Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
  • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
  • G02F1/1333—Constructional arrangements; Manufacturing methods
  • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B30/00—Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images
  • G02B30/20—Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images by providing first and second parallax images to an observer's left and right eyes
  • G02B30/26—Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images by providing first and second parallax images to an observer's left and right eyes of the autostereoscopic type
  • G02B30/27—Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images by providing first and second parallax images to an observer's left and right eyes of the autostereoscopic type involving lenticular arrays
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B30/00—Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images
  • G02B30/20—Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images by providing first and second parallax images to an observer's left and right eyes
  • G02B30/34—Stereoscopes providing a stereoscopic pair of separated images corresponding to parallactically displaced views of the same object, e.g. 3D slide viewers
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B5/00—Optical elements other than lenses
  • G02B5/30—Polarising elements
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N13/00—Stereoscopic video systems; Multi-view video systems; Details thereof
  • H04N13/30—Image reproducers
  • H04N13/302—Image reproducers for viewing without the aid of special glasses, i.e. using autostereoscopic displays
  • H04N13/305—Image reproducers for viewing without the aid of special glasses, i.e. using autostereoscopic displays using lenticular lenses, e.g. arrangements of cylindrical lenses
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
  • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
  • G02F1/1333—Constructional arrangements; Manufacturing methods
  • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
  • G02F1/133526—Lenses, e.g. microlenses or Fresnel lenses

Definitions

• the present invention relates to display devices, and in particular to display devices adapted to display three dimensional or stereoscopic images.
• a display device is capable of providing a different view to the left and the right eye of a user of the display device. This can be achieved by providing a separate image directly to each eye of the user by use of specially constructed goggles.
• a display provides alternating left and right views in a time sequential manner, which views are admitted to a corresponding eye of the viewer by synchronised viewing goggles.
• time sequential synchronisation of left and right eye views is provided by way of a spatial modulation element in the form of an LCD panel which alternately occludes left and right eye views of a display using parallax.
• the system of US '807 has to constantly track the position of the viewer relative to the display device.
• the present invention relates to classes of display devices where different views of an image can be seen according to the viewing angle relative to a single display panel without necessarily requiring tracking of user position.
• these will be referred to generally as 3D display devices.
• One known class of such 3D display devices is the liquid crystal display in which the parallax barrier approach is implemented.
• a display device 100 of the parallax barrier type comprises a back panel 11 that provides a plurality of discrete light sources.
• the back panel 11 may be formed by way of an areal light source 12 (such as a photoluminescent panel) covered with an opaque mask or barrier layer 13 having a plurality of slits 14a to 14d distributed across its surface. Each of the slits 14 then acts as a line source of light.
• a liquid crystal display panel (LCD) 15 comprises a plurality of pixels (eg. numbered 1 to 10 in figure 1) which are separately addressable by electrical signals according to known techniques in order to vary their respective light transmission characteristics.
• the back panel 11 is closely positioned with respect to the LCD panel 15 such that each of the line sources 14 of light corresponds to a group 16 of pixels.
• pixels 1 to 5 shown as group 16 ⁇ correspond to slit 14a
• pixels 6 to 10 shown as group 16 2 correspond to slit 14b
• Each pixel of a group 16 of pixels corresponds to one view V of a plurality of possible views (V_ 2 , V_- ⁇ , Vo, ⁇ , V 2 ) of an image such that the respective line source 14a can be viewed through one of the pixels 1 to 5 corresponding to that view.
• the number of pixels in each group 16 determines the number of views of an image present, which is five in the arrangement shown. The larger the number of views, the more realistic the 3D effect becomes and the more oblique viewing angles are provided.
• the 'image' being displayed as the overall image being generated by all pixels in the display panel, which image is made up of a plurality of 'views' as determined by the particular viewing angle.
• the brightness of any given discrete light source 14 as perceived by the viewer will be a function of the size of the pixel lying between the light source and the viewer in a direction orthogonal to the light beam.
• the angular size of view of the light source 14a as viewed through pixel 3 of figure 1 is greater than the angular size of view of light source 14a as viewed through pixel 5. Therefore, the perceived intensity of the viewed source will be a function of viewing angle.
• the present invention provides a display device for displaying a three dimensional image such that different views are displayed according to the viewing angle
• the display device including: a display panel having a plurality of separately addressable pixels for displaying said image, the pixels being grouped such that different pixels in a group correspond to different views of the image, each pixel in a group being positioned relative to a respective discrete light source; a display driver for controlling an optical characteristic of each pixel to generate an image according to received image data; and an intensity compensation device for further controlling said optical characteristic of pixels within a group to compensate for an angular size of view, of the respective light source, via said pixels.
• the present invention provides a method for displaying a three dimensional image on a display device such that different views of the image are displayed according to the viewing angle, the method comprising the steps of: processing image data to form pixel intensity data values for each one of a plurality of separately addressable pixels in display panel, the pixels being grouped such that different pixels in a group correspond to different views of the image, and each pixel in a group being positioned relative to a respective discrete light source, the pixel intensity data values each for controlling an optical characteristic of a respective pixel to generate the image; applying intensity correction values to at least some pixel data values within each group to compensate for an angular size of view, of the respective light source, via said pixels; and using the corrected pixel data values to drive pixels of the display panel to generate said image.
• Figure 1 shows a schematic cross-sectional view of an existing design of LCD device that uses the parallax barrier approach to display three dimensional images
• Figure 2 shows a schematic cross-sectional diagram useful in illustrating the geometry of a parallax barrier LCD device
• Figure 3 shows a schematic diagram illustrating the angular width of each view of a light source as determined by left and right edges of pixels through which the light source is viewed
• Figure 4 shows a graph of normalised brightness as a function of pixel number for a group of pixels providing different views of an image
• Figure 5 shows a graph of brightness correction factors to be applied to each pixel of a group of pixels providing different views of an image
• Figure 6 shows a graph of width of view and angular location as a function of view number
• Figure 7 shows a schematic block diagram of a display device according to embodiments of the present invention
• Figure 8 shows an embodiment of the invention utilising a lenticular array
• Figure 9 shows a schematic block diagram of a display device according to embodiments of the present
• the invention uses a display panel 15 having a plurality of separately addressable pixels 1...10, in which the pixels are grouped so that the different pixels 1...5 or 6...10 respectively in a group 16 1 and 16 2 correspond to different views of the image.
• the display panel 15 may be any suitable electro-optical device in which an optical characteristic of each pixel can be varied according to an electrical control signal to generate an image.
• the display panel is a liquid crystal display.
• An illumination source having a plurality of discrete light sources 14a ... 14d, so that each group 16 of pixels is positioned to receive light from a respective one of the light sources, is preferably provided.
• This may be by way of the areal light source 12 and mask 13 arrangement of figure 1 , but could also be provided by way of a pixellated light source providing light sources 14 as lines of pixels, individual pixels or blocks of pixels.
• the plurality of discrete light sources could be virtual light sources provided by way of a backlight and lens array (e.g. a lenticular sheet array) providing a series of high intensity light spots.
• a display device 80 includes an LCD panel 75, areal light source 72 and a lens array 71.
• the lens array focuses light from the areal source 72 into a plurality of discrete focal points 73 just outside the plane of the LCD panel so that each illuminates a plurality of pixels in the LCD panel, similar to that described in connection with figure 1.
• Part of a group of pixels in the display panel 15 is shown in figure 2.
• a light source 14 of width w corresponds with, and can be viewed through, a group of pixels 0...7 at respective viewing angles ⁇ o, ⁇ i, ... ⁇ 7 relative to the normal of the plane of the display panel. It will be understood that only approximately half of the pixel group 16 is shown, a further seven pixels being present to the left of pixel 0 to complete the pixel group 16.
• Each pixel has a width po, pi, ... pi.
• widths po-.p? are equal, but they could vary in order to compensate to a certain extent for the angle of incidence of light passing therethrough.
• the distance between the back panel illumination source 14 and the display panel 15 is shown as h.
• h 2.3 mm
• p 0 200 microns
• w 50 microns although these values may be varied significantly.
• Figure 3 shows that the angular size ⁇ of the viewing cone of each view Vo, V-i, V 2l V3, V 4 becomes smaller for higher n, where n is the pixel number counting from the pixel 0 that is centred over the light source 14 (see figure 2).
• each of the n views becomes less for higher values of n, assuming that the light source 14 is an isotropic emitter. This would normally be the case at least to the extend of angle subtended by the group 16 of pixels corresponding to the relevant light source 14. The observer will therefore experience a lower brightness for the more oblique views (e.g. V , V 3 ) than for the orthogonal view Vo. This results in some undesirable artefacts when observing the different views of the image being displayed.
• the number ⁇ determines the brightness of each view. If the light source 14 is an isotropic emitter, emitting equal intensity in all (relevant) directions, the brightness scales linearly with the angle each view subtends. If the brightness of view 0 is normalised to 1 , then the brightness for each view n is given by the expression:
• an intensity compensation device that controls the optical characteristic of each pixel 0...N and 0...-N in ao group 16 so as to compensate for the viewing angle.
• the intensity compensation device preferably substantially normalises an intensity of the light source 14 as displayed by a group 16 of pixels to that of the other pixels in the group for any given location in the display panel. The perceived intensity thereby becomes independent of the viewing angle.
• The5 intensity compensation device may take into account any degree of anisotropic behaviour of the light source 14. Different intensity correction factors will be required for different display types (e.g.
• Figure 7 shows schematically exemplary embodiments of a display device 101 incorporating an intensity compensation device.
• An image processor 50 receives a stream of image information including intensity pixel data for each of a plurality of views ⁇ o... ⁇ 7 -
• the image5 information is processed and stored into a frame buffer 51 in digital form so that it can be rendered onto a display device 53.
• Frame buffer 51 includes a plurality of pages 58, each page including the pixel data for a respective view,
• the frame buffer 51 is accessed by a display driver 52 that provideso appropriate drive voltage and/or current signals to each pixel of a display panel 53 in accordance with each of the stored values in frame store 51.
• a display driver 52 that provideso appropriate drive voltage and/or current signals to each pixel of a display panel 53 in accordance with each of the stored values in frame store 51.
• the application of intensity correction values by the intensity compensation device can be applied either: (i) by digitally modifying the image data stored in the frame store 515 to include a correction factor so that the value of drive parameter selected by the display driver 52 is suitably modified, or (ii) by leaving the image data stored in the frame store 51 unmodified, but applying a correction factor to the output of the display driver 52.0
• an intensity compensation device 60 (shown in dashed outline) is provided as, for example a look-up table accessible by the image processor 50.
• the look-up table comprises a plurality of pages 61 , 62, 63 of correction values, each page corresponding to one of the viewing angles ⁇ i... ⁇ 7 to be applied to image data received by the image processor.
• the image processor 50 obtains appropriate corrections to the image data and stores this compensated data in frame store 51.
• the expression 'correction values' in this context may include
• the look-up tables 61 - 63 may provide a substitution value x s (as a function of ⁇ ) to be stored in the frame store in place of xi.
• the look-up tables 61 - 63 may provide an offset value x 0 (as a function of ⁇ ) which is combined with the input value and the result Xi + x 0 stored in the frame store in place of Xj.
• the functions of the image processor 50 can be realised in software, and the functions of the intensity compensation device 60 can also be realised as a software implementation.
• the compensation device 60 may operate independently of the image processor 50 upon data already stored in the frame store 51 by the image processor 50. This can be effected by using a second access port 64 to the frame store 51.
• the compensation device 60 in this embodiment may also be implemented as a software module, without interfering with the operation of the image processor 50 (for example, where this is a customised graphics processor).
• the look-up tables 61 - 63 may provide a substitution value or an offset value to be implemented by the intensity compensation device.
• the intensity compensation for each pixel drive signal could be carried out in real time in the analogue domain, i.e. by applying a correction voltage offset to each pixel signal produced by the display driver 52.
• an intensity compensation device 70 is installed between the display driver 52 and the display panel 53 to apply specific offset voltages and/or currents to those output by the display driver.
• the intensity correction values may be considered as voltage and/or current offset values.
• a hybrid system could deploy both techniques of digital correction values applied to the frame store 51 by compensation device 60 and analogue offsets applied to the display driver outputs by compensation device 70. An appropriate contribution would be made by both, although this may be a more complicated solution.
• analogue offsets or correction values applied by the intensity compensation device 70 might be selected to move the operation of the display panel into an appropriate portion of a transmission-voltage characteristic, while digital correction values might be selected to compensate for differences in the slope of the transmission-voltage characteristic.
• the intensity compensation device 60 as described herein may also be applied in other forms of 3D display other than that shown in figures 1 and 2.
• the invention can also be applied to a lenticular 3D display device 200.
• a liquid crystal display panel 115 includes a plurality of pixels (ai to b 8 are shown) arranged in groups 116 ⁇ , 116 2 , in similar manner to that in figure 1.
• the lenticular array may include any sheet of corrugated optical material, or array of discrete or joined lenses to provide localised focusing for groups of pixels of the LCD panel.
• the width of each lens element is chosen to be eight pixels, corresponding to an eight-view 3D display. Of course, the width of each lens element may be chosen to correspond to different numbers of pixels according to the angular resolution required.
• the pixels ai to as of the LCD are imaged into the different views. For example, the light rays emitted from pixels a 2 and a 4 are shown.
• the rays emitted by pixel a 2 propagate to a large extent obliquely with respect to the rays emitted by pixel a .
• the angle between them is, on average, approximately equal to the angle between the two views ( ⁇ ).
• the dependence of the reflectivity on the angle of the plane of the pixel to the light source will still exist and can be corrected for using the intensity compensation device as described herein.
• the invention as described above also has important implications for the optimisation of liquid crystal displays generally.
• the viewing angle dependence of LCD panels is known generally to be rather poor.
• Figure 10 illustrates how contrast and grey scale inversion depends upon viewing angle for a standard 90 degree twisted nematic (TN) transmissive LCD without compensation foil.
• the horizontal viewing angle is shown on the x-axis between -60 degrees and +60 degrees from the normal to the plane of the display
• the vertical viewing angle is shown on the y-axis between -60 degrees and +60 degrees from the normal to the plane of the display.
• the orientations of the optical axes 90, 91 of the LCD polarisers and the optical axes 92 of the liquid crystal directors are shown in the lower part of the figure. From figure 10, it is seen that the image quality strongly depends upon viewing angle.
• the optimal viewing angles are represented by the diagonal line 94 running from top left to bottom right, and grey scale inversion occurs for viewing positions to the right and above the line 94.
• maximising performance for horizontal viewing directions is more important than maximising performance for vertical viewing directions.
• multiple viewers of a display device will normally be arranged with their eye levels more-or-less consistent relative to the screen (i.e. with very little variation along the y-axis), but their horizontal viewing angles relative to the x-axis may vary significantly.
• a user seated at a computer monitor is more likely to vary head position along the x-axis while working, than along the y-axis.
• the LCD would be rotated anticlockwise through 45 degrees from the orientation shown in figure 10, such that its polarisation axes are at approximately 45 degrees to the x- and y-axes of the display when in use.
• the performance of the display device is optimised for horizontal viewing angles, but is compromised for vertical viewing angles.
• 3D LCD displays suffer from the same problems with optimisation of viewing angle dependency in respect of x and y directions.
• optimisation of brightness rendering can be achieved by electronic techniques in driving the display, using the described intensity compensation device 60 and/or 70 as described above. Therefore, it is more appropriate to provide the display device with an orientation in which the inherent optical characteristics of the display panel are optimised for vertical viewing angle variations.
• the 3D display device described above is arranged so that, in normal use, it has the pixels within each group 16 that provide different views as a function of angle to a first axis of the display panel, and has the polarising elements of the display panel oriented so as to minimise viewing angle dependence relative to a second axis of the display, where the second axis is orthogonal to the first axis.
• the inherent optical characteristics of the display panel are such that viewing angle dependence is reduced or substantially minimised relative to the y-axis and the intensity compensation device 60 and/or 70 serves to reduce or substantially minimise viewing angle dependence relative to an axis that is transverse to the y-axis. More preferably, the intensity compensation device 60 and/or 70 serves to reduce or substantially minimise viewing angle dependence relative to an axis that is orthogonal to the y-axis (i.e. the x-axis).
• the x-axis is defined as the horizontal axis when the display is in normal use
• the y- axis is defined as the vertical axis when the display is in normal use.
• Other embodiments are intentionally within the scope of the accompanying claims.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Nonlinear Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Engineering & Computer Science (AREA)
• Mathematical Physics (AREA)
• Chemical & Material Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Control Of Indicators Other Than Cathode Ray Tubes (AREA)
• Liquid Crystal Display Device Control (AREA)
• Testing, Inspecting, Measuring Of Stereoscopic Televisions And Televisions (AREA)
• Television Receiver Circuits (AREA)

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• 2003
  • 2003-10-04 GB GBGB0323283.2A patent/GB0323283D0/en not_active Ceased
• 2004
  • 2004-09-30 DE DE602004012129T patent/DE602004012129T2/de not_active Expired - Lifetime
  • 2004-09-30 KR KR1020067006463A patent/KR101112059B1/ko not_active Expired - Fee Related
  • 2004-09-30 WO PCT/IB2004/051928 patent/WO2005033776A1/en not_active Ceased
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  • 2004-09-30 AT AT04770136T patent/ATE387644T1/de not_active IP Right Cessation
  • 2004-09-30 EP EP04770136A patent/EP1673652B1/en not_active Expired - Lifetime
  • 2004-09-30 US US10/574,140 patent/US20070040778A1/en not_active Abandoned
  • 2004-09-30 CN CN2004800288916A patent/CN1864089B/zh not_active Expired - Fee Related
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