Method and apparatus for suppressing aliasing errors in images from pixelated displays and for evaluation of such displays - Patents.com

Abstract

The present invention relates to a method for suppressing aliasing errors in a moiré-corrected result image formed by at least one camera image, which is captured by a camera (1) with imaging optics (1.1) and a sensor surface (1.2) with sensor pixels (1.3) as an image of a display image of a display device (2) with display pixels (2.1), the display pixels being arranged in a matrix with a display pixel pitch (D A ) on the sensor plane (1.2). During capture, the camera (1) is shifted relative to the display device (2) along at least one offset path (VP) with respect to a starting position (S). The present invention relates to a method for assessing the display quality of a pixel-based display device (2) and to a device for implementing such a method.

Description

[Technical field]

[0001] The present invention relates to a method for suppressing aliasing errors in a moiré-corrected resultant image formed from at least one camera image captured by a camera from a display image displayed by a pixel-type display device in which display pixels are arranged in a matrix.

[0002] The invention further relates to a method for assessing the display quality of a pixel-based display device based on at least one resultant image thus produced.

[0003] Furthermore, the invention relates to an apparatus for carrying out such a method. [Background technology]

[0004] When a display image displayed by a display device having display pixels arranged in a matrix is ​​recorded by a camera including a sensor having sensor pixels arranged in a matrix, aliasing artifacts called Moire interference, Moire phenomenon, or Moire for short, may occur. Such aliasing errors are particularly likely to occur when the sensor pixels of the camera are of The pixel pitch, i.e., the distance from the center of a first pixel to the center of an adjacent second pixel, is the pixel pitch of the display device. picture This occurs when the image scale is approximately equal to the pixel pitch that matches the image scale.

[0005] The image-side image scale β' is defined as the ratio of the extent s of an object on the display image to the extent s' of the image of that object on the camera's sensor. TIFF0007632913000001.tif12146

[0006] Moiré is caused by special measurement arrangements, in particular those that map exactly one display pixel to exactly one (or a fixed integer number) sensor pixel. If so,However, these measurement arrangements are difficult to realize in practice due to the image distortion caused by the camera lens and the required precise alignment between the camera and the display device.

[0007] Furthermore, it is known from documents JP2008-035241A, US7705883B2 and EP2097783A1 that Moiré interference can be reduced by moving at least one optical element, for example the sensor of the camera, relative to other elements in the camera. Document US7705883B2 describes an apparatus and method for suppressing aliasing or Moiré interference using a camera shake correction unit. In an exemplary embodiment, the method comprises sensing the movement of the camera and acquisition sensing the image; and moving at least one optical element in the camera during exposure of the image. Stabilize the image 、 Suppress aliasing or moire interference in images 。

[0008] In such a method, the optical elements relative to the sensor in the camera Relative The movement is adjusted to the pixel pitch of the sensor. And On the order of the Nyquist frequency of the sensor pixel To be carried out .

[0009] It is also known that Moire interference can be mitigated or avoided by optical defocusing, i.e. by causing the camera lens to capture the displayed image slightly out of focus on the camera sensor. However, this reduces the effective spatial resolution of the camera image. Aliasing errors are A mistake occurred Very low spatial frequencies (spatial frequencies much lower than the Nyquist spatial frequency determined by the camera sensor) and However, optical defocus appears By Difficult to detect and often Can't be avoided or Completely avoided I can't However, the occurrence and location of such aliasing errors (i.e., their allocation in the camera frequency space) wasThe spatial frequency (Frequency) depends not only on the pixel pitch of the sensor pixels but also on the pixel pitch of the display pixels. The occurrence and location of such aliasing errors are The pixel pitch ratio of the display device and the camera Depends .

[0010] in general, The aliasing error is The pixel pitch of the camera's sensor pixels and the pixel pitch of the display pixels and Ratio of (camera magnification (magnification) in correction It was , called the Reproducibility Scale (RPS), is in the range greater than 1 and less than 2. Special However, in principle, RPS Less than 1 or 1 or more Even though, For example, RPS but 3 or 4 、 Aliasing errors are possible.

[0011] The pixel pitch of the camera sensor pixel is D S , the pixel pitch of the display pixels is D A Then, the RPS is given as follows: TIFF0007632913000002.tif12150

[0012] Aliasing errors are also affected by the shape and apertures of the display pixels. For example, a display device in which square display pixels are arranged at equal intervals vertically and horizontally will generate different moire interference than a display device with rectangular display pixels, even if it has the same display pixel pitch. Also, if the display pixel pitch in the vertical direction (column direction) is different from the display pixel pitch in the horizontal direction (row direction), different moire interference may occur. For this reason, table Display device Specialized What is needed is a method for correcting Moire interference.

[0013] The reduction of moire interference, similar to the defocusing process, Smoothing filteringLow-pass filters are known for filtering the camera image in position space, but such smoothing also causes a loss of effective spatial resolution and cannot reliably suppress very low aliased spatial frequencies.

[0014] Furthermore, it is possible to convert the camera image into frequency space, for example by a two-dimensional discrete Fourier transform, and to remove or suppress spurious frequency components that occur in frequency space due to aliasing. Ning By inversely transforming the frequency space representation into a position space where moire interference is suppressed, The image that was scanned However, this method does not remove spurious frequency components (due to aliasing) whose frequency and intensity are indistinguishable from spatial frequencies that may actually exist. For example, workman Illusory Very low The spatial frequency is ( Uniform In contrast, the luminance distribution of the reflected light is such that the reflected light cannot or only imperfectly distinguishes between correctly recorded spatial frequencies caused by the locally non-uniform luminance of a display (driven by a fixed angle).

[0015] From JP3755375B2 a method is known for suppressing moiré interference in camera images taken by an electronic display. In this method, a number of camera images are recorded by a camera. Between the recording of the individual camera images, the camera returns to the starting position at which the first camera image was taken. Based on , for the display Tare Vertically (i.e., along columns of the display pixels arranged in a matrix) and / or horizontally (i.e., along rows of the display pixels arranged in a matrix) offset Be , the offset in each direction is half the pixel pitch of the electronic display is .

[0016] From the individual camera images thus captured, a moire-corrected resultant image is generated by averaging.

[0017] In addition, US6,831,995B1 describes multiple n 2 Camera images acquisition Each camera image is a single camera image. At the time of acquisition Between each solid fixed Acquired It is disclosed that the images are taken at positions. The image taking positions are arranged in a staggered grid pattern in a square or rectangle whose vertical / horizontal range is equal to the vertical / horizontal display pixel pitch. In US6,831,995B1, it is proposed to generate a composite image by oversampling n times from these multiple camera images, and to reduce or eliminate the moire interference therein by performing sliding averaging.

[0018] Document JP2014-174803A describes a method for removing moiré noise from an image by performing a two-dimensional Fourier transform and extracting frequency components associated with low spatial frequencies, while removing other frequency components associated with relatively high spatial frequencies. The Fourier transform thus modified is then transformed back into the spatial domain.

[0019] Document WO2018 / 146765A1 describes a method for suppressing moiré without affecting image resolution: From a first defocused image, frequency components associated with low spatial frequencies are extracted in the Fourier domain; from a second, non-defocused image, frequency components associated with high spatial frequencies are extracted in the Fourier domain; the extracted frequency components from the first and second images are combined and transformed back into the spatial domain.

[0020] It is an object of the present invention to provide an improved method for suppressing aliasing errors in a resultant moiré corrected image formed from at least one camera image. Summary of the Invention

[0021] According to the invention, this object is achieved by a method having the features of claim 1.

[0022] It is a further object of the present invention to provide an improved method for assessing the display quality of a pixel-based display device.

[0023] According to the invention, this object is achieved by a method having the features of claim 11.

[0024] Furthermore, it is an object of the invention to provide an apparatus for carrying out one of these methods.

[0025] This object is achieved according to the invention by a device having the features of claim 14.

[0026] Advantageous embodiments of the invention are the subject matter of the dependent claims.

[0027] In a method for suppressing aliasing errors, a moire corrected result image is formed from at least one camera image. The at least one camera image includes: Imaging optics System and Se a sensor surface having sensor pixels; Camera with The image is captured as an image of the display image by do. The display image is formed on a display device having display pixels arranged in a matrix. Use the camera The image is formed on the sensor surface. The display pixels are Spaced apart The display pixel pitch is the distance from the center of one display pixel to the center of the nearest other display pixel.

[0028] In accordance with the present invention, the camera is moved relative to the display device along at least one offset path while capturing at least one camera image. Sera can be.

[0029] Camera image Acquisition time The camera moves relative to the display device for 0≦t≦T. Forced to When you press imaginary point or Actual points , e.g., near the center Located Center of display pixel 、The projection onto the camera's sensor plane generally varies.

[0030] This is a time-dependent trajectory that follows the camera movement. JPEG0007632913000003.jpg14163 is called the offset path, and x0, y0 are the x and y coordinates of the camera at the start of recording the camera image. Represents , on the other hand, δ x (t), δ y (t) during exposure raw Displacement in x and y directions Represents .

[0031] The coordinates x, y are displayed on the display. Fixedly It is specified relative to the selected coordinate system.

[0032] Such an offset path length is JPEG0007632913000004.jpg15163 is called the offset.

[0033] The offset can be achieved by moving the camera and / or the display relative to the world coordinate system, which is independent of the camera and the display. That is, the x, y coordinate system related to the display may be stationary relative to the world coordinate system, or it may be movable as well. In the description of the offset path, only the relative movement between the camera and the display is important. Therefore, in the following, "camera movement" always means the relative movement with respect to the display, "Camera movement" is It may also be achieved partially or completely by translation of the display device relative to the world coordinate system.

[0034] Preferably, when the camera is moved, the CameraThe orientation is approximately maintained. However, it is known to those skilled in the art that panning a camera or display by a very small panning angle α, where the approximation sin(α)≈α applies, is essentially equivalent to a translation. Therefore, if the distance between the camera and the display is large enough, the offset can be eliminated by panning the camera or display. Give rise to It is also possible.

[0035] The display device has a display pixel in the plane of the sensor surface. Opening degree and the imaging optics of the camera System and (where x', y' are two mutually orthogonal coordinates in the plane of the sensor surface). This luminance distribution is (over the entire plane of the sensor face) Two-dimensional sensitivity distribution function s(x', y') of a sensor pixel To Therefore, the sensor pixel Opening degree Depends on Captured do.

[0036] The two-dimensional gray-scale distribution function g(x', y') of the camera image over the entire continuous spatial coordinates x', y' in the sensor area is given by Cameras and Displays and are relatively fixed in position, Shine The sensitivity distribution function s(x', y') is calculated for each point of the intensity distribution l(x', y'). in By multiplying 、 It is possible to identify. JPEG0007632913000005.jpg9163

[0037] This gradation value distribution function is Across By integrating, the signal value of the sensor pixel is obtained. This is the convolution of the luminance distribution and pixel sensitivity. , then It can be expressed as sampling at the positions of the sensor pixels. In particular, when the pitch of the display pixels and the pixel pitch of the sensor pixels are the same or similar in size, This sampling By , Mo It is known that array interference occurs.

[0038] By moving the camera during the exposure of one camera image at time 0≦t≦T, a point in the displayed image is mapped to multiple points in the sensor plane, the sum of which can be viewed as the motion-induced point spread function (PSF) h(x', y').

[0039] For example, if we map only Δx in the x' direction, Ping A camera that provides uniform linear motion of a point Movement (Due to translation or very small panning angles P For the running test, the point response is Next It will look like this. JPEG0007632913000006.jpg17163

[0040] Therefore, the correction in the sensor area of ​​the camera was done The tone distribution function g'(x', y') is Attributable to P Convolution with SF To This can be calculated as follows: JPEG0007632913000007.jpg14163

[0041] Movement Attributable to P The Fourier transform H(ωx', ωy') of SF generally exhibits low-pass characteristics, but this depends on the spatial course as well as the length of the offset path. For example, if there is an offset only in the (horizontal) x direction, only high horizontal spatial frequencies are attenuated. Whereas, High vertical spatial frequencies are not attenuated.

[0042] Surprisingly, the camera is Relatively (offset path) to shift the camera image relative to the display image. Relatively It has been found that by shifting, moiré interference is reduced or even eliminated, without the drawback of a significant decrease in effective spatial resolution in the resulting moiré-corrected image known from the prior art.

[0043] Offset, i.e. the position of the camera relative to the display Relatively move vinegarThe length of the trace is It is almost the same size as It has been found to be particularly advantageous to select an offset path such that the displayed image is more clearly visible. , especially decomposed into display pixels, death Review It is possible to evaluate do.

[0044] Furthermore, the method of the present invention can be used to prevent, for example, unevenness on a display device. one N Brightness Low spatial frequencies in the displayed image that are due to the distribution are preserved. In contrast, low spatial frequencies that are erroneously caused by aliasing are reduced or eliminated by the method.

[0045] Another advantage of the method according to the invention is that it is possible to reduce the number of moving elements in the camera, e.g. the sensor chip, Relatively This can be done without moving optics, which makes it easier to calibrate the cameras, especially the luminance measuring cameras.

[0046] Further advantages of the method according to the invention are Camera movements that help reduce moire interference Without considering the image scale β', Also , sensor pixel pitch too Without considering, table The display pixel pitch is the only factor to determine too However, this is possible in embodiments where the imaging scale β′ and / or the sensor pixel pitch are additionally used, i.e. to reduce the Moire interference. suppression system Further improve This is not intended to exclude embodiments for which

[0047] In the method according to the invention, in particular a small number of individually recorded camera images Using , Moire correction (or suppression of aliasing errors) can be Preferably, the moiré correction is performed using one recorded camera image. This is because the moiré correction is performed using one recorded camera image. Brightness Due to the low light intensity, the camera requires a long exposure time to record the image. setting If you have to for , a small number of recorded camera images Using this method, measurement time can be significantly reduced.can By point , is particularly advantageous.

[0048] Preferably, the offset path is Maximum of is the display pixel pitch 5 Double below Any offset beyond this will not contribute or will only contribute slightly to the correction of Moire interference, and will not affect the camera image. Not only the spatial resolution of , and the resulting moiré-corrected image space formed therefrom. The resolution is also poor. It is known that...

[0049] In an embodiment of the invention, the moiré corrected result image is formed from a plurality of camera images. By moving the cameras, an offset path is generated for each camera image starting from a respective starting point. Between the first camera image and at least one further camera image, The camera is offset relative to the display, so that a starting point associated with at least one further camera image; The 1 Different from the starting point related to the camera image 。

[0050] The individual camera images are superimposed, i.e. summed or averaged pixel by pixel. Different camera images can be weighted differently in the averaging process. Each camera image can be captured while the camera is offset from the display by at least one offset. Also, At least one of the multiple camera images the acquisition Without moving the camera relative to the display during the exposure, To be acquired thing too can.

[0051] By forming a moiré-corrected result image from multiple camera images, Since the offset path associated with a single camera image in each case can have a shorter length (smaller offset), Mo The advantage is that the resulting image, which has been corrected for distortion, has a particularly high spatial resolution. Obtained .

[0052] Another advantage of this embodiment is that the display device Brightness The advantage of this is that even with exposure times that have to be chosen very short due to the sensitivity of the camera, a large number of different offset paths can be approached. Mo Suppress that Better can be achieved.

[0053] The present invention one In an embodiment, a first camera image, a second camera image and at least a third or further camera image are recorded.

[0054] The first camera image and the second camera image are displayed by the same display device Structurally identical images are captured R The third camera image is structurally identical to the first and second camera images but is captured on a different display device. Taken from R hand Good too.

[0055] Structurally identical display images are those whose frequency characteristics do not differ, or differ only insignificantly. Display images that have the same allocation of display pixels are structurally identical.

[0056] However, the gray values ​​( Brightness value) small change For example, even if the gray value changes by a maximum of 1% of all display pixels, the first camera image and the second camera image according to the method of this embodiment can be usefulness Such Changed It is understood that the displayed images are also structurally identical.

[0057] Similarly, all or a large number of display pixels between the recording of the first camera image and the recording of the second camera image may be Uniform A small change, e.g., adding or subtracting a very small value compared to the average gray value of both displayed images and / or a factor close to 1. all Gray value of of scaling Things to do are the first and second camera images for this embodiment of the method. Do not damage. Display images modified in this way are also understood to have the same structure.

[0058] In general, the two display images are Seki Sequential camera images resulting If the difference is in each case significantly smaller than the Moiré interference imposed on the camera image, they will be considered structurally identical. To determine the difference between the camera images (caused by the modified display image or the imposed Moiré interference), for example, the mean square deviation and / or the maximum deviation in both pixel space and spatial frequency space can be used. In particular, a relative difference of 5% or less shall be understood to be small.

[0059] During recording of the first camera image and at least one third Camera image or further camera footage is being recorded too The camera is not moved or is only moved slightly relative to the display device. "Moved slightly" is intended to mean a camera movement that results in a change in position that is significantly smaller than the display pixel pitch, preferably less than one third of the display pixel pitch. In particular, "moved slightly" means a camera movement that results in a change in position that is significantly smaller than the display pixel pitch, preferably less than one third of the display pixel pitch. R " is an intentionally caused R rather, the relative movement between the camera and the display, e.g. as a result of unavoidable vibrations. It brings This should be understood as a move to

[0060] During recording of the second camera image, the camera is moved relative to the display device along at least one offset path as described with reference to the previously described embodiments.

[0061] A two-dimensional Fourier transform is determined for the first and second camera images and their magnitude profiles (amplitude spectra) are determined as first and second magnitude profiles, respectively. Preferably, the Fourier transform is determined as a discrete Fourier transform for discrete (vertical and horizontal) spatial frequencies or wavenumbers.

[0062] The magnitude response of the offset filter is determined from the first and second magnitude responses. O The offset filter is A fictitious linear, time-invariant system, Gives the output the image of the second camera recorded with an offset or the image of the first camera recorded without an offset but Given the input Be Approximate it when . amplitude The response shows the magnitude response of the transfer function of such an offset filter.

[0063] The Fourier transform is At least one third Camera image Or for further camera images, each The magnitude response of the offset filter is determined for each case. and It is multiplied. from , i.e. at least one third Camera image Or further Fourier transform and amplitude response of the camera image and Product of from After the moiré correction, the image is inverse Fourier transformed ( Inverse Fourier transform ) By each In case Decision It is determined.

[0064] Determined from the first and second camera images , which approximately describes (restricted to linear and time-invariant systems) the effect of offset motion on the second camera image For the third or further camera images by applying the magnitude response too , and Moire interference can be suppressed in a similar manner as for the second camera image. Can The advantage of this embodiment is that there is no need to move the camera (relative to the display device) when taking the third and subsequent camera images.

[0065] This allows moiré correction even for camera images with very short exposure times (e.g. when capturing very bright displays) and avoids mechanical stresses that the camera and / or display may be subjected to during movement along the offset path.

[0066] In a further aspect of this embodiment, the first and second camera images are captured from a first display device and a third display device. Camera image Or a further camera image is captured from a second or further display device. do. The second or further display device is of identical construction to the first display device and is positioned relative to the camera in the same or a similar recording orientation.

[0067] A similar recording arrangement is defined as a set of the same measurement devices with geometric deviations that are customary for the arrangement of measurement objects and / or measuring devices within the scope of production or quality control of such display devices. measurement Means the placement of a second or further identical display device within the setup.

[0068] Same Measurement setup to at least one further structurally identical display device in do, Derived amplitude response based on the first display device of Applicable What to do , for applying moiré correction On the occasion , in each case Leave, No movement mosquito Or capture only one camera image with slight movement It is said that It has the advantage By , further reducing both the mechanical load and the required measurement time. This means: especially, The measurement setup is configured once based on the first display device and then, e.g. In a continuous process of production and quality control, Mr. It can be applied to various display devices without modification.

[0069] one In an embodiment, the magnitude response of the offset filter is calculated as a first magnitude response (from the Fourier transform of the first camera image) Decided ) to the second magnitude response (obtained from the Fourier transform of the second camera image Decided ) In this way, the magnitude response of the offset filter can be determined in a particularly simple manner.

[0070] In a further embodiment, the offset filter comprises: No. 1 Magnitude Response Second magnitude response toIt can be formed by subjecting the quotient of to a non-linear transformation, for example binarization.

[0071] In such an embodiment, the amplitude response of the offset filter is determined from a first magnitude response (determined from a Fourier transform of the first camera image). Ta ) is used to segment the magnitude curves by a local segmentation algorithm based on the quotient of the second magnitude response to a given threshold. less than If the quotient of the magnitude curve is greater than or equal to this predetermined threshold, the image is binarized by assigning the value 0 to each pair of vertical and horizontal spatial frequencies. To is assigned the value 1.

[0072] In this way, a particularly stable offset filter can be determined. Moreover, the stability of such an amplitude response, expressed as a binary filter, can be further improved by applying further image operations, such as morphological operators.

[0073] Such an offset filter would allow the camera to be offset during recording of the second camera image (recorded from the first display device) while maintaining the other process steps already described. Move Alternatively, it can also be determined by the fact that only the sensor with the sensor pixels arranged in a matrix is ​​moved relative to the display device, while the camera is stationary relative to the recorded display device. That is, in the camera, the sensor is moved relative to the camera housing during the recording of the second camera image, for example by a piezo actuator. This can reduce the mechanical stress on the camera. This can also reduce the device-related effort for determining the offset filter, since cameras are available that already incorporate the appropriate actuator technology for moving the sensor.

[0074] The method one In an embodiment, a teach-in step is performed prior to the recording of at least one camera image to obtain a moiré-corrected result image. Steps) Moire interference The measurement value is At least one preferred offset path is determined that aligns the display device and the camera such that a predefined moiré threshold is below and / or minimized.

[0075] The determination of the at least one preferred offset path may be performed by selecting the parameters thereof as parameters of a discrete optimization problem, and the Moire interference may be reduced. The measurements are , is selected as the optimization criterion to be minimized, for which a statistical estimate is determined based on a sample of the resulting moiré-corrected image.

[0076] In each case, the moiré-corrected result image on which this estimate is based is formed from the camera image using the method according to the invention. The measurements are Each offset path is inspected using a teach-in step as a quality criterion. Steps ) In It is decided.

[0077] Product Quality Standards (Assigned Moire Interferometry The procedure can be stopped if at least one favorable offset path is found such that ) is below a predefined Moiré threshold. Alternatively, place A fixed number of optimization steps In the If not achieved or sufficient, the method ends.Methods for solving such discrete optimization problems are known from the prior art.

[0078] For example, a preferred offset path may be multiple straight lines of the camera relative to the display. move may be determined by varying the direction and length (offset).

[0079] Similarly, the preferred offset path is a set of straight lines that vary in direction and length (offset). move may be determined as a polygonal path from

[0080] In addition, a randomly selected offset path is performed during the teach-in step to reduce Moiré interference. Measurements It is also possible to determine multiple preferred offset paths by examining the effect on , where the length (offset) varies randomly but is chosen to be smaller than the offset amplitude. In this way, the offset amplitude, i.e., the maximum length of the offset path, but decision and provides particularly good reduction of Moire interference measurements. Can R .

[0081] Moire interferometry using discrete optimization methods known to those skilled in the art Value Good enough To Or optimal To decrease to make Parameters can be determined that indicate a single preferred offset path. These parameters are also Multiple preferred offset paths are indicated by characteristics such as length (offset), length range (offset interval), or direction. designation You may do so.

[0082] For example, during the teach-in step, the length (offset) and direction can be changed during the recording of at least one camera image. Without to be crossed single A preferred offset path can be determined.

[0083] Furthermore, the offset path teeth, Random selection in spatial direction Be , can be scaled to a length (offset) determined to be preferred.

[0084] An advantage of the embodiment with a teach-in step is that optimal or sufficiently good moiré suppression can be achieved for a selected arrangement of display device and camera.

[0085] After the teach-in step in each case InThe camera image is offset relative to the display image along the determined preferred offset path. Relatively The camera is moved while the camera images are being recorded so that the camera moves. Also, random deviations from the preferred offset path are detected by the camera. move It is also possible to vary the preferred offset path probabilistically by applying

[0086] Depending on the arrangement of display pixels, differently oriented offset paths may suppress Moire interference to different degrees. For example, pixels that are adjacent to each other in the horizontal (x) direction but spaced apart in the vertical (y) direction may Arranged For a display device having rectangular display pixels, mainly vertical direction of It may be advantageous to select an offset path.

[0087] This embodiment therefore allows for the selection of offset paths tailored to a particular display device for particularly good suppression of Moire interference.

[0088] The method one In an embodiment, During recording of at least one camera image, An offset path having an offset less than or equal to the offset amplitude A Mela but When moving, the Moire interference measurement is less than Teach-in steps to minimize and / or In , offset amplitude suitable for display device and camera but decision Will be During the recording of at least one camera image, an offset path is traversed which is randomly selected with respect to direction, course and offset length, the offset length being smaller than or equal to the offset amplitude determined in the teach-in step. too are chosen to be equal.

[0089] one In an embodiment, when the camera is offset along the offset path by a preferred offset relative to the starting position during recording of at least one camera image. Moire Interferometry A preferred offset is determined in a teach-in step such that .function..times ... Moire Interferometry To minimize , discrete optimization methods can be used, as described above.

[0090] After the teach-in step, the camera is moved during recording of the camera image such that the camera image is shifted relative to the display image along an offset path whose length (offset) is within the offset interval determined in each case in the teach-in step.

[0091] In this embodiment, it is sufficient that the optimal or preferred offset path length is adjusted as one parameter for the display and camera combination in the teach-in step.

[0092] It turns out that the offset path of the camera relative to the display device, for which particularly good results of the moiré correction can be achieved, essentially depends on the pixel pitch of the display device and also on the pixel pitch and image scale of the sensor pixels. Therefore, with this embodiment of the teach-in step, a particularly efficient moiré reduction adapted to the respective arrangement of the camera and the display device is possible.

[0093] The determination of the offset path or the offset interval or the preferred offset in the teach-in step can in each case also be performed with reference to a section of the camera image, i.e. a continuous area of ​​sensor pixels.

[0094] For example, for curved displays or , camera lens distortion or , or perspective distortion Due to It has been found that different offset paths, different offset intervals or different preferred offsets are particularly suitable for moiré correction for different regions of the camera image. It may become clear .

[0095] In this embodiment of the method, the relevant parameters of the camera movement (offset path, offset interval or preferred offset) are determined in each case by discrete optimization in a teach-in step for different camera image regions completely covering the entire camera image. Then at least one camera image is recorded for each camera image region, whereby the camera is moved according to the respective assigned parameters. The majority of the camera images thus captured are aligned by an image registration process and then summed or averaged pixel by pixel to form a moiré-corrected result image.

[0096] In this way, the geometric or optical arrangement of the display device will not affect the movement of the camera relative to the displayed image on the camera image. image To give influence Even if the difference is different in different areas of the camera image, As a result, an image with excellent moire correction can be obtained.

[0097] one In an embodiment, a coefficient of variation of sensor pixel values ​​obtained from at least one region of a camera image is Moire Interferometry The coefficient of variation, i.e. the spread about the expectation value, can be particularly easily and quickly determined and represents a good approximation of the effects of Moire interference.

[0098] In one embodiment of the method, the offset path is determined probabilistically. The offset path can be determined probabilistically by determining its length, i.e., the offset traveled, as a random variable uniformly distributed in a length interval (offset interval). The offset path is pre-determined with respect to its spatial path. Also to , or randomly determined You can also , like this do The length is scaled according to the determined length.

[0099] In this way, particularly good suppression of Moire interference is achieved for a number of offset movements which are performed independently according to this uniform distribution.

[0100] It is also possible to determine the offset path probabilistically by applying probabilistic deviations to a preferred offset path, e.g. an offset path determined in a teach-in step.

[0101] In an embodiment of the invention, the camera movement relative to the display device is along the column and / or row direction of the matrix of display pixels, i.e. the camera movement is parallel to the display device in the case of a flat display device. In the case of a curved display device, the camera movement is coplanar to a tangent plane, preferably a tangent plane passing through a display pixel located at or near the center of the matrix of display pixels. Such a two-dimensional Within the plane By means of the offset movement, particularly good suppression of Moire interference can be achieved.

[0102] Also, for a curved display device, several different tangential planes can be selected, and for each tangential plane, a respective translation of the camera is performed during the recording of at least one camera image, and the individual camera images are aligned by an image registration process and then summed or averaged pixel by pixel to form a moiré-corrected result image, which allows a particularly accurate moiré correction.

[0103] In one embodiment of the method, the camera is moved along its optical axis relative to the display device. This results in defocus, i.e., convolution with a concentric PSF that slopes towards the edge.

[0104] This embodiment provides displacement along only one direction of movement. Just fine Such a method has the advantage that it can be performed in multiple directions. hand Displacement Do More than but It's easy.

[0105] The method oneIn an embodiment, the camera is moved around the starting position along an offset path that consists of sub-paths that are symmetrical about the starting position, i.e., sub-paths of equal magnitude and direction but opposite direction. For example, the offset path may be mirror symmetric. TIFF0007632913000008.tif48149

[0106] This ensures that the moiré-corrected result image is aligned to the starting position with particularly small deviations. Associated That Become possible .

[0107] In one embodiment of the method, a color filter is placed between the display and the camera sensor, Multiple A color channel-related result image is determined for a number of color channels, a color channel-related offset interval is determined for each color channel, and the color channel-related result images are spaced apart from one another. Alignment will be done.

[0108] Such color filters have different thicknesses and different refractive indices. There may be , Display Devices and Sensors surface The camera lens is placed between the camera and the camera lens, and is arranged almost perpendicular to the optical axis of the camera lens. luminous flux In the case of , the color filters may cause translations of different magnitudes. luminous flux If , then depending on the position (within the sensor area) different It may cause distortion.

[0109] In the proposed embodiment, a moiré-corrected color image can be obtained by overlaying the resultant images associated with the registered color channels. table Inspection related to the spectrum or at least the color channels of the display device too It becomes possible.

[0110] A method for assessing the display quality of a pixel-based display device, comprising: determining from at least one camera image recorded by a camera, according to any of the methods described above; 、 A resultant image after the moire correction is obtained, and the display quality of the display device is judged based on the resultant image after the moire correction.

[0111] The advantages of this method are: Due to Moire interference, Display device quality evaluation shadow Echoes and distortions death This allows for an evaluation that reflects the actual quality of the display device. Moreover, the elimination of aliasing artifacts with high spatial frequencies (close to the Nyquist frequency) allows an unbiased evaluation at particularly high spatial resolution, preferably accurate to one display pixel. As a result, localized variations on the display device can be reduced. N Small defects or abnormality In particular, it is possible to prevent erroneous detection of pixel defects, and thus it is possible to perform evaluation of a display device with particularly high reliability.

[0112] In an embodiment of the method, defective display pixels of a display device are detected and / or localization This makes it particularly easy to carry out a quality control of the display device.

[0113] one In the embodiment, Brightness The uniformity of the distribution is determined. Brightness Uniformity of distribution error or Disturbance The advantage of this technique is that aliasing artifacts with low spatial frequencies, which mimic those of the prior art, are eliminated.

[0114] In particular, the evaluation method according to the invention is useful in the case of pixel-related differences in operating time or intensity statistics between display pixels that arise due to manufacturing techniques and / or aging. Brightness This allows a method known as DeMURA to correct for the differences.

[0115] Preferably, Brightness The difference is, Review Valued 、 and / or 、 Such Brightness The parameter to correct the difference is Based on a displayed image with low brightness or luminance It is decided.

[0116] In one embodiment of the method, to assess the display quality, Photometry The local distribution of a parameter, preferably luminance, is determined, which allows a particularly accurate and objectively reproducible evaluation of the display device.

[0117] An apparatus for implementing one of the above-mentioned methods comprises a camera, a positioning unit, a control unit and an evaluation unit. The positioning unit is arranged to position the camera relative to the display device. Fixed The positioning unit can be designed to move the camera relative to the camera. Fixed and set the display to move. too can.

[0118] The positioning unit is adapted to electrically move the camera or the display device by an offset within the offset interval. composition The control unit is configured to start recording the camera image by the camera. composition will be done.

[0119] The evaluation unit is adapted to generate a moiré-corrected result image using one of the methods described above. composition will be done.

[0120] The advantages of this device result from the advantages of the method described above.

[0121] The positioning unit may be arranged for stochastic or quasi-stochastic movement of the camera independent of the recording of the camera images.

[0122] However, in an embodiment of the present invention, the control unit can also be set to control the positioning unit and trigger the recording of the camera images accordingly, i.e. according to the movement of the camera by the positioning unit, so that the offset path can be reproduced and the filter effect for suppressing Moire interference can be set more accurately.

[0123] In one embodiment of the device, the control unit and the evaluation unit are combined in one control and evaluation unit. This allows a particularly compact design and the use of low-cost and flexible components. For example, the control and evaluation unit can be designed as a PC (personal computer) or a notebook.

[0124] In one embodiment, the positioning unit is designed as a goniometer, which is preferably set to rotate the camera about two mutually perpendicular rotation axes. Goniometers are commonly used positioning units for luminance measurements, which are readily available and particularly cost-effective in this field of application. set up This makes it possible.

[0125] Preferably, the goniometer is set to precisely rotate the camera or display through a very small angle, preferably less than 1 degree, and most preferably less than 1 arc minute. For such very small angles of rotation, a sufficient distance between the display and the camera is required. long Given the distance, a nearly coplanar offset of the display image relative to the camera image is achieved by rotation with the goniometer.

[0126] However, the positioning unit can also be designed as any other movement unit which can be linearly displaced by a motor along at least one, preferably at least two mutually orthogonal movement directions.

[0127] As an example, the positioning unit can be designed as an industrial robot. This allows for particularly flexible movement of the display device or camera.

[0128] The positioning unit can also be designed as a cross table (XY table) which can be moved along two axes. The movement along the axes can be achieved by electrically operated rotary and / or linear drives. For example, a spindle-driven rotary motor can be used for the crossing. Also, piezo-based linear drives can be used.

[0129] In an embodiment of the device, the positioning unit is designed as at least one vibration unit arranged on the housing of the camera and which can be set in a vibration state, by means of which the camera is set in a vibration state during the recording of the camera image, the camera vibration being manifested as an offset path of the camera image relative to the display image.

[0130] It is also possible to arrange several vibration units on the camera, for example one vibration unit each in the horizontal X direction (sensor pixel row direction), the vertical Y direction (sensor pixel column direction) and one vibration unit in the optical axis direction of the camera, which allows a particularly flexible design of the offset path.

[0131] Such a vibration unit can be designed, for example, as a piezo actuator or as a speaker or as a vibration motor and arranged on the camera housing.

[0132] In embodiments using loudspeakers, at least one loudspeaker may be driven with a harmonic drive signal. For such embodiments, the teach-in step may include, for example, determining the frequency and / or amplitude of the drive signal such that the Moiré interference level is particularly well reduced.

[0133] one In an embodiment, the camera is designed as a luminance measuring camera, Photometry parameters, preferably by a display device of the emitted light It is set up to record the spatial distribution of luminance, which allows a particularly accurate and objectively reproducible evaluation of the display device. [Brief description of the drawings]

[0134] Exemplary embodiments of the invention will now be described in more detail with reference to the drawings. [Figure 1] FIG. 2 is a diagram showing a schematic arrangement for capturing a display image of a display device. [Figure 2A] FIG. 2 is a diagram illustrating an arrangement of sensor pixels and display pixels. [Figure 2B] FIG. 2 is a diagram illustrating an arrangement of sensor pixels and display pixels. [Figure 3A] FIG. 4 is a diagram illustrating the magnitude of the Fourier transform of the first and second camera images. [Figure 3B] FIG. 4 is a diagram illustrating the magnitude of the Fourier transform of the first and second camera images. [Figure 4] FIG. 10 is a diagram illustrating a magnitude response of an offset filter. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0135] Corresponding parts are given the same reference numbers in all figures.

[0136] Figure 1 shows table The display device 2 displays the display image By Camera 1 The display device 2 comprises a number of display pixels 2.1 arranged in a matrix along rows 2.3 and columns 2.2. The rows 2.3 extend approximately parallel to a horizontal X-direction. The columns 2.2 extend approximately parallel to a vertical Y-direction.

[0137] Camera 1 is Sensor surface 1.2 is arranged in a matrix. Sensor pixel count 1.3 It is equipped with In front of the sensor surface 1.2, a display image represented by display pixels 2.1 is projected onto the sensor surface 1.2. Imaging The camera lens 1.1 arrangementThe optical axis O of the camera 1 is directed toward the center and is approximately perpendicular to the plane described by the display pixels 2.1. Be is.

[0138] Camera 1 teeth , ( The camera comprises a camera lens 1.1 and a sensor surface 1.2 having sensor pixels 1.3. Ta ) The whole , For example, clamped or screwed into position. The positioning unit 3 is arranged on a holding plate 3.2. The positioning unit 3 is connected to a motor 3.1. To Therefore 、 It is set up to electrically move the holding plate 3.2 along the horizontal x-direction and the vertical y-direction. Instead of a motor, other Transportation , e.g., a piezoelectric actuator etc. can also be used for linear translation along the x and y directions.

[0139] Positioning unit 3 To Therefore, Camera 1 Along the offset path VP 、 Only offset V for display device 2 Transfer The offset V is the length of the offset path VP. It is.

[0140] During recording of the camera image formed by the sensor values ​​read out from the sensor pixel 1.3, the camera 1 Display device The motor 3.1 and the image recording by the camera 1 are controlled by a control unit 4 connected thereto, so as to offset the position 2 in the x-direction and / or y-direction.

[0141] It is also possible to capture multiple camera images while the camera 1 is offset relative to the display device 2.

[0142] The camera image is Review Value unit 5 In this case, camera 1 Multiple camera images are recorded while camera 1 is moving. andThe individual camera images are then superimposed, for example added or averaged, by the evaluation unit 5 to form a Moiré-corrected result image.

[0143] Figures 2A and 2B show diagrammatically the change in position of the display pixels 2.1 relative to the sensor pixels 1.3 when the camera 1 is moved relative to the display device 2. For greater clarity, only a portion of the display pixels 2.1 arranged in a matrix and a portion of the sensor pixels 1.3 arranged in a matrix are shown in each case.

[0144] Sensor pixel 1.3 is sensor pixel pitch D S in For simplicity, the sensor pixel pitch D S is chosen to be the same in the vertical y' and horizontal x' directions, although different distances in the vertical and horizontal directions are possible.

[0145] Similarly, the display pixel 2.1 has a display pixel pitch D A in If the reproduction scale β' achieved by the camera lens 1.1 deviates from 1, the display pixels 2.1 are spaced apart by the sensor pixel pitch D S Compare So, By the reproduction scale of extension or shortening In particular, the resulting reproduction scale (RPS) makes it more susceptible to aliasing (moiré). Therefore Camera image Which spatial frequencies are not displayed correctly in It is decided.

[0146] Figure 2A shows the position of sensor pixel 1.3 at a starting position S. Figure 2B shows the position of sensor pixel 1.3 after camera 1 has moved along an offset path VP during exposure. The offset path VP has a length called offset V.

[0147] In the projection onto the sensor plane 1.2, the offset path VP appears as an offset path image VP' of length, hereafter referred to as image offset V', taking into account the image side imaging scale β'.

[0148] 2.1 One or more display pixels from Sensor pixel 1.3 (image of the displayed image on the sensor surface) Imaging Be R The intensity is convolved only with the pixel aperture (point spread function PSF) of each sensor pixel 1.3 when the camera 1 is not moving. Ma can be.

[0149] In the spatial frequency domain, this means multiplication of the spectrum of the captured display image of the display device 2 (i.e. the matrix of display pixels 2) by the spectrum of the PSF (modular transfer function MTF). The matrix of all sensor pixels 1.3 means sampling, and in the frequency domain it means multiplication of the spectrum obtained, whereby high frequency components may creep into the fundamental spectrum and aliasing may occur.

[0150] By moving the camera 1, one or more display pixels 2.1 from Sensor pixel count 1.3 Image formed on The brightness (Image of the display image on the sensor) is convolved with the pixel aperture (point spread function PSF) of each sensor pixel 1.3 Ma R ,and, The filter kernel h(x', y') determined by the offset path image VP' This is further folded into The position curve of the offset path image VP' is the coordinates x'o, y'o of Starting from the starting position S, the movement in the (horizontal) x' direction and the vertical y' direction amount δ x’ (t), δ y’ (t). The filter kernel h(x',y') is determined by the values ​​{δ x’ (t), δ y’ (t)} In , these positions In The image moving speed v(t) is inversely proportional to the image moving speed v(t) relative to the camera image, and is especially important if the image moving speed v(t) is different from 0. Take . So Other locations TIFF0007632913000009.tif8169 、h Apply (x',y' ) = 0.

[0151] In the spatial frequency domain, this therefore corresponds to the spectrum of the displayed image (the matrix of display pixels 2.1) To, PSF spectrum (MTF) and Spectrum of offset path image VP' of Multiplication Things to do means...

[0152] Therefore, by moving camera 1, the PSF of sensor pixel 1.3 is convolved with the offset path image VP'. Ma This results in a Fourier transform and spectral multiplication of the offset path image VP' in the spatial frequency domain, i.e., filtering. 。 In this way, the interference frequency components are eliminated by selecting the offset path image VP' determined by the offset path VP. restraint or possibility of reducing You can get .

[0153] The offset path VP can therefore be used to determine the filter kernel h(x',y') for position continuous filtering, in particular smoothing to remove or suppress Moiré interference in the camera image. By , The offset path VP is The combination of camera 1 and display device 2 is used to measure the moire interference. As much as possible By discrete optimization, the best reduction is achieved. Decision It is possible to determine

[0154] Compared with discrete position filtering of camera images, In the case The advantages are: In principle, At any spatial frequency 、 In particular, the sensor pixel pitch f o =1 / D S, and hence spatially discrete filtering of discretized camera images. So Inaccessible spatial frequencies Even though , spatially continuous with the filter kernel h(x', y') target Filtering to attenuate or eliminate Suruko friend can Therefore, it is possible to suppress the moire interference while maintaining a high spatial resolution.

[0155] A further developed embodiment of the present invention will now be described with reference to FIGS. 3A, 3B and 4. FIG.

[0156] FIG. 3A shows the horizontal and vertical Direction spatial frequency f x’ ,f y’ To Cross No. 1 of Magnitude Plot|X τ1 (f x’ ,f y’ FIG. 1 is a schematic diagram showing of Magnitude Plot|X τ1 (f x’ ,f y’ )| is the first exposure Over time τ exposure First camera image In Fourier transform|X τ1 (f x’ ,f y’ )| Size It is.

[0157] The exposure of the first camera image is performed such that the camera 1 does not move or moves slightly relative to the display device 2 during the first exposure time τ1. Here and below, "moved slightly" refers to the distance between the display pixel pitch D A smaller than, preferably D A / 3. In other words, the offset path VP caused by the movement of the camera 1 relative to the display device 2 is understood to be the movement that causes an offset V smaller than the display pixel pitch D A smaller than, preferably D A1.2 has an offset V parallel to the sensor surface 1.2 that is smaller than / 3.

[0158] The first exposure time τ1 is selected to be very short relative to the moving speed of the camera 1 (i.e., the offset path image VP' is selected to be very short). vinegar The first camera image can be captured by changing the first exposure time τ1, whereby the change in the first exposure time τ1 of the display pixel 2.1 is inversely proportional to the change in the first exposure time τ1. Brightness By increasing the first exposure time τ1, compensate It is possible.

[0159] Additionally or alternatively, the first camera image is captured by reducing or stopping the movement of camera 1 during the first exposure time τ1. of record can be .

[0160] Image offset V' is Relatively very short mosquito or completely suppressed To Thus, the filtering effect of the filter kernel h(x', y') determined by the offset path image VP' described with reference to Figures 2A and 2B is reduced. In the extreme case, when the camera 1 is completely stationary with respect to the display device 2, the filter kernel h(x', y') becomes a Dirac pulse ( Dirac - Impulses To Degenerate, No change occurs in the primary camera image recorded by sensor pixel 1.3. Let do not have.

[0161] Therefore, the Fourier transform of X τ1 (f x’ ,f y’ ) indicates aliasing (i.e., Moiré interference). In FIG. 3A, the light grey values ​​are the Fourier transform X τ1 (f x’ ,f y’ )of Shake The dark grey values ​​indicate a larger width. Fourier Transform X τ1 (f x’ ,f y’ )'s swingThe horizontal dimension of FIG. 3A indicates that the horizontal spatial frequency f x’ , which is related to the horizontal x' direction of the sensor plane 1.2. The vertical dimension of FIG. 3A corresponds to the vertical spatial frequency f y’ which is assigned to the vertical y' direction of the sensor surface 1.2.

[0162] Aliasing (moiré) in the first camera image is Fourier Transform X τ1 (f x’ ,f y’ ) in a certain Horizontal and vertical Direction Spatial Frequency And big Corresponding to the amplitude Vertical line and beside Line shape in, Aware Author To Bright Ku (white Ku ) Bring to light No. 1 Interference Causes M1.

[0163] FIG. 3B is a schematic similar to FIG. method and exposed for the second exposure time τ2. Then, the same display image is acquired as the first camera image and is displayed by the same display device 2. Second camera image In Fourier transform|X τ2 (f x’ ,f y’ )|Second of Magnitude plots are shown. death is.

[0164] The exposure of the second camera image is Unlike the first camera image, the second exposure time τ2 is changed by moving the camera 1 relatively. S An offset path image VP with an offset V parallel to the sensor plane 1.2 is generated. line This offset V is the display pixel pitch D A between 1 and 5 times that of the original, i.e. the second camera image is recorded as already explained with reference to Figures 2A and 2B.

[0165] In addition, the Fourier transform of the second camera image is workman Illiasing (moire) Second Interference M 2 As However, due to the already explained filter effect of the filter kernel h(x', y') determined by the offset path image VP', This second interference M 2 teeth, In the Fourier transform of the first camera image, The second 1 Interference of M This is a significant reduction compared to 1.

[0166] The suppression of aliasing (moiré) achieved in the second camera image with an offset V of camera 1 relative to display device 2 during the second exposure time τ2 can be calculated from a system theory point of view as the transfer function of the offset filter: expression This can be done by taking the Fourier transform of the first camera image X τ1 (f x’ ,f y’ ) (There is no moire suppression offset V) and Fourier transform of the second camera image X τ2 (f x’ ,f y’ )and It results from the quotient of

[0167] In particular, the selective suppression of frequencies due to the offset V during the recording of the second camera image is due to the amplitude response |G τ2 (f x’ ,f y’ )|As expression It is possible.

[0168] For example, the magnitude response |G τ2 (f x’ ,f y’ )| is the ratio of the second magnitude response to the first magnitude response Size It can be calculated from the ratio. JPEG0007632913000010.jpg16163

[0169] Or, the magnitude response |G τ2 (f x’ ,f y’ The determination of || can also be based on local segmentation in the manner of image processing operations. The local segmentation is binary in a way that depends on a threshold. JPEG0007632913000011.jpg7163 Amplitude response | G τ2 (f x’ ,f y’ )|Each Size Assign to a value.

[0170] For example, the image processing operation can be applied to a ratio of the second magnitude to the first magnitude response, so that the amplitude response |G τ2 (f x’ ,f y’ )| is the binary magnitude response JPEG0007632913000012.jpg7163. In general, |X τ1 (f x’ ,f y’ )| and |X τ2 (f x’ ,f y’ )| to the magnitude response |G τ2 (f x’ ,f y’ To derive ||, other operations such as logical and morphological operations from the image processing field and additional operations are used. vinegar For example, the magnitude response |G τ2 (f x’ ,f y’ )|, before forming a quotient in the same or similar manner as τ1 (f x’ ,f y’ )|,|X τ2 (f x’ ,f y’ )| is then binarized and the magnitude response |G τ2 (f x’ ,f y’ )| can be derived.

[0171] in general, The purpose of defining the offset filter is to reduce the magnitude response |Gτ2 (f x’ ,f y’ )|, in which No. 1 of (Unadjusted of ) amplitude Profile|X τ1 (f x’ ,f y’ )| has high amplitude Decision It is determined, and Second of (adjustment was done ) amplitude Profile|X τ2 (f x’ ,f y’ If a relatively very low amplitude is determined in | The set of horizontal and vertical spatial frequencies (f x’ ,f y’ ) with a low amplitude or with zero.

[0172] Figure 4 shows the first and second magnitude responses |X τ1 (f x’ ,f y’ )|,|X τ2 (f x’ ,f y’ )|G τ2 (f x’ ,f y’ )| is a schematic diagram showing the amplitude response |G τ2 (f x’ ,f y’ )| specifies the degree of frequency-selective attenuation (or amplification) that the camera image undergoes for a parameter combination of horizontal and vertical spatial frequencies.

[0173] is a binary magnitude response The application of JPEG0007632913000013.jpg8163 is |X τ1 (f x’ ,f y’ )| and |X τ2 (f x’ ,f y’ )|, all frequency components that differ significantly between |X τ1 (f x’ ,f y’ )| only if it is significantly weaker than the (residual) moire in |X τ2 (f x’ ,f y’ )| can also suppress the (residual) moire that exists in continuous value Magnitude response |G τ2 (f x’ ,f y’ )|Offset filter than It is advantageous do. Furthermore, the binary amplitude response The robustness of this method can be further improved by adding simple morphological operations such as dilation to JPEG0007632913000014.jpg8163.

[0174] By using an offset filter, the offset V during exposure is absolutely It is possible to suppress moiré even in camera images taken with no or only a small offset V. For this purpose, the camera images are Fourier transformed. The Fourier transform of the camera image (X(f x’ ,f y’ ) is the magnitude response |G τ2 (f x’ ,f y’ )| is frequency-selectively multiplied. JPEG0007632913000015.jpg7163

[0175] The spatial frequency weighted Fourier transform X'(f x’ ,f y’ )teeth, A spatial frequency f where a strong first interference M1 is present in the first camera image but no interference M2 or only a small interference M2 is present in the second camera image. x’ ,f y’ Because for these spatial frequencies the magnitude response of the offset filter |G τ2 (f x’ ,f y’ )| is close to zero or is zero. According to the present invention, the spatial frequency weighted Fourier transform X'(fx’ ,f y’ ) is then transformed by the inverse Fourier transform ( Inverse Fourier transform ) and as a result As A moire-corrected resultant image is obtained.

[0176] That is, if the geometrical and essential lighting conditions (relating to the arrangement of the camera 1 and the display device 2) do not change or only change slightly compared to when the first and second camera images were recorded, the amplitude response |G τ2 (f x’ ,f y’ )| is the Fourier transform of the camera image followed by the inverse Fourier transform ( Inverse Fourier transform ) applies to By , the same or similar aliasing (moiré) interference occurs when the camera 1 is moved relative to the display device 2 along the same offset path VP selected when the second camera image was recorded. of Suppression can be achieved.

[0177] This prevents camera 1 from moving while recording images. mosquito Or even just moving it slightly, interference M1, M2 The same or equivalent restraint on In particular, the suppression of vibration offsets can be achieved. operation This makes it possible to avoid mechanical stress on the camera 1 and / or the display device 2, such as that caused by

[0178] Also, it was recorded with a very short exposure time. In order to , enough interference Offset required for suppression operation Even with camera images that cannot be interference In addition, it is possible to suppress further camera images recorded under similar recording conditions, for example, Separate, but Same structure display Suppressing disturbances in camera images from a device too It is possible.

[0179] The third camera image and the other camera images are displayed on a display device 2 different from the first and second camera images. of photograph death For example, display devices 2 that are manufactured identically in series during a production process can be positioned, within normal tolerances for quality control, in the same relative position to camera 1 as the first display device 2 from which the first and second camera images were taken.

[0180] And these One after the other To Replace Display device 2 By using , a third camera image and a further camera image are recorded. Camera image and the moire interference in the further camera images is different but identically configured first of Display device 2 In contrast, Offset filter determined from the first and second camera images of Applicable What is to be done By 、 is eliminated or attenuated.

[0181] Due to the small geometric changes in the recording conditions between the same display devices that are actually expected expensive For robustness, we use the above do is the determined binary magnitude response JPEG0007632913000016.jpg8163, for example, expansion etc. Morphological Processing This allows the processing to be performed as follows: Originally Spatial frequencies in the immediate vicinity of the spatial frequency detected as Moire interference are also suppressed. For example, rotation around the surface normal axis of the display device 2. Slightly changed recording situation To The small amount of aliasing frequencies that occurs Misalignment At least in part To be corrected . [Explanation of symbols]

[0182] 1 Camera 1.1 Imaging optics system, Camera Lens 1.2 Sensor surface 1.3 Sensor pixels 2 Display device 2.1 Display pixels 2.2 columns 2.3 rows 3 Positioning unit 3.1 Motor 3.2 Holding plate 4. Control Unit 5 Evaluation Unit D S Sensor pixel pitch D A Display pixel pitch f x’ ,f y’ Horizontal and vertical spatial frequencies |G τ2 (f x’ ,f y’ )| Magnitude response M1, M2 1st Interference, Second Interference O optical axis S start position V Offset V' Image offset VP offset path VP' offset route image |X τ1 (f x’ ,f y’ )| First Magnitude Plot |X τ2 (f x’ ,f y’ )| Second Magnitude Plot

Claims

1. 1. A method for suppressing aliasing errors in a moiré corrected resultant image formed from at least one camera image, comprising: The at least one camera image is imaged in a matrix by a camera (1) with an imaging optical system (1.1) and a sensor surface (1.2) with sensor pixels (1.3). Ａ ), during the recording of at least one camera image, the camera (1) and / or the sensor surface (1.2) are moved relative to the display device (2) along at least one offset path (VP) starting from a start position (S) assigned to each camera image, and a first camera image, a second camera image and at least a third or further camera image are recorded, the first camera image and the second camera image are recorded as respective images of structurally identical display images displayed by the same display device (2); during the recording of the first camera image and the at least one third or further camera image, the camera (1) is not moved or is only moved slightly relative to the display device (2); During the recording of the second camera image, the camera (1) is moved relative to the display device (2) along at least one offset path (VP); For the first camera image and the second camera image, first and second magnitude responses of the Fourier transform (|X τ１ (f x’ , f y’ )|, |X τ２ (f x’ , f y’ )|) is determined, The amplitude response of the offset filter from the first and second magnitude responses |G τ2 (f x’ ,f y’ ) | is determined, For at least one of the third or further camera images, the Fourier transform is determined in each case and the magnitude response |G τ2 (f x’ , f y’ ) |, which gives us The moiré-corrected image is determined by inverse Fourier transform. A method comprising:

2. The camera (1) is moved relative to the display device (2) along at least one offset path (VP) starting from a start position (S) assigned to each camera image during the recording of at least one camera image.

2. The method of claim 1 .

3. the first camera image and the second camera image are recorded from a first display device (2); Each further camera image is recorded from a further display device (2) which in each case has the same structure as the first display device (2) and is arranged in the same position as the first display device (2) relative to the camera (1).

3. The method according to claim 1 or 2.

4. A binary amplitude response |G τ2 (f x' , f y' )| is obtained by binarization. is calculated, In this case, the magnitude response |G τ2 (f x’ ,f y’ )| is determined as the quotient |G τ2 (f x' , f y' )| of the second magnitude response |X τ2 (f x' , f y' )| to the first magnitude response |X τ1 (f x' , f y' )|, In the binarization, when the quotient |G τ2 (f x' , f y' )| is lower than a predetermined threshold, a value of 0 is set to the binary amplitude response. assigned to When the quotient |G τ2 (f x' , f y' )| is higher than or equal to a predetermined threshold, the value 1 is set to the binary amplitude response. assigned to The method according to any one of claims 1 to 3.

5. The offset (V) along an offset path (VP) parallel to the sensor surface (1.2) is at most the display pixel pitch (D Ａ ) is five times The method according to any one of claims 1 to 4.

6. In a teach-in step, an offset amplitude for matching the display device (2) and the camera (1) is determined such that, during the recording of the at least one camera image, the moiré interference measurement is below a predefined moiré threshold and / or is minimal when the camera (1) moves through an offset path (VP) having an offset (V) less than or equal to the offset amplitude. The method according to any one of claims 1 to 5.

7. In a teach-in step, at least one offset path (VP) for matching the display device (2) and the camera (1) is determined such that, during the recording of the at least one camera image, when the camera (1) moves along this offset path (VP) relative to a start position (S), a Moiré interference measurement is below and / or minimal to a predefined Moiré threshold. The method according to any one of claims 1 to 6.

8. For at least one camera image, the camera (1) is vertically displaced with respect to the display device (2). The method according to any one of claims 1 to 7.

9. At least one camera image is moved relative to the display image along a first offset path (VP) and a second offset path (VP) symmetrically disposed to the first offset path (VP). The method according to any one of claims 1 to 8.

10. A color channel-related result image for a plurality of color channels in each case is determined by arranging a color filter between the display device (2) and the sensor surface (1.2) of the camera (1), a color channel-related offset interval is determined for each color channel, and the plurality of color channel-related result images are superimposed on one another. The method according to any one of claims 1 to 9.

11. A method for evaluating a display quality of a pixel-based display device (2), comprising forming a Moiré-corrected result image from at least one camera image recorded by the camera (1) according to the method of any one of claims 1 to 10, and evaluating the display quality on the basis of the Moiré-corrected result image. A method comprising:

12. Defective display pixels (2.1) of the display device (2) are detected and / or located.

12. The method of claim 11 .

13. A local distribution of photometric parameters across the display device (2) is determined.

13. The method according to claim 11 or 12.

14. The local distribution of luminance over the entire display device (2) is determined.

13. The method of claim 12.

15. An apparatus for carrying out the method according to any one of claims 1 to 14, comprising a camera (1), a positioning unit (3), a control unit (4) and an evaluation unit (5), the positioning unit (3) is configured to move the camera (1) by an offset (V) that is within an offset interval; The control unit (4) is configured to initiate recording of camera images; The evaluation unit (5) is configured to form a moiré-corrected result image from at least one camera image using the method according to any one of claims 1 to 11. An apparatus comprising:

16. The control unit (4) is configured to control the positioning unit (3) and to initiate recording of camera images in a coordinated manner with the movement of the positioning unit (3).

16. The apparatus of claim 15.

17. The control unit (4) and the evaluation unit (5) are each designed as part of a control and evaluation unit.

17. Apparatus according to claim 15 or 16.

18. The positioning unit (3) is designed as a vibration unit and is arranged on the housing of the camera (1). Apparatus according to any one of claims 15 to 17.

19. The camera (1) is designed as a luminance measuring camera. Apparatus according to any one of claims 15 to 18.

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