Display device and operating method

Abstract

In at least one embodiment, the display device (1) comprises: - a display sheet (2) comprising a plurality of light-emitting pixels (22) and configured for displaying picture content (B) on a front side (20), - a camera system (3) configured to take a calibration image (C) of ambient light (A) arriving at the front side (20), - an ambient light sensor (4) located on a back side (24) of the display sheet (2) opposite the front side (20) and configured to measure a raw luminous power of the ambient light (A) through the display sheet (2), and - a calculation unit (5) configured to: - calculate an angular intensity distribution (H) of the ambient light (A) from the calibration image (C), and - perform an angular correction on the raw luminous power based on the angular intensity distribution (H) to obtain a corrected luminous power.

Description

[0001] Description

[0002] DISPLAY DEVICE AND OPERATING METHOD

[0003] A display device is provided . A method for operating such a display device is also provided .

[0004] Document US 2022 / 0364983 Al refer to an optical property measurement using a sensor behind a display screen .

[0005] Document US 2022 / 0228913 Al refers to improving a detector sensitivity .

[0006] A problem to be solved is to provide a display device that has improved picture quality .

[0007] This obj ect is achieved, inter alia, by a display device and by an operating method as defined in the independent patent claims . Exemplary further developments constitute the sub ect-matter of the dependent claims .

[0008] With the display device described herein, for example , an angular compensation of data from an ambient light sensor, ALS , arranged behind a display sheet can be achieved by using an angular intensity histogram of a camera image .

[0009] According to at least one embodiment , the display device comprises one or a plurality of display sheets . In the following, for simplicity reference is made to j ust one display sheet also there can be more than one display sheet . The display sheet comprises a plurality of light-emitting pixels . For example , the pixels are configured to independently emit red, green, and blue light . Thus , the display sheet is configured for displaying picture content on a front side of the display sheet . The picture content is , for example , an image , a video , or a hologram . The image or the video could either be a two-dimensional or also a three- dimensional representation, like a stereoscopic representation .

[0010] According to at least one embodiment , the display device comprises one or a plurality of camera systems . The at least one camera system is configured to take a calibration image of ambient light arriving at the front side of the display sheet . Hence , by means of the camera system a relative location of an illumination source , like the sun, may be identi fied, the illumination source produces the ambient light shining onto the display sheet . The camera system can be a red-green-blue , RGB, camera or could also be a greyscale camera .

[0011] According to at least one embodiment , the display device comprises one or a plurality of ambient light sensors . Again, in the following reference is made to j ust one ALS also there can be more than one ALS . The ALS is configured to measure a raw luminous power of the ambient light arriving at the display sheet .

[0012] According to at least one embodiment , the ALS is located on a back side of the display sheet . The back side is opposite the front side . Thus , the raw luminous power may be measured through the display sheet .

[0013] According to at least one embodiment , the display device comprises one or a plurality of calculation units . The at least one calculation unit may be implemented in at least one of hardware or software . For example , the calculation unit is software stored in a memory and running on a processor of the display device . The processor may run a plurality of applications or programs so that the processor may not exclusively be assigned to the calculation unit . Otherwise , there can be a distinct processor solely configured for carrying out the actions of the calculation unit .

[0014] According to at least one embodiment , the calculation unit is configured to calculate an angular intensity distribution of the ambient light from the calibration image . For example , each pixel of the camera system is assigned a speci fic angle of incidence , AOI . Thus , pixels having a same radial distance to center pixel , for example , may be assigned to the same AOI . The light intensity of all pixels having the same AOI may be summed up to get an intensity value for said AOI . From all the AOI and the assigned light intensities , the angular intensity distribution is generated, for example , as a histogram . An angular resolution of the angular intensity distribution is , for example , at least 0 . 1 ° or at least 0 . 5 ° and / or is at most 5 ° or is at most 2 ° or is at most 1 ° .

[0015] According to at least one embodiment , the calculation unit is configured to perform an angular correction on the raw luminous power based on the angular intensity distribution to obtain a corrected luminous power . For example , a look-up table is stored in the calculation unit that includes a correspondence factor of intensities in the angular intensity distribution and of intensities measured by the ALS . Hence , each intensity at each angle in the angular intensity distribution can be assigned a correspondence factor, and the correspondence factors can be weighted according to the respective intensity of the respective AOI . Hence , an integral over the angular intensity distribution can be assigned to a scaling factor . This scaling factor can be applied on the raw luminous power to obtain the corrected luminous power, for example . However, there are various possibilities to mathematically implement such a correction with equivalent output .

[0016] In at least one embodiment , the display device comprises :

[0017] - a display sheet comprising a plurality of light-emitting pixels and configured for displaying picture content (B ) on a front side ,

[0018] - a camera system configured to take a calibration image of ambient light arriving at the front side ,

[0019] - an ambient light sensor located on a back side of the display sheet opposite the front side and configured to measure a raw luminous power of the ambient light through the display sheet , and

[0020] - a calculation unit , wherein the calculation unit is configured to :

[0021] - calculate an angular intensity distribution of the ambient light from the calibration image , and

[0022] - perform an angular correction on the raw luminous power based on the angular intensity distribution to obtain a corrected luminous power .

[0023] Ambient light sensors are designed for brightness and correlated color temperature , CCT , detection of ambient light conditions . Compared with the RGB camera system, the sensitivity of ambient light sensors typically include special filters to optimi ze the spectral sensitivity for the standardi zed photopic or the tristimulus function sensitivity of human eye . Also , spectral sensors are used for the reconstruction of the ambient light . The precise spectral information obtained with the ambient light sensor can be used, for example , for supporting display management and automatic white balance , AWB, of camera systems .

[0024] The ALS is placed behind a sel f-emitting display, that is , the display sheet . With this arrangement , the accuracy of the ALS is mainly af fected by the characteristic and setup of the display sheet . First , very low and spectral depending transmission is to be considered . A second aspect to be considered are the field of view, FOV, limiting structures and apertures that af fect the angular depending attenuation which di f fers from a typical Lambertian cosine distribution . These ef fects need to compensate for in order to achieve a reliable determination of illuminance , for example .

[0025] Hence , in the display device described herein, a camera system and an ALS behind a display sheet are combined with each other . The angular brightness histogram of the image taken by the camera system is used to compensate the FOV limiting ef fects of the ALS behind a display . This approach us usable for single channel ALS up to color and spectral sensing behind the sel f-emitting display .

[0026] For example , ef ficient display management and / or white balancing is enabled with such a display device that can perform a high-performance lux measurement from behind a sel f-emitting display .

[0027] According to at least one embodiment , the display sheet is or corresponds to an organic light-emitting diode , OLED, display sheet or a micro light-emitting diode , pLED, display sheet . In an OLED display sheet and a pLED display sheet , the individual pixels are electroluminescent areas made of an organic or inorganic material , respectively .

[0028] Seen in top view, the pixels may have polygonal or round shapes , like square , circular, or regular hexagonal . For example , a diameter or diagonal length of the pixels is less than or equal to 70 pm or less than or equal to 50 pm or less than or equal to 30 pm . This may apply both for OLED display sheets and pLED display sheets .

[0029] According to at least one embodiment , the corrected luminous power and the raw luminous power refer to at least one of illuminance in lux, luminous flux in Im, or irradiance in W / m^ . The luminous power may especially refer to the visible spectral range or part of it . The visible spectral range refers , for example , to wavelengths of at least 420 nm and of at most 750 nm . For example , the luminous power is measured at a wavelength of 555 nm, for example , plus / minus 10 nm .

[0030] According to at least one embodiment , the camera system is located next to the display sheet . For example , seen in top view onto the display sheet the latter and the camera system may not overlap . It is possible that the display sheet and the camera system are placed in a same plane and / or that the camera system terminates flush with the front side . The display sheet and the camera system could be covered by a display cover of the display device , like a cover glass .

[0031] According to at least one embodiment , the camera system is located on the back side of the display sheet . Hence , the camera system can completely or partially be covered by the display sheet . There may be no direct line of sight to the camera system not running through the display sheet . Thus , the camera system can be configured to take the calibration image through the display sheet .

[0032] According to at least one embodiment , the camera system and the display sheet have parallel optical axes . For example , the optical axes are axes of symmetry of the camera' s FOV and a cone of emission of the display sheet , respectively . Analogously, the optical axis of the ALS can be in parallel with the optical axis of the camera system and / or can be in parallel or congruent with the optical axis of the display sheet .

[0033] According to at least one embodiment , the display sheet has a transmittance for visible light of at least 0 . 1 % or of at least 0 . 4 % or at least 1 . 0% . Alternatively or additionally, said transmittance is at most 5% or is at most 3% or is at most 2 % . Said transmittance may be averaged across the whole display sheet . Thus , there may be places of the display sheet that have virtually no transmittance and there may be places have a transmittance of close to 100% , like at least 80% . Hence , the above-stated transmittance values may be average values .

[0034] According to at least one embodiment , the display sheet comprises one or a plurality of light-blocking layers . For example , one light-blocking layer is located at the front side . Alternatively or additionally, a further light-blocking layer may be located at the back side . The at least one light-blocking layer can be of a material or of a layer sequence being opaque for visible light . It is possible that the at least one light-blocking layer is located at a base layer of the display sheet . The base layer may carry the pixels and may include an electric wiring, like metal conductor tracks , and could include electrical switches , like transistors .

[0035] According to at least one embodiment , the at least one lightblocking layer comprises a plurality of apertures . In the apertures , there may be no opaque material or layer sequence of the respective light-blocking layer . Hence , the apertures can be holes in the respective light-blocking layer . The apertures may be of round or polygonal shape , analogous to the pixels .

[0036] I f there is no light-blocking layer, the relatively low transmittance of the display sheet may result from the pixels themselves and / or from the electric wiring and / or the electric switches in the base layer which may be opaque and which need a relatively large area proportion of the display sheet , seen in top view .

[0037] According to at least one embodiment , a diameter or diagonal length of the apertures is at least 2 pm or is at least 6 pm . Alternatively or additionally, said diameter or diagonal length is at most 50 pm or is at most 20 pm or is at most 15 pm . An area proportion of the apertures on the overall light-blocking layer and / or base layer may be , for example , at least 0 . 1 % or at least 0 . 4 % or least 1 . 0% and / or at most 5% or at most 3% or at most 2 % .

[0038] According to at least one embodiment , a plurality of the apertures is located atop a light-entrance face of the ambient light sensor . The light-entrance face may be an area of the ALS configured to receive the light to be detected by the ALS . For example , the light-entrance face has an edge length of at least 70 pm or of at least 100 pm and / or of at most 0.3 mm or of at most 200 pm. For example, a grid dimension of the pixels is at least 20 pm or at least 30 pm and at most 0.2 mm or at most 100 pm. Thus, a number of the apertures located atop the light-entrance face is, for example, at least four or at least nine and / or is at most 300 or is at most 100 or is at most 30. Thus, the ALS may have a relatively high positioning tolerance relative to the display sheet as no exact alignment relative to the pixels may be required .

[0039] According to at least one embodiment, the ambient light sensor is optically directly placed at the back side. Thus, between the ALS and the back side there may not be any optical components intentionally changing an illumination pattern. Such optical components may be lenses or diffusors. One or a plurality of plane-parallel layers of an optical homogeneous component do not lead to a change of the illumination pattern but, in transmission, lead only to a slight parallel shift of radiation.

[0040] According to at least one embodiment, the display device further comprises an optical diffusor. The optical diffusor is located between the back side and the ambient light sensor, or the optical diffusor is part of the ALS. By means of the optical diffusor, an illumination onto the lightentrance face can be made more homogeneous, both concerning AOI and intensity.

[0041] According to at least one embodiment, a distance between the back side and the ambient light sensor, in particular the light-entrance face, is at most 0.6 mm or is at most 0.4 mm or is at most 0.2 mm. It is possible that the light-entrance face is directly at the back side so that the light-entrance face and the back side may touch. For example, the lightentrance face and the back side are oriented in parallel with each other.

[0042] According to at least one embodiment, the ambient light sensor is a single-channel sensor. For example, the ALS is a so-called Y-sensor. A Y-sensor is configured to measure the y-coordinate in the CIE xyz-chromaticity diagram. That is, the ALS may be sensitive in the green spectral range, especially around 555 nm. A spectral sensitivity of the ALS may accordingly correspond to the CIE's color matching function for green light.

[0043] For example, the ALS measurement may fulfil the spectral definition of the 1931 CIE photopic luminosity function for the Y channel sensitivity or spectral reconstruction, that typically differs from spectral characteristic of the camera's color channels. Hence, an integral of the camera green channel histogram cannot be used directly as it may not fulfil the spectral definition of the 1931 CIE photopic luminosity function for the Y channel sensitivity or spectral reconstruction .

[0044] According to at least one embodiment, the ambient light sensor is a three-channel sensor. For example, the ALS has one channel for red light, one channel for green light and one channel for blue light. By way of example, the ALS is a XYZ-sensor measuring the blue, green and red coordinates in the CIE xyz-chromaticity diagram. The channels may thus have spectral sensitivities corresponding to the CIE's color matching functions for blue, green and red light, respectively. Instead of one ALS having three channels it is equivalently possible to have three di f ferent ambient light sensors for blue , green and red light , respectively .

[0045] For example , the three color channels of the ALS may ful fil the spectral definition of the 1931 CIE photopic luminosity function for the X, Y and Z channel sensitivity or spectral reconstruction . As stated above , the camera system' s color channels may not ful fil said spectral definition .

[0046] According to at least one embodiment , the ambient light sensor is a multi-channel sensor . For example , the ALS has at least five or at least eight or at least ten color channels . Alternatively or additionally, the ALS may have at most 25 or at most 16 or at most twelve color channels . Each color channel may be sensitive in a sub-range of the visible spectral range . Instead of one ALS having all the color channels , it is equivalently possible to have a plurality of di f ferent ambient light sensors for one or for groups of the color channels .

[0047] According to at least one embodiment , the ambient light sensor is further configured to measure a raw spectrum of the ambient light . That is , in addition to measure the raw luminous power, the raw spectrum may be obtained . This can be done either by the same ALS , for example , in case of a multichannel ALS , or there is at least one ALS for measuring the raw luminous power and there is at least one ALS for measuring the raw spectrum .

[0048] According to at least one embodiment , the calculation unit is further configured to perform a further angular correction on the raw spectrum based on the angular intensity distribution to obtain a corrected light spectrum . For example , the calculation unit determines an AOI of the external light source by means of the histogram and corrects the color accordingly . Especially for interference-based color filters , also referred to as Bragg filter, the transmission depends on the AOI . Hence , by considering the AOI the light spectrum can be obtained more precisely .

[0049] According to at least one embodiment , the display device comprises one or a plurality of further sensors . Such at least one further sensor may be sensitive in the nearinfrared spectral range , for example , and may be used for distance measurements or face recognition or the like . The near-infrared spectral range may refer to wavelengths of more than 750 nm and of at most 1 . 5 pm or of at most 1 . 1 pm, for example .

[0050] According to at least one embodiment , an ef ficiency of the ambient light sensor has a linear behavior against the AOI of the ambient light sensor . This results , for example , from the base layer provided with the apertures , especially in case of two congruent round apertures in the light-blocking layers . However, there may be some smoothening at the edges of the angular range so that the linear behavior may apply only for up to 75% of the maximum AOI , for example .

[0051] According to at least one embodiment , the display device is a terminal device , like a smart phone or a tablet computer or a laptop . The display device can also be a display installed in a building or a vehicle . For example , the display device is a display in a car, ship or airplane , or the display device is a display in a hotel , museum or venue . Moreover, the display device can be used in outdoor locations with at times predominantly natural ambient light , like amusement parks , traf fic j unctions or sports locations .

[0052] A method for operating the display device is additionally provided . By means of the method, a display device is operated as indicated in connection with at least one of the above-stated embodiments . Features of the display device are therefore also disclosed for the method and vice versa .

[0053] In at least one embodiment , the method is for operating a display device and comprises the following steps , for example , in the stated order :

[0054] - taking, by the camera system, the calibration image of the ambient light arriving at the front side ,

[0055] - measuring, by the ambient light sensor, the raw luminous power of the ambient light through the display sheet ,

[0056] - calculating, by the calculation unit , the angular intensity distribution f the ambient light from the calibration image ,

[0057] - performing, by the calculation unit , the angular correction on the raw luminous power based on the angular intensity distribution to obtain the corrected luminous power,

[0058] - optionally adapting, by the calculation unit , raw picture content to the corrected luminous power to obtain the picture content , and

[0059] - optionally showing, by the display sheet , the picture content .

[0060] A computer program and a computer-readable storage medium comprising instructions which, when the program is executed by a computer, cause the computer to carry out the operating method, are further disclosed . A display device and a method described herein are explained in greater detail below by way of exemplary embodiments with reference to the drawings . Elements which are the same in the individual figures are indicated with the same reference numerals . The relationships between the elements are not shown to scale , however, but rather individual elements may be shown exaggeratedly large to assist in understanding .

[0061] In the figures :

[0062] Figure 1 is a schematic sectional view of an exemplary embodiment of a display device described herein,

[0063] Figure 2 is a schematic top view of an exemplary embodiment of a display device described herein,

[0064] Figure 3 is a schematic sectional view of an exemplary embodiment of a display device described herein,

[0065] Figure 4 is a schematic top view of a display sheet for display devices described herein,

[0066] Figure 5 is a schematic partial sectional view of the display sheet of Figure 4 ,

[0067] Figure 6 is a schematic representation of ef ficiencies in dependency of an angle of incidence for camera systems and ambient light sensors for display devices described herein,

[0068] Figure 7 is a schematic top view of a camera system for display devices described herein, Figures 8 to 10 are schematic representations of optical properties of camera systems for display devices described herein,

[0069] Figure 11 is a schematic block diagram of an exemplary embodiment of an operating method for display devices described herein,

[0070] Figures 12 and 13 are schematic sectional views of exemplary embodiments of display devices described herein,

[0071] Figure 14 is a schematic representation for correcting light spectra of ambient light sensors for display devices described herein,

[0072] Figures 15 and 16 are schematic representations of optical properties of camera systems for display devices described herein, and

[0073] Figures 17 and 18 are schematic representations of powers in dependency of an angle of incidence for camera systems and ambient light sensors for display devices described herein .

[0074] Figure 1 and 2 illustrates an exemplary embodiment of a display device 1 . The display device 1 comprises a display sheet 2 . The display sheet 2 has a plurality of lightemitting pixels 22 . The pixels 22 are to display picture content B on a front side 20 . The picture content B could be an image or a video , for example . There may be pixels 22 for red, green and blue light so that the display device 1 can be an RGB device . The display sheet 2 may be of plane fashion or also of curved fashion . As shown in Figure 1 , the display sheet 2 is mechanically rigid, however, mechanically flexible , that is , bendable , display sheets 2 can also be used .

[0075] Further, the display device 1 includes a camera system 3 . The camera system 3 is to take images . The camera system 3 ma take , for example , a calibration image C of ambient light A arriving at the front side 20 . As calibration image C, in principle any image taken by the camera system 3 can be suitable . However, it is possible that the calibration image C is taken when the display sheet 2 is turned of f wherein a short of f-period, like less than 50 ms or less than 20 ms , may suf fice . Otherwise , the calibration image C may be recorded when the display sheet 2 is in a normal on-state . An optical axis 02 of the camera system 3 may be in parallel with an optical axis 01 of the display sheet 2 . The camera system 3 can be an RGB camera, for example .

[0076] The display device 1 further has an ambient light sensor 4 , ALS for short , located on a back side 24 of the display sheet 2 . The back side 24 is a main side of the display sheet 2 opposite the front side 20 . The ALS 4 is to measure a raw luminous power of the ambient light A arriving at the display sheet 2 . Thus , the ALS 4 measures the ambient light A through the display sheet 2 .

[0077] An optical axis 03 of the ALS 4 may be in parallel or congruent with the optical axis 01 of the display sheet 2 . The ALS 4 can be a single-channel detector or also a multichannel detector . The ALS 4 may be located directly or closely at the back side 24 . Moreover, the display device 1 includes a calculation unit 5 . The calculation unit 5 is configured to calculate an angular intensity distribution H of the ambient light A from the calibration image C, and to perform an angular correction on the raw luminous power based on the angular intensity distribution H to obtain a corrected luminous power .

[0078] The calculation unit 5 may comprise a processor and a memory . A computer program to carry out the necessary steps can be stored in the memory . The processor can be a processor exclusively used by the calculation unit 5 or the calculation unit 5 uses a processor in equipment the display device is built in . Hence , the calculation unit 5 may be a computer program . The calculation unit 5 may also include control means to control the display sheet 2 , the camera system 3 and / or the ALS 4 .

[0079] In Figure 2 it is shown that the display device 1 is part of the equipment which is , for example , a smart phone 10 . Otherwise , the display device 1 may be built into a car or into a building, not shown . As can be seen from Figure 2 , the camera system 3 may not overlap with the display sheet 2 . The display sheet 2 may partially or completely surround the camera system 3 , seen in top view . The calculation unit 5 may be a software running onto a processor of the smart phone 10 , for example . The camera system 3 may thus be a camera used for video talks or sel fies , for example . Hence , the camera system 3 may not need to be a component exclusively used in connection with the ALS 4 only .

[0080] Otherwise , the same as to Figure 1 may also apply to Figure 2 , and vice versa . In Figure 3 it is illustrated that both the ALS 4 and the camera system 3 are located on the back side 24 of the display sheet 2 . Thus , the calibration image C may be recorded through the display sheet 2 . In other words , some of the pixels 22 of the display sheet 2 can be arranged atop the camera system 3 , for example , atop a camera chip 32 of the camera system 3 , like a CCD chip . In this configuration, the camera system 3 may exclusively be used in connection with the ALS 4 , however, the camera system 3 may also have other functions like face recognition, f itness-to-drive surveillance , or the like .

[0081] Otherwise , the same as to Figures 1 and 2 may also apply to Figure 3 , and vice versa .

[0082] In Figures 4 and 5 the display sheet 2 is illustrated in more detail . On the front side 20 , there are light-emitting regions corresponding to red emitting pixels 22R, blue emitting pixels 22B and green emitting pixels 22G . For example , an image point of the picture B is composed of one red emitting pixel 22R, one blue emitting pixel 22B and two green emitting pixels 22G . The pixels 22G, 22R, 22B may be arranged in a rhombic grid, for example .

[0083] At the front side 20 and optionally also at the back side 24 there are light-blocking layers 25 which are made , for example , of black chromium . The light-blocking layers 25 are opaque for visible light . The light-blocking layers 25 each comprise a plurality of apertures 26 which are holes in the light-blocking layers 25 .

[0084] For example , the light-blocking layers 25 are arranged on two main sides of a base layer 27 of the display sheet 2 . The base layer 27 may mechanically carry the display sheet 2 and may include an electric wiring for the pixels 22R, 22G, 22B, not shown. For example, the base layer 27 includes a transparent base material like a glass or plastics. Thus, visible light can travel through the base layer 27 from the front side 20 to the back side 24 where the apertures 26 are located. A refractive index of the base material may be around 1.5 for green light.

[0085] The light-blocking layers 25 may be applied on the base layer 27 so that the light-blocking layers 25 protrude from the base layer 27. Otherwise, the light-blocking layers 25 and the base layer 27 may terminate flush so that a common plane is formed by the respective light-blocking layer 25 and the base layer 27, contrary to what is shown in Figure 5.

[0086] A cone L corresponds to a maximum angular range from which light can enter the base layer 27 and can thus reach the ALS 4 through the apertures 26. The cone L may be symmetrically round the optical axis 03 of the ALS 4. An angle of incidence AOI is zero at the optical axis 03. For example, at the cone

[0087] L the AOI is around 70° or around 75°.

[0088] A thickness T of the base layer 27 is, for example, at least 4 pm and / or at most 50 pm or at most 20 pm. The thickness T may be around 12 pm. A diameter D or diagonal length of the apertures 26 is, for example, at least 5 pm and / or at most 20 pm. For example, the diameter D is around 10 pm.

[0089] Because the ALS 4 is located at the back side 24, an efficiency Eff of the ALS 4 deviates from a cosine function, see Figure 6. Thus, the efficiency Eff has a nearly linear dependency on the AOI . Contrary to that, the camera system 3 may have an efficiency Eff running above the cosine function, that is, at least at small AOI values the camera system 3 may be more efficient than a Lambertian surface. Because of the non-cosine efficiency function of the ALS 4, a signal of the ALS 4 needs to be adapted to its location behind the display sheet 2. This is explained in more detail in connection with Figures 7 to 10.

[0090] In Figure 7 the taking the calibration image C is shown in more detail wherein the calibration image C can in principle by any image taken by the camera system 3. By a camera lens 31, an external light source 9, like the sun or an artificial light source, is imaged onto a camera chip 32, like a CCD chip. Hence, the calibration image C results. A position of the external light source 9 on the camera chip 32 dependents on the AOI .

[0091] Thus, different camera pixels 33 correspond to different

[0092] AOIs, compare Figure 8. In Figure 8, for an exemplary camera chip 32 the camera pixels 33 are assigned to various AOIs. At a central pixel 34, the AOI is zero.

[0093] In Figure 9 it is illustrated that in the calibration image C each one of the camera pixels 33 has a pixel intensity 35. At the location of the external light source 9 on the camera chip 32, the pixel intensity 35 is at its maximum.

[0094] Thus, taking Figures 8 and 9 together, to each AOI an intensity value can be assigned, and an angular intensity distribution H can be generated, compare Figure 10. For example, the intensities of all camera pixels 33 corresponding to an angle of 30° are added together, and the respective sum is assigned to a value for 30° in the angular intensity distribution H . In the example of Figure 10 , a maximum intensity I is around 37 ° .

[0095] I f the ALS 4 is originally calibrated to a cosine behavior of a Lambertian surface , compare Figure 6 , without correction the raw luminous power measured by the ALS 4 would signi ficantly deviate from a true luminous power . Thus , using the angular intensity distribution H as exemplarily shown in Figure 10 allows for correction of the real dependency, compare Figure 6 , to model the calibrated behavior . That is , for example , the angular intensity distribution H is scaled on the cosine behavior by considering the angular sensitivity behavior of the camera system 3 and the ALS 4 , see the exemplary curves in Figure 8 .

[0096] The corresponding operating method of the display device 1 is schematically illustrated in Figure 11 .

[0097] According to method step Mi l , the calibration image C of the ambient light A is taken by the camera system 3 . The calibration image C may exclusively be taken for correcting the data from the ALS 4 , or the calibration image C is an image taken within another application, like a video call , shortly before or after the respective measurement done by the ALS 4 . In method step M12 , the ALS 4 measures the raw luminous power of the ambient light A through the display sheet 2 . Method steps Mi l and M12 should refer to the same illumination conditions concerning the ambient light . These method steps may be repeated periodically or when triggered, for example , by a user .

[0098] In method step M13 , the angular intensity distribution H of the ambient light A is calculated by the calculation unit 5 from the calibration image C . Then, in method step M14 the angular correction is performed on the raw luminous power based on the angular intensity distribution H to obtain the corrected luminous power, like the illuminance in lux .

[0099] Optionally, in method step M15 , for example , by the calculation unit 5 , raw picture content is adapted to the corrected luminous power to obtain the picture content B, and in optional method step M16 the picture content B is shown by the display sheet 2 . For example , a brightness of the picture content B is adapted so that the picture content B can well be seen on the display sheet 2 given the illuminance at the display sheet 2 due to the ambient light A.

[0100] Thus , the method may be summari zed as follows :

[0101] The digital camera 3 is taking the image C . Each pixel 33 corresponds to a speci fic AOI . A calibrated camera may also include information about distortions and compensated cosine attenuation ef fects . Having the power for each pixel 33 , a histogram H over the AOI describes the angular condition of the real scenery with respect to the ambient light A.

[0102] An OLED display, for instance , has an array of apertures 26 on top and bottom sides 20 , 24 . Distance and diameter of the apertures 26 define the field of view and the angular distribution of the transmittance through the display sheet 2 . The angular distribution covers a range up to 70 ° hal fcone angle , for example , but is not cosine-like . The ALS 4 collects all the light transmitted through the display sheet 2 and is located in a short distance or direct in contact behind the display sheet 2 covering multiple of the apertures 26 . By the knowledge about the angular distribution of a bright light source in the scenery and the angular transmittance of the display apertures 26, the ALS output can be scaled to real photopic brightness according to the cosine distribution or the fully compensated one.

[0103] Otherwise, the same as to Figures 1 to 10 may also apply to

[0104] Figure 11, and vice versa.

[0105] According to Figure 12, as an option there is an optical diffusor 6 between the back side 24 and the ALS 4. The optical diffusor 6 is, for example, a sheet with at least one roughened surface or a volume diffusor containing lightscattering structures. By having the optical diffusor 6, the light-entrance face 40 can be illuminated more homogeneously.

[0106] Optionally, as also shown in Figure 12, the ALS4 may be adhered to the back side 24 using an adhesive 7, like a glue. Such an adhesive can also be present between the optical diffusor 6 and the ALS 4, not shown, or the optical diffusor 6 can be part of the ALS 4.

[0107] Such an optical diffusor 6 and / or such at least one adhesive may also be present in all other examples. A distance between the back side 24 and the ALS 4 is, for example, at most 0.6 mm.

[0108] Further, in Figure 12 it is illustrated that the ALS 4 includes a color filter 42 placed on a sensor chip 41. For example, the sensor chip 41 is based on silicon. The color filter 42 may be an interference filter. This may also apply to all other examples of the display device 1. In Figure 13 it is shown that the ALS 4 is directly applied at the back side 24 . An adhesive 7 for doing so may be placed next to the light-entrance face 40 or the ALS 4 may be pressed onto the back side 24 by another component , not shown .

[0109] Otherwise , the same as to Figures 1 to 11 may also apply to Figure 12 and 13 , and vice versa .

[0110] The ALS 4 may not only be used to determine the luminous power but also to determine a spectrum of the ambient light in the visible spectral range , especially i f the ALS 4 is a multi-channel sensor wherein the individual channels are sensitive in di f ferent sub-ranges of the visible spectral range .

[0111] As the spectral sub-ranges may be defined by the color filters 42 and as the color filters 42 may have an angularly dependent transmittance , as in the case of interference filters , a raw spectrum Q of the ambient light A as measured by the ALS 4 may deviate from a real light spectrum because of an AOI di f ferent from 0 ° . Hence , the angular intensity distribution H may also be used to correct this ef fect to obtain a corrected light spectrum S , see Figure 14 .

[0112] Accordingly, the method as shown in Figure 11 may optionally include a method step M21 in which the raw spectrum Q of the ambient light A is measured . Then, in method step M22 a further angular correction on the raw spectrum Q can be performed based on the angular intensity distribution H to obtain the corrected light spectrum S . This could be done , for example , by the calculation unit 5 as well . In Figure 15 , another example of a calibration image C is shown which comprises two areas of high intensity corresponding to two external light sources , for example . The corresponding angular intensity distribution H is illustrated in Figure 16 . Even with more than one external light source , by the method as explained in connection with Figures 8 to 11 a corrected luminous power can be calculated .

[0113] In connection with Figures 17 and 18 , the correction of the luminous power is referred to in more detail . For example , a recalculation angular power can be obtained from a crosssection Pl [W / sr ] into an ef fective angle P2 [W] :

[0114] - The cross-section, as shown in Figure 6 , describes power values on the x and y axis .

[0115] - For circular symmetrical conditions , all four directions , that is , north, west , south, east , are similar .

[0116] - For a color filter with an angular dependency, like an interference filter, only the ef fective AOI is relevant :

[0117] 180° / OC* 7T\ asin (sin — — - * E sr) V180 ° / “7wherein the AOI is referred to as a, Pl is referred to as E_sr and P2 is referred to as E . That is , the curves of Figure 17 may be based on Figure 6 , and the curves of Figure 18 can be obtained from Figure 17 .

[0118] Calculating the angular intensity distribution H of Figure 10 and performing the angular correction may be done according to the following scheme , for example :

[0119] Based on the following definitions of variables : oc= 0: n° => angular vector

[0120] CameraDist(oE) => angular distribution of camera incl. by lens distortion

[0121] SensorDist(oG) => angular distribution of sensor

[0122] Histogramfc ), = sum power of similar effective AOI

[0123] => effctive angular distribution form camera

[0124] The following calculation may be performed :

[0125] SensorSignal => output signal of the sensor

[0126] E_Ref[lx] => reference x measurement with calibrated device

[0127] => scaling factor from white balancing at perpendicular irradiance

[0128] Compensation to the Lambertian distribution may be done as follows :

[0129] LambertE[lx] =

[0130] Compensation to the camera system' s distribution may be done as follows :

[0131] The components shown in the figures follow, unless indicated otherwise , exemplarily in the speci fied sequence directly one on top of the other . Components which are not in contact in the figures are exemplarily spaced apart from one another . I f lines are drawn parallel to one another, the corresponding surfaces may be oriented in parallel with one another .

[0132] Likewise , unless indicated otherwise , the positions of the drawn components relative to one another are correctly reproduced in the figures .

[0133] The invention described here is not restricted by the description on the basis of the exemplary embodiments .

[0134] Rather, the invention encompasses any new feature and also any combination of features , which includes in particular any combination of features in the patent claims , even i f this feature or this combination itsel f is not explicitly speci fied in the patent claims or exemplary embodiments .

[0135] This patent application claims the priority of German patent application 10 2024 108 777 . 3 , the disclosure content of which is hereby incorporated by reference .

[0136] References

[0137] 1 display device

[0138] 2 display sheet

[0139] 20 front side

[0140] 22 light-emitting pixel

[0141] 24 back side

[0142] 25 light-blocking layer

[0143] 26 aperture

[0144] 27 base layer

[0145] 3 camera system

[0146] 31 camera lens

[0147] 32 camera chip

[0148] 33 camera pixel

[0149] 34 central camera pixel at the optical axis

[0150] 35 pixel intensity

[0151] 4 ambient light sensor, ALS

[0152] 40 light-entrance face

[0153] 41 sensor chip

[0154] 42 color filter

[0155] 5 calculation unit

[0156] 6 optical di f fusor

[0157] 7 adhesive

[0158] 9 external light source

[0159] 10 smart phone

[0160] A ambient light

[0161] AOI angle of incidence

[0162] B picture

[0163] C calibration image

[0164] D diameter of the apertures

[0165] Ef f ef ficiency

[0166] H angular intensity distribution

[0167] I signal intensity L cone of maximum angular range for accepting light

[0168] M method step

[0169] 0 optical axis

[0170] Pl power distribution in W7 sr P2 power distribution in W

[0171] Q raw spectrum of the ambient light

[0172] S corrected light spectrum

[0173] T thickness of the base layer

[0174] W wavelength

Claims

Claims1. A display device (1) comprising:- a display sheet (2) comprising a plurality of lightemitting pixels (22) and configured for displaying picture content (B) on a front side (20) ,- a camera system (3) configured to take a calibration image (C) of ambient light (A) arriving at the front side (20) ,- an ambient light sensor (4) located on a back side (24) of the display sheet (2) opposite the front side (20) and configured to measure a raw luminous power of the ambient light (A) through the display sheet (2) , and- a calculation unit (5) , wherein the calculation unit (5) is configured to:- calculate an angular intensity distribution (H) of the ambient light (A) from the calibration image (C) , and- perform an angular correction on the raw luminous power based on the angular intensity distribution (H) to obtain a corrected luminous power.

2. The display device (1) according to the preceding claim, wherein the display sheet (2) is an organic light-emitting diode, OLED, display sheet or a micro light-emitting diode, pLED, display sheet.

3. The display device (1) according to any one of the preceding claims, wherein the corrected luminous power refers to at least one of illuminance in lux, luminous flux in Im, or irradiance in W / m^ .

4. The display device (1) according to any one of the preceding claims,wherein the camera system (3) is located next to the display sheet (2) , and the camera system (3) and the display sheet (2) have parallel optical axes (01, 02) .

5. The display device (1) according to claim 1, 2 or 3, wherein the camera system (3) is located on the back side(24) of the display sheet (2) so that the camera system (3) is configured to take the calibration image (0) through the display sheet (2) .

6. The display device (1) according to any one of the preceding claims, wherein the display sheet (2) has a transmittance for visible light of at least 1% and of at most 3%.

7. The display device (1) according to the preceding claim, wherein the display sheet (2) comprises a light-blocking layer (25) at the front side (20) , the light-blocking layer(25) has a plurality of apertures (26) , wherein a diameter (D) of the apertures (26) is between 2 pm and 50 pm inclusive.

8. The display device (1) according to the preceding claim, wherein a plurality of the apertures (26) is located atop a light-entrance face (40) of the ambient light sensor (4) .

9. The display device (1) according to any one of the preceding claims, wherein the ambient light sensor (4) is optically directly placed at the back side (24) .

10. The display device (1) according to any one of claims 1 to 8 ,further comprising an optical diffusor (6) , wherein the optical diffusor (6) is located between the back side (24) and the ambient light sensor (4) , wherein a distance between the back side (24) and the ambient light sensor (4) is at most 0.6 mm.

11. The display device (1) according to any one of the preceding claims, wherein the ambient light sensor (4) is a single-channel sensor .

12. The display device (1) according to any one of claims 1 to 10, wherein the ambient light sensor (4) is a three-channel sensor having one channel for red light, one channel for green light and one channel for blue light.

13. The display device (1) according to any one of claims 1 to 10, wherein the ambient light sensor (4) is a multi-channel sensor having at least five and at most 25 different color channels , wherein the ambient light sensor (4) is further configured to measure a raw spectrum (Q) of the ambient light (A) .

14. The display device (1) according to the preceding claim, wherein the calculation unit (5) is further configured to:- perform a further angular correction on the raw spectrum (Q) based on the angular intensity distribution (H) to obtain a corrected light spectrum (S) .

15. The display device (1) according to any one of the preceding claims,wherein an efficiency (E) the ambient light sensor (4) has a linear behavior against an angle of incidence (AOI) of the ambient light sensor (4) .

16. The display device (1) according to any one of the preceding claims, which is configured to be built into a smart phone (10) .

17. The display device (1) according to any one of the preceding claims, wherein the calculation unit (5) is configured so that the calculating the angular intensity distribution (H) comprises: each pixel of the camera system is assigned a specific angle of incidence, AOI; pixels having a same radial distance to a center pixel are assigned to the same AOI; the light intensity of all pixels having the same AOI is summed up to get an intensity value for said AOI; from all the AOI and the assigned light intensities, the angular intensity distribution is generated; each intensity at each angle in the angular intensity distribution is assigned a correspondence factor, and the correspondence factors are weighted according to a respective intensity of the respective AOI; and an integral over the angular intensity distribution is assigned to a scaling factor, the scaling factor is applied on the raw luminous power to obtain the corrected luminous power .

18. A method for operating a display device (10) according to any one of the preceding claims comprising the following steps :- taking, by the camera system (3) , the calibration image (C)of the ambient light (A) arriving at the front side (20) ,- measuring, by the ambient light sensor (4) , the raw luminous power of the ambient light (A) through the display sheet ( 2 ) ,- calculating, by the calculation unit (5) , the angular intensity distribution (H) of the ambient light (A) from the calibration image (C) ,- performing, by the calculation unit (5) , the angular correction on the raw luminous power based on the angular intensity distribution (H) to obtain the corrected luminous power,- adapting, by the calculation unit (5) , raw picture content to the corrected luminous power to obtain the picture content (B) , and- showing, by the display sheet (2) , the picture content (B) .

19. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of the preceding claim.

20. A computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to carry out the method of claim 18.

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