it is an area on the sample with absorbing or effect pigment.

[0044] In a further advantageous manner, the evaluation and / or measurement with the device takes into account the sensitivity of the human eye depending on the wavelength of the radiation impinging on the human eye.

[0045] In a further preferred method, the data determined in the course of the evaluation are taken into account in order to generate a filter device, in particular a software filter device, for subsequent measurements by an apparatus which also performs an evaluation which calibrates the measured values ​​recorded or determined by the image recording device. Preferably, the recorded images are calibrated pixel by pixel and / or the measured values ​​output by the individual pixels are calibrated individually.

[0046] Thereby, by means of one, in particular said filter device, it is possible for the difference between this first sensitivity (of the image recording device) and the second sensitivity (of the human eye) to be at least partially compensated.

[0047] In a further preferred method, the surface is irradiated by a second irradiating device and a second predetermined irradiation angle, and the image recording device records an image of the surface irradiated by the second irradiating device. Alternatively, a second observation device may be used. Furthermore, preferably, a third irradiating device is also provided for irradiating the surface to be inspected.

[0048] Particularly preferably, the illumination is performed at different angles.In a further preferred method, the at least one emitting device emits directional or diffuse radiation onto the surface.

[0049] In a further preferred method, a data reduction of the data recorded during the evaluation is performed, which data reduction is preferably different for the absorbing pigment and the effect pigment. In this case, the data reduction can be performed, for example, in such a way that during the evaluation of the wavelength-dependent sensitivity of the pixel or during the evaluation of the incident radiation, only wavelength ranges in which certain intensities (determined in particular from the spectral course), for example (local) intensity maxima occur, are examined. In this way, intensity limits that allow the detection of flare-free areas can be determined. In this way, areas of the image that contain images of flakes or areas that are free of flakes are preferably identified.

[0050] When observing surfaces, the problem arises that commercially available image recording devices, such as RGB cameras, have specific wavelength-dependent sensitivities that deviate from the wavelength-dependent sensitivities of the human eye. The aim is therefore to enable the most realistic possible image recording of the illuminated surface (or the most realistic possible evaluation of this image recording).

[0051] The invention therefore proposes to achieve at least partial adaptation of the image recording device to the human eye by means of a filtering device, in particular a software filtering device, in particular such a filtering device that takes into account the recorded data in the course of the evaluation.

[0052] The CIE Standard Valence System or CIE Standard Colour System is a colour system defined by the International Commission on Illumination (CIE-Commission internationale de l'eclairage) to establish a relationship between human colour perception (colour) and the physical causes of colour stimuli (colour). This colour system captures the whole range of perceptible colours. Using colour space coordinates, the terms Yxy colour space or CIE-Yxy, and tristimulus colour space are also commonly used, mainly in English-speaking countries.

[0053] Especially in English-speaking countries, the three base values ​​X, Y, Z are called tristimulus. In this sense, these base values ​​are the three parts of a normalized base color defined (for this purpose). Each color can be identified by three such numbers. The term tristimulus system is therefore commonly used for the CIE standard system. This curve is also called the tristimulus curve.

[0054] Thus, in one embodiment, an image is recorded and individual pixels are evaluated, particularly with respect to color, and a wavelength-dependent evaluation and / or weighting is performed.

[0055] In a preferred method, the evaluation is performed to at least temporarily compensate for a wavelength-dependent difference between the first sensitivity (of the image recording device) and the second sensitivity (of the human eye).

[0056] In this connection it is particularly preferred that the emission spectrum L(λ) of the radiation device, the intensity curve I(λ) of the standard light, in particular at least one tristimulus function X(λ) of the human eye and / or characteristic values ​​or characteristic curves of the filter characteristic F(λ) of the image recording device are taken into account when selecting the filter device.

[0057] Preferably, the wavelength dependent transmittance T(λ) of the filter device provides: T(λ)=X(λ) / (I(λ)·L(λ)·F(λ))

[0058] Here, I(λ) denotes the wavelength-dependent characteristics of the type of light, e.g., D65, L(λ) denotes the wavelength-dependent characteristics of the light source, and F(λ) denotes the observation device (especially the RGB filter), e.g., indicates the wavelength-dependent characteristics of the filter, and X(λ) indicates the wavelength-dependent light sensitivity of the eye (tristimulus function).

[0059] Preferably, the wavelength-dependent properties of the viewing device and the wavelength-dependent light sensitivity of the eye have different functions over at least two, preferably three, predetermined wavelength ranges.

[0060] Preferably, the first wavelength range extends from 300nm-600nm, preferably from 350nm-550nm, preferably from 400nm-500nm. Further, preferably, the second wavelength range extends from 400nm-700nm, preferably from 450nm-650nm, preferably from 500nm-650nm, preferably from 530nm-600nm. Further, preferably, the third wavelength range extends from 500nm-900nm, preferably from 550nm-800nm, preferably from 600nm-700nm.

[0061] It is preferable to cover the entire perceptual range of the human eye.

[0062] In a further preferred method, radiation is irradiated onto the surface by a second radiation device at a second predetermined radiation angle, and an image recording device records an image of the surface irradiated by the second radiation device.

[0063] Preferably, the first and second radiation devices irradiate the surface at different times or durations.Alternatively or additionally, it is also conceivable that the second image recording device observes the surface at a second observation angle.

[0064] It is also possible to detect effects resulting from different aligned effect pigments by illuminating with two or more emitting devices.

[0065] In a further preferred method a third emitting device is also provided, preferably adapted to emit radiation onto the surface at a third angle of incidence.

[0066] In a further preferred method, the observation angle relative to the normal to the surface is smaller than 10°, preferably smaller than 5°, preferably smaller than 3°.

[0067] In a more preferred method, the first angle of incidence relative to the direction perpendicular to the surface is from 70° to 20°, preferably from 60° to 30°, and preferably from 50° to 40°.

[0068] Preferably, the second angle of incidence of the second emitting device relative to the direction normal to the surface is between 85° and 50°, preferably between 85° and 60°, preferably between 85° and 70°.

[0069] Preferably, at least one radiation device directs directional or diffuse radiation towards the surface. Using diffuse radiation, solar radiation under cloudy skies can be simulated, and using directed radiation, solar radiation under cloudy skies can be simulated.

[0070] Preferably, at least one further radiating device, preferably all radiating devices, directs diffuse radiation or in particular directional radiation onto the surface.

[0071] The invention further relates to an apparatus for inspecting lacquered surfaces comprising a mixture of absorbing pigments and at least one further effect pigment, comprising a first radiation device for irradiating radiation onto the surface to be inspected at a first predetermined irradiation angle, and a colour image recording device for obtaining a spatially resolved image of the surface illuminated by the irradiation direction at the first observation angle, the colour image recording device for recording the spatially resolved image of the surface illuminated by the irradiation direction at the first observation angle, the colour image recording device comprising a first predetermined sensitivity which is dependent on the wavelength of the radiation impinging on the image recording device.

[0072] According to the invention, the apparatus comprises an image recording device which performs a section-by-section, preferably pixel-by-pixel, evaluation of the image recorded by said image recording device.

[0073] In a preferred embodiment, the apparatus comprises a memory device in which the measurement values ​​determined by the evaluation device are stored. Preferably, the memory device allows these measurement values ​​to be stored pixel by pixel.

[0074] In a further preferred embodiment, the apparatus has a filter device, in particular a software filter device, which calibrates the further image recorded by the image recording device, in particular taking into account values ​​determined by the evaluation device and / or values ​​suitable and intended for this purpose.

[0075] Preferably, the filtering device (and / or the processor device implementing this filtering device) is suitable and intended for pixel-by-pixel calibration of the recorded images.

[0076] Preferably, this filter device is modifiable, i.e. in particular the way in which it influences the image output by the image recording device is modifiable, which means that by modifying the (software) filter device it is also possible to modify the image output by the image recording device and / or the measurements output by the entire apparatus.

[0077] Preferably, the apparatus can be operated in a calibration mode in which an evaluation of the images recorded by the image recording device and a determination and / or modification of the software filter device is performed. Preferably, the apparatus can also be operated in an operation mode in which the software filter device determined in particular in the calibration mode is applied.

[0078] Preferably, the apparatus is a multi-angle measuring device, i.e. suitable and intended for inspecting a surface from several (illumination and / or illumination) angles.

[0079] Preferably, the apparatus is "backwards" compatible with apparatus using black and white image capture devices, in particular measurements obtained with the present invention can be compared with measurements obtained with black and white imaging recording devices.

[0080] However, the invention can also be used for plain lacquers (not containing effect pigments) on automobiles (or other surfaces).

[0081] In a further preferred embodiment, the image recording device has a filter, in particular an RGB filter. Preferably, the emitting device emits standard light, in particular D65 standard light. Standard light is a term used to describe a standardized spectral radiation distribution curve of a characteristic radiator. D65 standard light is a radiation distribution with a color temperature of 6504 Kelvin (approximately corresponding to a gray sky).

[0082] In a preferred embodiment, the distance between the surface and the emitting device is between 3 cm and 30 cm, preferably between 4 cm and 20 cm, preferably between 4 cm and 10 cm.

[0083] In a preferred embodiment, the emission devices are suitable and adapted to emit radiation of different wavelengths. A filter device may be provided, such as a filter wheel having different filters that allow only light of certain wavelengths to pass.

[0084] In a further preferred embodiment, the first emitting device comprises a light emitting diode (LED), in particular a triphosphor LED. Preferably, the device also comprises further emitting devices, as described above. These emitting devices preferably comprise light emitting diodes, in particular triphosphor LEDs.

[0085] In a further preferred embodiment, the apparatus comprises at least one second radiation device and / or a second sensor device, which can be designed as an image recording device, but it is also conceivable that this sensor device is a sensor device which determines the intensity of the radiation incident on it.

[0086] In a further preferred embodiment, the apparatus comprises at least three emitting devices (or illumination devices) which preferably illuminate the surface at at least three different angles.

[0087] In a further preferred embodiment, the filter device performs a pixel-by-pixel calibration of values ​​or signals output from individual pixels of the image recording device. [Brief description of the drawings]

[0088] Further advantages and embodiments can be seen in the accompanying drawings. [Figure 1] 1 shows a schematic diagram of an apparatus according to the present invention. [Diagram 2] FIG. 1 is a diagram showing the spectral characteristics of RGB filters of a digital camera. [Diagram 3] The sensitivity curves of three color receptors X (red), Y (green), and Z (blue) are shown. [Figure 4]1 shows a representation of the radiant power of the standard illuminant D65. [Diagram 5] The emission spectrum of the LED is shown. [Figure 6] 1 shows the transmission behavior of a filter device. [Figure 7a] A comparison of the resulting sensitivities is shown. [Figure 7b] A comparison of the resulting sensitivities is shown. [Figure 7c] A comparison of the resulting sensitivities is shown. [Figure 8a] 1 shows a comparison of theoretical and actual strength curves. [Figure 8b] FIG. 2 is a diagram illustrating the deviation between the theoretical course and the actual course. [Figure 9] 1 shows a histogram representation of a metal lacquer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0089] 1 shows a schematic diagram of an apparatus 1 for inspecting a surface 10. The apparatus comprises a first emission or illumination device 2 which emits light onto the surface 10 beam S2.

[0090] Reference 4 denotes an image recording device which records at least one spatially resolved image of the surface illuminated by the first radiation device (beam path S4). Reference O denotes an opening in the housing 12, through which the surface 10 is illuminated and observed by the image recording device 4. The image recording device records images at an observation angle of 0°, i.e. is positioned vertically above the surface 10.

[0091] Reference number 12 denotes a filter device arranged in the beam path S4 between the surface 10 and an image recording device, through which the image recording device records an image of the surface 10.

[0092] Reference number 14 denotes an optionally present lens device that serves to collimate the light reflected and / or scattered by surface 10 so that it enters the filter device in a collimated manner, preferably also perpendicular to the filter device.

[0093] Reference number 20 denotes an evaluation device for evaluating the image recorded by the image recording device 4. The evaluation device is preferably capable of outputting characteristic data regarding the physical properties of the surface.

[0094] Reference number 22 identifies a processor device which calibrates and / or corrects the images acquired by the image recording device in the operating mode of the apparatus, in particular calibrating and / or correcting them pixel by pixel taking into account the data determined by the evaluation device. This processor device therefore preferably determines the aforementioned software filter device.

[0095] Reference number 6 denotes a second radiation device which emits radiation, in particular light, onto the surface (at a different angle of incidence or along the beam path S2), which radiation device can in particular be used for evaluating the recorded images.

[0096] Reference number 8 denotes a third emitting device which emits radiation, in particular light, along a beam path S3 onto a surface 10.

[0097] Preferably, a control device (not shown) is provided which operates the radiating devices 2, 6 and 8 with a time delay.

[0098] 2 shows the characteristics of an image recording device depending on the wavelength of the incident radiation, more precisely the sensitivity of the RGB filters of this image recording device or camera is shown.

[0099] Shown are three curves R, G, B, referring to the "red", "green" and "blue" components. The quantum efficiency (%) is plotted on the coordinates and the wavelength of the incident light is plotted on the coordinates.

[0100] It can be seen that the quantum efficiency of the whole camera first increases in the wavelength range of 400 nm to 800 nm and then decreases again. Thus, the image recording device has a unique feature of image reproduction or image recording.

[0101] Figure 3 shows a representation of the tristimulus function of the human eye. Here again, three curves x(λ), y(λ) and z(λ) are shown, with the wavelength in nm plotted on the horizontal axis and the tristimulus values ​​plotted on the vertical axis.

[0102] Comparing the diagrams in Figures 2 and 3, it can be seen that the wavelength-dependent sensitivity curves of image recording devices and the human eye differ considerably. These differences should be at least partially compensated for by the present invention.

[0103] Figure 4 shows a diagram of the intensity curve of the D65 standard light source in the range from 300 nm to 800 nm. This type of light is approximated by the curves of daylight and cloudy sky. The second curve A shows the course of a conventional light bulb.

[0104] Standard Illuminant D represents the daylight spectrum and is therefore of particular importance for many industrial areas. Illuminant D65 derives its name from its color temperature of 6,504 Kelvin (K). D65 is used in the chemical and pharmaceutical industries, in paint production, in the ceramic, textile, paper and automotive industries.

[0105] Standard illuminant D65 has a high blue content that allows the fluorescent colors to be perceived. D65 is used as the evaluation light source. The spectral distribution of the D65 light source is specified in DIN 5033 and lies between 300 nm and 780 nm wavelengths, and therefore between the ultraviolet and red light.

[0106] Figure 5 shows the emission spectrum of a light source preferably used in connection with the present invention, namely a triphosphor high CRI LED. It can be seen that this light source essentially emits between 400 and 800 nm. This results in a relative radiant intensity plotted on the 400 nm coordinate that is substantially greater than 50%. The color temperature here is 5600 K. This emission characteristic is preferably also taken into account in the design of the filter device.

[0107] The abbreviation CRI stands for Color Rendering Index. Color rendering index is a quantitative measure of a light source and its ability to render the color of an object compared to an ideal or natural light source. The term CRI is often used for commercial lighting products. When properly defined, it should be called Ra - general color rendering index - or Ri - specific color rendering index - depending on the test color sample being evaluated.

[0108] CRI is calculated by comparing the color rendering of a test light source to that of a given light source. For test light sources below 5000K, a blackbody radiator is used as the given comparison light source. For test light sources above 5000K, daylight (D lamp) is used for comparison. The calculation of Ri and Ra is explained in detail in CIE Technical Report 13.3-1995. The test method uses a set of 8 Ra or 14 Ri CIE-1974 color samples from an early version of the Munsell color system. The first 8 samples are moderately saturated, make up a hue circle, and have approximately equal luminance. The remaining 6 samples provide further information on the color rendering of the light source.

[0109] Figure 6 shows the transmission curve of a filter device according to the present invention, calculated from the above data and the above formula. Based on this data, a filter device is preferably manufactured that exhibits approximately the transmission behavior shown in Figure 6. In manufacturing a filter device, there are several ways to achieve the desired transmission curve, which have been explained above.

[0110] Figures 7a to 7c show three representations of the gradient (plotted in arbitrary units on the coordinates). Figure 7b shows again the course of the human eye also shown in Figure 3. Figure 7c shows the course resulting from an image recording device without the filter device proposed according to the invention. Figure 7a shows the sensitivity or course resulting when using a filter device. It can be seen that the curve shown in Figure 7a is much closer to the "natural" curve shown in Figure 7b than the curve shown in Figure 7c.

[0111] Figure 8a illustrates the method according to the invention. A comparison between the curves shown in Figures 7b and 7c is shown in more detail. It can be seen that the curves are close to each other in some wavelength ranges, but quite different in others. The tristimulus curves X, Y, Z are shown, while the resulting sensitivity curves B, G, R are shown.

[0112] Figure 8b shows a representation of the percentage deviations of the curves from each other diff x, diff y, diff z. Again, it can be seen that in some regions there is a large deviation and in other regions there is only a small deviation.

[0113] As mentioned before, the measured spectra were recorded under a very flat incidence angle, where the contribution of individual flakes is very small.

[0114] The X, Y, and Z values ​​can be determined using the following equations:

number

[0115] The following applies to K:

number

[0116] FIG. 9 is an illustration of data reduction by histogram calculation from 2D image data. A typical histogram of a metal coating (containing absorbing and effect pigments) is shown. A strong peak can be seen with a local maximum in the intensity value range between about 30 and 100 grey values ​​that can be assigned to absorbing pigment image pixels. Above a certain grey value threshold, which is a certain distance from the maximum of the absorbing pigment peak, the histogram channel contains only pixels that can be assigned to effect pigments. For data reduction, only the area below the grey value threshold can be used for the evaluation of the effect pigment influence.

[0117] In a further method step, the area of ​​this maximum is selected for the evaluation of the absorbing pigment and the value L*a*b is calculated and averaged over this area for a sufficient number of pixels. This procedure makes it possible to distinguish between areas of the image which reproduce flakes and areas which do not, as previously described.

[0118] For evaluation of a flake or a layer containing flakes, as discussed above, a separate flake is preferably selected, for example a particular region of pixels can be assigned to the flake.

[0119] The applicant reserves the right to claim as essential to the invention all features disclosed in the application documents, if they are new, either individually or in combination, compared to the prior art. It is further noted that the individual figures also describe features that may be advantageous in themselves. Those skilled in the art will immediately recognize that a particular feature described in a figure may be advantageous without adopting further features from this figure. Moreover, those skilled in the art will recognize that advantages may also result from a combination of several features shown in the individual figures or in different figures.

Claims

1. A method for inspecting a lacquered surface (10) preferably comprising one or more layers with absorption pigments and / or effect pigments, wherein radiation is irradiated onto the surface (10) to be inspected at a first predetermined irradiation angle (a1) by a first radiation device (2), and a color image recording device (4) records a spatially resolved image of the surface irradiated by the irradiation direction at a first observation angle (b), and this image recording device (4) includes a first predetermined sensitivity (F(l)) depending on the wavelength of the radiation impinging on the image recording device, characterized in that an image evaluation device performs an evaluation for each section, preferably for each pixel, of the image recorded by the image recording device.

2. The method according to claim 1, characterized in that the evaluation is performed according to the wavelength of the radiation impinging on the image recording device and / or according to the wavelength-dependent sensitivity of the image recording device.

3. The method according to claim 1, characterized in that the wavelength-dependent sensitivity of the image recording device is determined, in particular for each section, in particular for each pixel.

4. The result of the evaluation performed by the image evaluation device is determined and / or generated by an evaluation of a filter device that is used and / or considered for measurement, preferably considered and / or used for measurement, according to any one of claims 1 to 3.

5. The method according to any one of claims 1 to 3, characterized in that the color image recording device (4) is also used for evaluating and / or rating the effect pigments, and / or the influence of the effect pigments on image recording and / or integral colorimetry is considered and / or excluded within the scope of the image evaluation.

6. The method according to any one of claims 1 to 3, characterized in that the wavelength-dependent sensitivity of the image recording device is determined by a spectrometer and / or a monochromator, and / or the evaluation of the image recorded by the image recording device is performed by a spectrometer and / or a monochromator.

7. To determine the wavelength-dependent sensitivity of the image recording device, the surface is irradiated with radiation at a predetermined angle onto a set of reference surfaces with known reflectance. Preferably, the image recording device records an image of the surface, or preferably, the angle is greater than 20°, preferably greater than 30°, preferably greater than 40°, preferably greater than 50°, preferably greater than 60° with respect to the vertical direction. The method according to any one of claims 1 to 3, characterized in that.

8. The evaluation is characterized by taking into account the sensitivity (X(l)) of the human eye that depends on the wavelength of the radiation incident on the human eye. The method according to any one of claims 1 to 3.

9. The surface is irradiated with radiation by a second radiation device (14) at a second predetermined irradiation angle (a2), and the image recording device records an image of the surface irradiated by the second radiation device (14). The method according to any one of claims 1 to 3, characterized in that.

10. The filter device takes into account the emission spectrum L(l) of the radiation device, the intensity curve I(l) of standard light, in particular at least one tristimulus function X(l) of the human eye, and / or the filter characteristics F(l) of the image recording device. The method according to any one of claims 1 to 3, characterized in that.

11. The observation angle (b) with respect to the direction perpendicular to the surface (10) is less than 10°, preferably less than 5°, preferably less than 3°, and / or the first incident angle with respect to the direction perpendicular to the surface is 70° to 20°, preferably 60° to 30°, preferably 50° to 40°. The method according to any one of claims 1 to 3, characterized in that.

12. Data reduction of the data recorded during the evaluation process is performed, and this data reduction is preferably different for the absorption pigment and the effect pigment. The method according to any one of claims 1 to 3, characterized in that.

13. An apparatus (1) for inspecting a lacquered surface (10) preferably comprising one or more layers with absorption pigments and / or effect pigments, the apparatus (1) comprising a first radiation device (2) for irradiating the surface (10) to be inspected with radiation at a first predetermined irradiation angle (a1), and a color image recording device (4) for recording a spatially resolved image of the surface irradiated by the irradiation direction at a first observation angle (b), the image recording device (4) having a first predetermined sensitivity (F(l)) depending on the wavelength of the radiation impinging on the image recording device, An apparatus (1) characterized by having an image evaluation device (20) for performing an evaluation for each section, preferably for each pixel, of the image recorded by the image recording device. Claim 14 The apparatus (1) according to claim 13, further comprising a filter device for calibrating further images recorded by the image recording device, in particular for calibrating those further images taking into account the values determined by the evaluation device, and / or being suitable and intended for this purpose, the filter device preferably being changeable. Claim 15 The apparatus (1) according to claim 13 or 14, characterized in that the filter device performs a pixel-by-pixel calibration of the values or signals output by the individual pixels of the color image recording device.

Images