Method and apparatus for inspecting a surface - Patents.com

Abstract

A method for inspecting surfaces, in particular surfaces of motor vehicles having effect pigments, characterized in that the surface to be inspected is irradiated with radiation by a first emitting device at a first predetermined emission angle, a color image recording device records a spatially resolved image of the surface illuminated by the radiation direction at a first observation angle, the image recording device having a first predetermined sensitivity (F(λ)) which is different from a second predetermined sensitivity (X(λ)) which depends on the wavelength of the radiation impinging on the image recording device and which depends on the wavelength of the radiation impinging on the human eye, and in that the difference between the first sensitivity (F(λ)) and the second sensitivity (X(λ)) is at least partially compensated by a filter device.

Description

[Technical field]

[0001] The present invention relates to a method and apparatus for inspecting surface properties. Although the invention is described in relation to vehicle surfaces, it should be noted that the apparatus can also be applied to other surfaces such as furniture. [Background technology]

[0002] Coatings with effect pigments have been known in the state of the art for some time. These have different optical properties depending on the viewing angle. A wide variety of inspection devices for inspecting such surfaces are also known. Such inspections can be carried out, for example, to produce lacquers for damaged surfaces.

[0003] Thus, there is a need for testing procedures and devices that allow for standardized evaluation of such surfaces. Summary of the Invention

[0004] The invention is based on the object of enabling the most accurate possible evaluation of a surface. In particular, the observation properties of the human eye are taken into account. In particular, a realistic color impression of the surface to be inspected should also be possible.

[0005] According to the invention, this is achieved by a method and an arrangement according to the independent claims. Advantageous embodiments and further developments are the subject of the dependent claims.

[0006] In the method for inspecting surfaces, in particular surfaces of motor vehicles having effect pigments, according to the invention, radiation is irradiated by a first emitting device at a first predetermined emission angle to the surface to be inspected, a colour image recording device records a spatially resolved image of the surface illuminated by the radiation direction at the first observation angle, the image recording device having a first predetermined sensitivity which is different from a second predetermined sensitivity (of the human eye) which depends on the wavelength of the radiation impinging on the image recording device and which depends on the wavelength of the radiation impinging on the human eye.

[0007] According to the invention, the difference between the first sensitivity and the second sensitivity is at least partially compensated for by the filter device.

[0008] 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 sensitivity 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).

[0009] The invention therefore proposes to achieve an at least partial adaptation of the image recording device to the human eye by means of a filter device.

[0010] 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.

[0011] 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.

[0012] Preferably, the filter device is an optical filter device arranged in the beam path between the emission device and the observation device. However, it is also conceivable that the filter device is a component of an evaluation device for evaluating the image recorded by the image recording device, the filter device preferably being able here to perform a wavelength-dependent sensitivity weighting, in which case the image recorded by the image evaluation device is weighted pixel-by-pixel accordingly.

[0013] Thus, in this embodiment, the image is recorded and the individual pixels are evaluated, in particular with respect to color, and a wavelength-dependent evaluation and / or weighting is performed.

[0014] In a further preferred method, the filter device influences the evaluation of the image recorded by the image recording device. Preferably, the image is evaluated section by section, in particular pixel by pixel. Within this evaluation, a weighting can be performed pixel by pixel. In particular, the weighting can be performed depending on the wavelength of the light incident on the image recording. Preferably, different pixels of the recorded image are weighted differently.

[0015] It is also possible to use both optical and "software" filter devices, for example, to achieve even improved matching compared to optical filter devices.

[0016] In a preferred method, the filter device is arranged between the surface to be inspected and the image recording device. In this embodiment, the filter device is therefore preferably an optical element integrated in the beam path and through which the radiation preferably passes.

[0017] That is, it is preferable for the image recording device to observe the surface through a filter device.

[0018] This filter device preferably has a wavelength-dependent transmittance, which has the effect that the light reaching the observation device is already adapted depending on the wavelength of the light, such that differences between the observation of a human observer and the observation device, in particular under natural ambient conditions, are at least partially compensated for on the other hand.

[0019] Preferably, within the wavelength range of 200 nm-1000 nm, the filter device has a transmittance that varies within this wavelength range as a function of wavelength.

[0020] A wavelength range is understood to be the wavelength range of the radiation, in particular of the light, irradiated onto the filter device. Preferably, the filter device has a transmittance, at least in some regions, preferably continuously, in the wavelength range from 800 nm to 1000 nm, preferably from 700 nm to 1000 nm, which transmittance is less than 20% (relative to the irradiating light intensity), preferably less than 15%, preferably less than 10%, particularly preferably less than 5%.

[0021] Preferably, the filter device has a transmittance in the wavelength range 200 nm-400 nm that is less than 20% (relative to the illuminating light intensity) in at least some regions.

[0022] Preferably, in the wavelength range 400 nm-700 nm, the filter device comprises at least one (wavelength) sub-region, preferably at least two wavelength sub-regions, with a transmittance of more than 80%, preferably more than 85%, preferably more than 90%, preferably more than 95%. Preferably, in the wavelength ranges 450 nm and 650 nm, the filter device has at least one wavelength sub-region with a transmittance of less than 40%, preferably less than 30%, preferably less than 20%, preferably less than 15%.

[0023] Preferably, in the wavelength range of 400 nm-700 nm, the filter device has both at least one wavelength subrange with a transmittance of more than 80% and at least one wavelength subrange with a transmittance of less than 20%.

[0024] In a preferred method, the varying transmittance is selected to at least temporarily compensate for the wavelength-dependent difference between the first and second sensitivities.

[0025] 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.

[0026] Preferably, the wavelength dependent transmittance T(λ) of the filter device provides: T(λ)=X(λ) / (I(λ)·L(λ)·F(λ))

[0027] Here, I(λ) denotes the wavelength-dependent properties of the type of light, e.g. D65, L(λ) denotes the wavelength-dependent properties of the light source, F(λ) denotes the wavelength-dependent properties of the viewing device (especially RGB filters, and especially those filters), and X(λ) denotes the wavelength-dependent light sensitivity of the eye (tristimulus function).

[0028] 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.

[0029] 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.

[0030] In this case, it is preferable to cover the entire perceptual range of the human eye.

[0031] In a further preferred method, the radiation impinging on the filter device is influenced, in particular refracted, by a refractive optical element, preferably arranged between the surface and the filter device. Preferably, the radiation is diffracted such that it impinges on the filter device substantially parallel or parallel. Preferably, the radiation impinges on the filter device perpendicularly.

[0032] 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.

[0033] 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.

[0034] It is also possible to detect effects resulting from different aligned effect pigments by illuminating with two or more emitting devices.

[0035] In a further preferred method a third emitting device is also provided, preferably emitting radiation at a third emission angle onto the surface.

[0036] 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°.

[0037] 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°.

[0038] Preferably, the second emission angle of the second emitting device relative to a direction normal to the surface is between 85° and 50°, preferably between 85° and 60°, preferably between 85° and 70°.

[0039] 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.

[0040] Preferably, at least one further radiating device, preferably all radiating devices, directs diffuse radiation or in particular directional radiation onto the surface.

[0041] The invention further relates to an apparatus for inspecting surfaces, in particular surfaces of motor vehicles with effect pigments, comprising a first radiation device for irradiating the surface to be inspected with radiation at a first predetermined radiation angle and a colour image recording device (e.g. an RGB camera) for recording a spatially resolved image of the surface illuminated by the radiation direction at a first observation angle, the image recording device having a first predetermined sensitivity which depends on the wavelength of the radiation impinging on the image recording device and which differs from a second predetermined sensitivity which depends on the wavelength of the radiation incident on the human eye.

[0042] According to the invention, the apparatus comprises a filter device which at least partially compensates for the difference and / or deviation between the first sensitivity and the second sensitivity.

[0043] The effect pigments can be, for example, pigments made of TiO2.

[0044] By at least partial compensation it is understood that the average deviation and / or deviation integrated over the wavelength range of 400 nm to 700 nm is reduced by use of the filter device, preferably by at least 20%, preferably by at least 40%, preferably by at least 60%.

[0045] 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.

[0046] 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.

[0047] However, the present invention may also be used on automotive basecoats (or other surfaces).

[0048] Typically, filters absorb unwanted light by adding colored glass or dyes, or reflect unwanted light using interference coatings. It is therefore possible to use specially designed interference coatings and / or selected materials to achieve the desired transmission profile.

[0049] For example, hard-coated optical filters can be used that have a substrate with a dense coating and excellent optical performance. Traditionally, coated optical filters generally consist of several layers of absorbing materials, interference coatings, and metal layers stacked together to form a low-cost, efficient filter.

[0050] Colored glass filters, as well as other absorptive filters such as plastic filters and Latin filters, contain elements, components, dyes or other colorants within the source substrate to affect the spectral characteristics of the filter.

[0051] Optical filter devices can be divided into two main categories: absorptive filters and dichroic filters. The difference between the two variants lies in the type of blocking. With absorptive filters, light is absorbed by the glass used and converted into internal energy or heat. Absorptive filters are ideal for applications where noise from unwanted light is an issue. Absorptive filters also have the advantage that blocking is angle independent. Light can hit the filter at a wide range of angles and the filter still retains its transmission and absorption properties.

[0052] Dichroic filter devices, on the other hand, reflect undesired wavelengths and allow the desired part of the light spectrum to pass. In this way, both wavelength ranges can be used separately. This is achieved by the coating of the filter, which has one or more thin layers of different materials with different refractive indices. The resulting partial reflections interfere specifically with certain wavelength ranges, suppressing reflection or transmission.

[0053] In contrast to absorptive filters, dichroic filters are angle-dependent. If light strikes a dichroic filter with an angle of incidence different from that intended in the design, the effective layer thickness changes, and therefore the design wavelength. For this reason, the aforementioned lenses are advantageously used to collimate the light reaching the filter device. Furthermore, polarization dependence can increase.

[0054] In a preferred embodiment, the filter device is a NG (Neutral Density Glass) filter or also comprises a neutral density glass filter element. Preferably, the filter device is positioned such that radiation emanating from the surface strikes the filter device perpendicularly.

[0055] Preferably, the emission device, the observation device and the filter device are arranged in a common housing. Preferably, the inner wall of this housing is light absorbing. In a further preferred embodiment, the housing has essentially only one opening through which the surface is observed. In a further preferred embodiment, the device is portable.

[0056] 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).

[0057] In a further advantageous embodiment, the apparatus comprises an evaluation device for evaluating the images recorded by the image recording device.

[0058] 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.

[0059] 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.

[0060] In a further advantageous embodiment, a refractive element, in particular a lens, is arranged between the surface (to be inspected) and the filter device. This lens preferably causes the light (scattered by the surface) to impinge on the filter essentially collinearly. It is possible to design the lens and the filter device as a unit.

[0061] 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.

[0062] 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 impinging on it.

[0063] 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. [Brief description of the drawings]

[0064] 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] This shows the spectral characteristics of the 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 7] A comparison of the resulting sensitivities is shown. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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 impinges on the filter device in a collimated manner, preferably also perpendicular to the filter device.

[0069] 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.

[0070] Reference number 6 denotes a second emitting device which emits radiation, in particular light, onto the surface (at a different angle of incidence or along a beam path S2).

[0071] Reference number 8 denotes a third emitting device which emits radiation, in particular light, along a beam path S3 onto a surface 10.

[0072] Preferably, a control device (not shown) is provided which operates the radiating devices 2, 6 and 8 with a time delay.

[0073] 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.

[0074] 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.

[0075] 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. Thus, the image recording device has a unique feature of image reproduction or image recording.

[0076] 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.

[0077] A comparison of the diagrams in Figures 2 and 3 shows 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.

[0078] Figure 4 shows a diagram of the intensity profile of the D65 standard light source in the range from 300 nm to 800 nm. This type of light is approximated to the profile of daylight and cloudy sky. The second curve A shows the profile of a conventional incandescent lamp.

[0079] 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.

[0080] 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.

[0081] 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 radiation characteristic is preferably also taken into account in the design of the filter device.

[0082] 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 colors 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.

[0083] 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 spotlight 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, encompass the color circle, and have approximately equal luminance. The remaining 6 samples provide further information on the color rendering of the light source.

[0084] Figure 6 shows the permeation process 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 permeation behavior shown in Figure 6. In manufacturing a filter device, there are several ways to achieve the desired permeation path, which have been described above.

[0085] 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 course shown in Figure 7a is much closer to the "natural" course shown in Figure 7b than the course shown in Figure 7c.

[0086] 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 surface (10), in particular a surface of a motor vehicle having effect pigments, comprising the steps of:

1. A method in which a surface (10) to be inspected is irradiated with radiation by a first irradiating device (2) at a first predetermined radiation angle (a1), and a color image recording device (4) records a spatially resolved image of said surface irradiated by the radiation direction at a first observation angle (b), said image recording device (4) having a first predetermined sensitivity (F(λ)) which depends on the wavelength of the radiation impinging on said image recording device and which differs from a second predetermined sensitivity (X(λ)) which depends on the wavelength of the radiation impinging on the image recording device and which depends on the wavelength of the radiation impinging on the human eye, 13. The method of claim 12, wherein the difference between said first sensitivity (F(λ)) and said second sensitivity (X(λ)) is at least partially compensated for by a filter device (6).

2. 2. The method according to claim 1, characterized in that the filter device (6) is arranged between the surface (10) and the image recording device (4).

3. 2. The method according to claim 1, characterized in that the filter device influences the evaluation of the image recorded by the image recording device.

4. Method according to any one of claims 1 to 3, characterized in that the filter device (6) has a transmittance in the wavelength range of 200 nm-1000 nm which varies within this wavelength range as a function of the wavelength.

5. 5. The method of claim 4, wherein the varying transmittance is selected to at least temporarily compensate for a wavelength-dependent difference between the first sensitivity and the second sensitivity.

6. The method according to any one of claims 1 to 3, characterized in that the radiation impinging on the filter device (6) is influenced, in particular refracted, by a refractive optical element (12) arranged between the surface (10) and the filter device (6).

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

8. 4. The method according to claim 1 , characterized in that the filter device takes into account the emission spectrum L(λ) of the radiation device, the intensity profile I(λ) of a standard light, in particular at least one tristimulus function X(λ) of the human eye and / or a filter characteristic F(λ) of the image recording device.

9. 4. The method according to claim 1, wherein the observation angle (b) with respect to a direction normal to the surface (10) is smaller than 10°, preferably smaller than 5°, preferably smaller than 3°, and / or the first angle of incidence with respect to a direction normal to the surface is between 70° and 20°, preferably between 60° and 30°, preferably between 50° and 40°.

10. Method according to any one of claims 1 to 3, characterized in that at least one emitting device directs directional or diffuse radiation towards the surface (10).

11. An apparatus for inspecting a surface (10), in particular a surface of a motor vehicle having an effect pigment, comprising:

1. An apparatus comprising a first radiation device (2) for irradiating a surface (10) to be inspected with radiation at a first predetermined radiation angle (a1), and a color image recording device (4) for recording a spatially resolved image of said surface illuminated by the radiation direction at a first observation angle (b), said image recording device (4) having a first predetermined sensitivity which depends on the wavelength of said radiation impinging on said image recording device and which differs from a second predetermined sensitivity which depends on the wavelength of said radiation incident on the human eye, 13. An apparatus comprising: a filter device for at least partially compensating for a difference between the first sensitivity and the second sensitivity.

12. 12. Apparatus according to claim 11, characterized in that the filter device is arranged in the beam path between the surface (10) and the image recording device (4).

13. 12. Apparatus (1) according to claim 11, characterized in that a refractive element, in particular a lens, is arranged between the surface (10) and the filter device.

14. Apparatus (1) according to any one of claims 11 to 13, characterized in that the first emitting device comprises a light emitting diode (LED), in particular a triphosphor LED.

15. Apparatus (1) according to any one of claims 11 to 13, characterized in that it comprises at least one second emitting device and / or a second sensor device.

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