Point spread function estimation system and method

Abstract

A point spread function estimation system, including: an electronic visual display configured to present a dot pattern; a camera arranged to detect a part of the light originating from the dot pattern presented on the electronic visual display, wherein the camera is configured to capture an image for estimating a point spread function of the camera; and a colored glass filter arranged and configured to filter the part of the light originating from the dot pattern presented on the electronic visual display such that a predetermined wavelength band is transmitted through the colored glass filter and incident on the camera.

Description

[0001] POINT SPREAD FUNCTION ESTIMATION SYSTEM AND METHOD

[0002] TECHNICAL FIELD

[0003] The present disclosure generally pertains to a point spread function estimation system and a method for estimating a point spread function.

[0004] TECHNICAL BACKGROUND

[0005] Generally, the point spread function describes the response of a camera or an optical imaging system such as lens to a point light source. In other words, it is the impulse response of an optical imaging system. The PSF can be used for determining the effective spatial resolution of a lens or a camera.

[0006] Known methods include the slanted edge method that makes use of custom-made charts usually having horizontal and vertical edge objects to measure the modulation transfer function (“MTF”).

[0007] However, the slanted-edge method typically provides only ID MTF data for horizontal, vertical and diagonal directions lacking capability to estimate 2D PSFs of the camera.

[0008] A display -based PSF estimation system is known from F. Navas-Moya et al., “Measurement of the optical transfer function using a white-dot pattern presented on a liquid-crystal display”, J. Europ. Opt. Soc. Rap. Public. 8, 13029 (2013).

[0009] However, there a liquid-crystal display (“LCD”) is used which may have an emission spectrum that may not cover the whole visible wavelength range, e.g., from about 400 up to about 700 nm.

[0010] Moreover, the used liquid-crystal tunable filter (“LCTF”) used there has an angle of incidence dependence, which may, in some cases, influence the estimation of the point spread function.

[0011] Additionally, three images are captured (white, dot and black) there for the estimating the point spread function.

[0012] Although there exist techniques for estimating a point spread function of a camera, it is generally desirable to improve the existing techniques.

[0013] SUMMARY

[0014] According to a first aspect, the disclosure provides a point spread function estimation system, comprising: an electronic visual display configured to present a dot pattern; a camera arranged to detect a part of the light originating from the dot pattern presented on the electronic visual display, wherein the camera is configured to capture an image for estimating a point spread function of the camera; and a colored glass filter arranged and configured to filter the part of the light originating from the dot pattern presented on the electronic visual display such that a predetermined wavelength band is transmitted through the colored glass filter and incident on the camera.

[0015] According to a second aspect, the disclosure provides a method for estimating a point spread function, comprising: presenting a dot pattern on an electronic visual display; capturing an image with a camera arranged to detect a part of the light originating from the dot pattern presented on the electronic visual display; and filtering the part of the light originating from the dot pattern presented on the electronic visual display by a colored glass filter such that a predetermined wavelength band is transmitted through the colored glass filter and incident on the camera.

[0016] Further aspects are set forth in the dependent claims, the drawings and the following description.

[0017] BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Embodiments are explained by way of example with respect to the accompanying drawings, in which:

[0019] Fig. 1 A schematically illustrates in a block diagram an embodiment of a point spread function estimation system;

[0020] Fig. IB schematically illustrates an embodiment of a dot pattern presented on an electronic visual display;

[0021] Fig. 2A schematically illustrates in a block diagram an embodiment of a point spread function estimation system;

[0022] Fig. 2B schematically illustrates an embodiment of a dot pattern presented on an electronic visual display;

[0023] Fig. 3 schematically illustrates in graphs embodiments of spectral transmittance profiles of colored glass filters;

[0024] Fig. 4 schematically illustrates in a flow diagram an embodiment of a method for estimating a point spread function; and Fig. 5 schematically illustrates in a flow diagram an embodiment of a method for estimating a point spread function.

[0025] DETAILED DESCRIPTION OF EMBODIMENTS

[0026] Before a detailed description of the embodiments under reference of Fig. 1 A is given, general explanations are made.

[0027] As mentioned in the outset, a display-based PSF estimation system is known from F. Navas- Moya et al., “Measurement of the optical transfer function using a white-dot pattern presented on a liquid-crystal display”, J. Europ. Opt. Soc. Rap. Public. 8, 13029 (2013).

[0028] However, there a liquid-crystal display (“LCD”) is used which may have an emission spectrum that may not cover the whole visible wavelength range, e.g., from about 400 up to about 700 nm.

[0029] Moreover, the used liquid-crystal tunable filter (“LCTF”) used there has an angle of incidence dependence, which may, in some cases, influence the estimation of the point spread function.

[0030] Additionally, three images are captured (white, dot and black) there for the estimating the point spread function.

[0031] An improved electronic visual display -based point spread function estimation system is proposed herein.

[0032] Hence, some embodiments pertain to a point spread function estimation system, wherein the point spread function estimation system includes: an electronic visual display configured to present a dot pattern; a camera arranged to detect a part of the light originating from dot pattern presented on the electronic visual display, wherein the camera is configured to capture an image for estimating a point spread function of the camera; and a colored glass filter arranged and configured to filter the part of the light originating from dot pattern presented on the electronic visual display such that a predetermined wavelength band is transmitted through the colored glass filter and incident on the camera.

[0033] The electronic visual display may be an active or a passive electronic visual display. In some embodiments, in which the electronic visual display is a passive electronic visual display, the point spread function estimation system further includes a light source arranged to illuminate the passive electronic visual display. The electronic visual display may be an organic light emitting diode display, an electronic paper display, a liquid crystal display, a quantum dot display, a plasma display, an electroluminescent display, etc.

[0034] Thus, in some embodiments, the electronic visual display is an organic light emitting diode display.

[0035] Typically, organic light emitting diode displays have sufficient spectral power over the whole visible light range (e.g., from about 400 nm up to about 700 nm).

[0036] Each dot in the dot pattern corresponds to a light emitting (for active electronic visual displays) or reflecting (for passive electronic visual displays that are, e.g., illuminated by a light source) pixel.

[0037] It has been recognized that, on the one hand, the size of each of a plurality of separated single dots in the presented dot pattern may be too small for estimating the point spread function, since the light emitted or reflected by each separated single dot may be imaged on a single image pixel in the camera such that the captured image may not appropriately represent the point spread function.

[0038] Thus, in some embodiments, the dot pattern includes a NxN block of dots, wherein N is an Integer and larger than one.

[0039] On the other hand, to behave as a point source, a size of a NxN block of dots may be smaller than a single image pixel of the camera.

[0040] Moreover, depending on the distance between the camera and the electronic visual display and the field-of-view of the camera, the resulting representation in the captured image may be smaller or larger.

[0041] Thus, in some embodiments, N is based on the field-of-view of the camera and the distance between the camera and the electronic visual display.

[0042] It has further been recognized that the point spread function should be estimated for different heights of the dot pattern with respect to the camera for estimating the point spread function also for point light sources which are not on the optical axis of the camera.

[0043] In particular, if the electronic visual display is too small to cover the whole field-of view ("FOV”) of the camera, the electronic visual display may be moved around to cover the whole FOV. Otherwise, in some embodiments, there may be no need to move the electronic visual display. Thus, in some embodiments, the point spread function estimation system further includes a holder configured to hold and move the electronic visual display in at least one direction with respect to the camera for presenting the dot pattern in a plurality of different positions.

[0044] In some embodiments, the optical axis of the camera is horizontally arranged and the at least one direction is the vertical direction.

[0045] In some embodiments, the camera is configured to capture, for each position of the plurality of different positions, an image for estimating the point spread function for each position.

[0046] In some embodiments, the electronic visual display is an electronic paper display, and the point spread function estimation system further includes a broadband light source arranged to illuminate the electronic paper display, wherein the broadband light source has a light emission spectrum including at least a part of the visible light spectrum and a part of the near-infrared light spectrum.

[0047] The broadband light source may be, for example, a Quartz Tungsten Halogen (“QTH”) lamp or a Xenon lamp.

[0048] Thereby, also the near-infrared (“NIR”) range is covered, wherein the NIR range covers, e.g., wavelength from about 700 nm up to about 1000 nm.

[0049] Thus, in some embodiments, the predetermined wavelength band is a near-infrared wavelength band.

[0050] In some embodiments, the point spread function estimation system further includes an information processing device configured to estimate the point spread function of the camera based on the captured image.

[0051] The point spread function may be estimated by detecting image pixels in the captured image having an image pixel value (e.g., grey value of color value) above a predetermined threshold such that the point spread function is extracted from the captured image based on the predetermined threshold. A normalization step may be performed afterwards.

[0052] This may be performed solely based on a single captured image, however, a dark image may improve the accuracy in some embodiments.

[0053] In some embodiments, the information processing device is further configured to estimate the point spread function further based on a dark image captured by the camera.

[0054] The dark image may be subtracted from the captured image before applying the predetermined threshold for extracting the point spread function. Generally, the use of a colored glass filter eliminates the angle of incidence dependency of the point spread function which may be present in other optical filters.

[0055] Some embodiments pertain to a (corresponding) method for estimating a point spread function, wherein the method includes: presenting a dot pattern on an electronic visual display; capturing an image with a camera arranged to detect a part of the light originating from the dot pattern presented on the electronic visual display; and filtering the part of the light originating from the dot pattern presented on the electronic visual display by a colored glass filter such that a predetermined wavelength band is transmitted through the colored glass filter and incident on the camera.

[0056] In some embodiments, the method includes presenting the dot pattern on an organic light emitting diode display.

[0057] In some embodiments, the dot pattern includes a NxN block of dots, wherein N is an Integer and larger than one.

[0058] In some embodiments, N is based on the field-of-view of the camera and the distance between the camera and the electronic visual display.

[0059] In some embodiments, the method includes moving the electronic visual display in at least one direction with respect to the camera for presenting the dot pattern in a plurality of different positions.

[0060] As mentioned above, in particular, if the electronic visual display is too small to cover the whole FOV of the camera, the electronic visual display may be moved around to cover the whole FOV. Otherwise, in some embodiments, there may be no need to move the electronic visual display.

[0061] In some embodiments, the method includes capturing, for each position of the plurality of different positions, an image for estimating the point spread function for each position.

[0062] In some embodiments, the method includes: presenting the dot pattern on an electronic paper display; and illuminating the electronic paper display with a broadband light source, wherein the broadband light source has a light emission spectrum including at least a part of the visible light spectrum and a part of the near-infrared light spectrum.

[0063] In some embodiments, the predetermined wavelength band is a near-infrared wavelength band. In some embodiments, the method includes estimating the point spread function of the camera based on the captured image.

[0064] In some embodiments, the method includes estimating the point spread function further based on a dark image captured by the camera.

[0065] Returning to Fig. 1 A, which schematically illustrates in a block diagram an embodiment of a point spread function estimation system 1, which is discussed in the following.

[0066] The point spread function estimation system 1 includes an electronic visual display 2, a camera 3, a colored glass filter 4 (“CGF”) and an information processing device 6.

[0067] The electronic visual display 2 is an organic light emitting diode (“OLED”) display (including, e.g., an AMOLED (“Active-Matrix OLED”) display as an embodiment).

[0068] The OLED display 2 is arranged such that a field-of-illumination (“FOI”) overlaps with a field- of-view (“FOV”) of the camera 3.

[0069] The OLED display 2 presents a dot pattern 9, which is schematically illustrated in Fig. IB.

[0070] The OLED display 2 has dark pixels 8 and light emitting pixels which are arranged as a 2x2 block.

[0071] A part 5 of the light originating from the dot pattern 9 presented on the OLED display 2 transmits through the CGF 4 and is detected by the camera 3 which captures an image for estimating the point spread function of the camera 3.

[0072] The CGF 4 may have, for instance, a spectral transmittance profile as schematically illustrated in graphs in Fig. 3.

[0073] The CGF 4 may have a red CGF profile 30, a green CGF profile 31 or a blue CGF profile 32 such that a predetermined wavelength band is transmitted through the CGF 4 and incident on the camera 3.

[0074] For example, when the CGF 4 has the red CGF profile 30, wavelengths of about 600 nm up to about 700 nm are transmitted such that the point spread function is estimated in the red spectral region.

[0075] For instance, when the CGF 4 has the green CGF profile 31, wavelengths of about 500 nm up to about 600 nm are transmitted such that the point spread function is estimated in the green spectral region. When the CGF 4 has, e.g., the blue CGF profile 32, wavelengths of about 400 nm up to about 500 nm are transmitted such that the point spread function is estimated in the blue spectral region.

[0076] Moreover, a dark image is captured by the camera 3 where the dot pattern 9 is not presented on the OLED display 2.

[0077] The captured image and the captured dark image are transmitted from the camera 3 to the information processing device 6 which estimates the point spread function based on the obtained images.

[0078] Additionally, the OLED display 2 is mounted on a holder 7 which can move the OLED display 2 up and down such that an image - and optionally also a dark image - can be captured at a plurality of different heights.

[0079] Generally, the estimation of the point spread function in the near-infrared range may be useful, for example, for optimizing depth sensor performance.

[0080] Fig. 2A schematically illustrates in a block diagram an embodiment of a point spread function estimation system 20, which is discussed in the following.

[0081] The point spread function estimation system 20 includes an electronic visual display 21, a camera 23 (here, e.g., a depth sensor), a CGF 24, the information processing device 6 and a broadband light source 22.

[0082] The electronic visual display 21 is an electronic paper display (“e-paper” in the following), wherein the broadband light source 22 has a FOI 25 such that the e-paper 21 is illuminated.

[0083] The e-paper 21 presents the dot pattern 9 indirectly, as schematically illustrated in Fig. 2B, by providing dark pixels 26 around the dot pattern 9 such that the light in the FOI 25 is absorbed only by the dark pixels 26 and the dot pattern 9 appears.

[0084] The CGF 24 may have, for instance, a NIR CGF profile 33 as schematically illustrated in Fig. 3 such that wavelengths of about 700 nm up to about 1100 nm are transmitted.

[0085] As discussed above under reference of Fig. IB, the e-paper 21 may be moved up and down for allowing the estimation of the point spread function for different heights.

[0086] Fig. 4 schematically illustrates in a flow diagram an embodiment of a method 100 for estimating a point spread function, which is discussed in the following. The method 100 may be performed by the point spread function estimation system as described herein.

[0087] At 101, a dot pattern is presented on an electronic visual display, as discussed herein.

[0088] At 102, a part of the light originating from the dot pattern presented on the electronic visual display is filtered by a color glass filter such that a predetermined wavelength band is transmitted through the colored glass filter and incident on a camera, as discussed herein.

[0089] At 103, an image is captured with a camera which is arranged to detect the part of the light originating from the dot pattern presented on the electronic visual display, as discussed herein.

[0090] At 104, a dark image is captured with the camera, as discussed herein.

[0091] At 105, the point spread function of the camera is estimated based on the captured image and the captured dark image, as discussed herein.

[0092] Fig. 5 schematically illustrates in a flow diagram an embodiment of a method 200 for estimating a point spread function, which is discussed in the following.

[0093] The method 200 may be performed by the point spread function estimation system as described herein.

[0094] At 201, an electronic visual display is moved in at least one direction with respect to a camera to a plurality of different positions, as discussed herein.

[0095] As mentioned above, in particular, if the electronic visual display is too small to cover the whole FOV of the camera, the electronic visual display may be moved around to cover the whole FOV. Otherwise, in some embodiments, there may be no need to move the electronic visual display.

[0096] At 202, a dot pattern is presented on the electronic visual display at each of the plurality of different positions, as discussed herein.

[0097] At 203, a part of the light originating from the dot pattern presented on the electronic visual display is filtered by a colored glass filter such that a predetermined wavelength band is transmitted through the colored glass filter and incident on the camera, as discussed herein.

[0098] At 204, for each position of the plurality of different positions, an image is captured with the camera which is arranged to detect the part of the light originating from the dot pattern presented on the electronic visual display, as discussed herein.

[0099] At 205, the point spread function of the camera is estimated for each position based on the corresponding captured image, as discussed herein. Returning to the general explanations, as discussed above, an improved electronic visual displaybased point spread function estimation system is proposed herein.

[0100] Generally, the accurate estimation of the point spread function of a camera may be useful for simulations of use cases and application scenarios.

[0101] Moreover, the accurate estimation of the point spread function of a camera in the NIR range may be useful for optimizing depth sensors which may operate in the NIR range.

[0102] The use of a colored glass filter eliminates the angle of incidence dependency of the point spread function which may be present in other optical filters.

[0103] It should be recognized that the embodiments describe methods with an exemplary ordering of method steps. The specific ordering of method steps is however given for illustrative purposes only and should not be construed as binding.

[0104] In so far as the embodiments of the disclosure described above are implemented, at least in part, using software-controlled data processing apparatus, it will be appreciated that a computer program providing such software control and a transmission, storage or other medium by which such a computer program is provided are envisaged as aspects of the present disclosure.

[0105] Note that the present technology can also be configured as described below.

[0106] (1) A point spread function estimation system, including: an electronic visual display configured to present a dot pattern; a camera arranged to detect a part of the light originating from the dot pattern presented on the electronic visual display, wherein the camera is configured to capture an image for estimating a point spread function of the camera; and a colored glass filter arranged and configured to filter the part of the light originating from the dot pattern presented on the electronic visual display such that a predetermined wavelength band is transmitted through the colored glass filter and incident on the camera.

[0107] (2) The point spread function estimation system of (1), wherein the electronic visual display is an organic light emitting diode display.

[0108] (3) The point spread function estimation system of (1) or (2), wherein the dot pattern includes aNxN block of dots, wherein N is an Integer and larger than one.

[0109] (4) The point spread function estimation system of (3), wherein N is based on the field-of- view of the camera and the distance between the camera and the electronic visual display. (5) The point spread function estimation system of anyone of (1) to (4), further including a holder configured to hold and move the electronic visual display in at least one direction with respect to the camera for presenting the dot pattern in a plurality of different positions.

[0110] (6) The point spread function estimation system of (5), wherein the camera is configured to capture, for each position of the plurality of different positions, an image for estimating the point spread function for each position.

[0111] (7) The point spread function estimation system of anyone of (1) or (3) to (6), wherein the electronic visual display is an electronic paper display, and wherein the point spread function estimation system further includes a broadband light source arranged to illuminate the electronic paper display, wherein the broadband light source has a light emission spectrum including at least a part of the visible light spectrum and a part of the near-infrared light spectrum.

[0112] (8) The point spread function estimation system of (7), wherein the predetermined wavelength band is a near-infrared wavelength band.

[0113] (9) The point spread function estimation system of anyone of (1) to (8), further including: an information processing device configured to estimate the point spread function of the camera based on the captured image.

[0114] (10) The point spread function estimation system of (9), wherein the information processing device is further configured to estimate the point spread function further based on a dark image captured by the camera.

[0115] (11) A method for estimating a point spread function, including: presenting a dot pattern on an electronic visual display; capturing an image with a camera arranged to detect a part of the light originating from the dot pattern presented on the electronic visual display; and filtering the part of the light originating from the dot pattern presented on the electronic visual display by a colored glass filter such that a predetermined wavelength band is transmitted through the colored glass filter and incident on the camera.

[0116] (12) The method of (11), including presenting the dot pattern on an organic light emitting diode display.

[0117] (13) The method of (11) or (12), wherein the dot pattern includes a NxN block of dots, wherein N is an Integer and larger than one. (14) The method of (13), wherein N is based on the field-of-view of the camera and the distance between the camera and the electronic visual display.

[0118] (15) The method of anyone of (11) to (15), including moving the electronic visual display in at least one direction with respect to the camera for presenting the dot pattern in a plurality of different positions.

[0119] (16) The method of (15), including capturing, for each position of the plurality of different positions, an image for estimating the point spread function for each position.

[0120] (17) The method of anyone of (11) or (13) to (16), including: presenting the dot pattern on an electronic paper display; and illuminating the electronic paper display with a broadband light source, wherein the broadband light source has a light emission spectrum including at least a part of the visible light spectrum and a part of the near-infrared light spectrum.

[0121] (18) The method of (17), wherein the predetermined wavelength band is a near-infrared wavelength band. (19) The method of anyone of (11) to (18), including estimating the point spread function of the camera based on the captured image.

[0122] (20) The method of (19), including estimating the point spread function further based on a dark image captured by the camera.

Claims

CLAIMS1. A point spread function estimation system, comprising: an electronic visual display configured to present a dot pattern; a camera arranged to detect a part of the light originating from the dot pattern presented on the electronic visual display, wherein the camera is configured to capture an image for estimating a point spread function of the camera; and a colored glass filter arranged and configured to filter the part of the light originating from the dot pattern presented on the electronic visual display such that a predetermined wavelength band is transmitted through the colored glass filter and incident on the camera.

2. The point spread function estimation system of claim 1, wherein the electronic visual display is an organic light emitting diode display.

3. The point spread function estimation system of claim 1, wherein the dot pattern includes aNxN block of dots, wherein N is an Integer and larger than one.

4. The point spread function estimation system of claim 3, wherein N is based on the field- of-view of the camera and the distance between the camera and the electronic visual display.

5. The point spread function estimation system of claim 1, further comprising a holder configured to hold and move the electronic visual display in at least one direction with respect to the camera for presenting the dot pattern in a plurality of different positions.

6. The point spread function estimation system of claim 5, wherein the camera is configured to capture, for each position of the plurality of different positions, an image for estimating the point spread function for each position.

7. The point spread function estimation system of claim 1, wherein the electronic visual display is an electronic paper display, and wherein the point spread function estimation system further comprises a broadband light source arranged to illuminate the electronic paper display, wherein the broadband light source has a light emission spectrum including at least a part of the visible light spectrum and a part of the near-infrared light spectrum.

8. The point spread function estimation system of claim 7, wherein the predetermined wavelength band is a near-infrared wavelength band.

9. The point spread function estimation system of claim 1, further comprising: an information processing device configured to estimate the point spread function of the camera based on the captured image.

10. The point spread function estimation system of claim 9, wherein the information processing device is further configured to estimate the point spread function further based on a dark image captured by the camera.

11. A method for estimating a point spread function, comprising: presenting a dot pattern on an electronic visual display; capturing an image with a camera arranged to detect a part of the light originating from the dot pattern presented on the electronic visual display; and filtering the part of the light originating from the dot pattern presented on the electronic visual display by a colored glass filter such that a predetermined wavelength band is transmitted through the colored glass filter and incident on the camera.

12. The method of claim 11, comprising presenting the dot pattern on an organic light emitting diode display.

13. The method of claim 11 , wherein the dot pattern includes a NxN block of dots, wherein N is an Integer and larger than one.

14. The method of claim 13, wherein N is based on the field-of-view of the camera and the distance between the camera and the electronic visual display.

15. The method of claim 11, comprising moving the electronic visual display in at least one direction with respect to the camera for presenting the dot pattern in a plurality of different positions.

16. The method of claim 15, comprising capturing, for each position of the plurality of different positions, an image for estimating the point spread function for each position.

17. The method of claim 11, comprising: presenting the dot pattern on an electronic paper display; and illuminating the electronic paper display with a broadband light source, wherein the broadband light source has a light emission spectrum including at least a part of the visible light spectrum and a part of the near-infrared light spectrum.

18. The method of claim 17, wherein the predetermined wavelength band is a near-infrared wavelength band.

19. The method of claim 11, comprising estimating the point spread function of the camera based on the captured image.

20. The method of claim 19, comprising estimating the point spread function further based on a dark image captured by the camera.

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