GB2564850A

GB2564850A - Apparatus and method of light field display

Info

Publication number: GB2564850A
Application number: GB1711566.8A
Authority: GB
Inventors: Tan Baolin; Lu Min; Kang Jianghui; Ma Xiaoqi
Original assignee: Shenzhen Yinglun Tech Ltd; Euro Electronics Uk Ltd
Current assignee: Shenzhen Yinglun Tech Ltd; Euro Electronics Uk Ltd
Priority date: 2017-07-18
Filing date: 2017-07-18
Publication date: 2019-01-30
Also published as: GB201711566D0

Abstract

A scanning enhanced resolution light field display 1 comprising a liquid crystal microlens array 3 with a tunable focal length and an adjustable optical axis mounted at a separation distance g from the display screen 2, a high refresh rate screen whose pixels have a small light emitting part, a high speed signal processor 4 to check the sequence of time intervals of one period, transfer the sequence times to the controller of the liquid crystal microlens array 3, and render the corresponding images to the time intervals wherein the light field display uses time division multiplexing to increase the 3D image resolution in project space. The light field image may be a an integrated image of discrete images in different time intervals of one working period and the increasing times of its resolution are decided by the scanning times. The liquid crystal microlens array may be spherical lenslets 5 in hexagonal or a square arrangement and composed of two substrates (6, fig. 2), two alignment layers (8, 10 fig. 2) and two electrodes (7,11 fig. 2).

Description

This invention relates to a scanning light field display apparatus to enhance the resolution. More particularly this present invention relates to a dynamic liquid crystal (LC) microlens array with an adjustable optical axis and a controllable focal length, a high refresh rate screen with special designed pixels and a signal processing system.

The light field display is a potential major direction of the future three-dimensional (3D) image displays. Compared with the current binocular disparity autostereoscopic display, the light field display can avoid the accommodation-vergence conflict, and provide the viewers with more comfortable vision. It can be widely used in a lot of fields, such as VR/AR, the family amusement, the education, the advertising and the science etc. Hence, the light field display has the widespread commercial value and the prospects of development.

A light field display can be simply implemented by a display screen with a microlens array/pinhole array and a corresponding signal processing system which receives extensive attention. But some existing problems limit the development of this technology and its commercialization. The physical characteristics of the traditional microlens array/pinhole array introduce the trade-off between the spatial resolution and the angular resolution of this kind of light field display. Here, the spatial resolution determines the effective resolution of a display which affects the 3D image quality, while the angular resolution means the amount of the light ray passing, and determines the 3D viewing angle of a display. To a certain display screen, increasing the spatial resolution leads to the reduction of the angular resolution. On the contrary, increasing the angular resolution results in the lower spatial resolution.

This invention providing a solution to overcome this limitation- is to use an adjustable LC microlens array to replace the traditional optical instrument. Because a traditional microlens lenslet has unadjustable optical axis, only one of the light rays projecting from a certain

-2display pixel through the corresponding microlens lenslet can be used to restructure the original 3D scene. In this invention, the adjustable optical axis can lead to more than one light ray projecting from a display pixel to restructure the 3D scene. Because the optical axis of a lenslet can have only one direction at one moment, the scanning display method is introduced to cooperate with the adjustable microlens.

This present invention provides a solution to enhance the space resolution of a light field display without reducing the angular resolution. Here, there are several problems to solve to get a higher resolution 3D light field display. The first problem is how to adjust the optical axis of microlens lenslet to project the pixels to the required spatial position. The second problem is how to design the pixels of a display to satisfy the requirement of this scanning display. The third problem is how to render the corresponding elemental image in different scan intervals and different periods.

Statements of invention

This present invention implements a scanning enhanced-resolution light field display by projecting light rays of a pixel from more than one direction to different spatial positions to restructure the original 3D scene. The scanning method is used to project different light rays in different working intervals. The whole restructured 3D scene is an integrated image perceived and interpreted by discrete images due to eye persistence.

This present invention comprises a high refresh rate screen with a liquid crystal microlens array and a signal processor. The liquid crystal microlens array has X* Klenslet; here, Xand K are the numbers of the lenslet along the horizontal and vertical directions. Each lenslet can cover A *B display pixels which is named as the elemental image.

The adjustable microlens array, as the main optical instrument in this invention, is implemented by using an LC as the lens material. The structure of an LC microlens array is the LC material sandwiched between two substrates which are coated with two groups of electrodes and surface alignment layers. When the electric field caused by the voltage difference between the top and bottom electrodes is acting on the LC layer, the orientation of LC directors will be altered. The difference of the LC directors leads to the lens-like effect. The alteration of the electric field can change the focal length and the optical axis of this kind of lens.

In this present invention, the top electrode uses N arcs to form a whole circle instead of the traditional circle electrode. Here, each arc is a segment of the whole circle, and has the same shape and size. Due to this arrangement, slightly different voltages can be put on different arc electrodes, which can produce a slightly uneven electric field to rotate the optical axis. Different voltage can also lead to different refractive index of lens. Hence, the optical axis of a lens is rotatable, and the focal length is adjustable.

The pixels of a display screen must be redesigned to enhance the resolution by the scanning method. As is well known, a pixel is composed of the light emitting part and the black mask area. The light emitting part of a normal pixel is the main part, and the size of a pixel can be roughly equal to the size of the light emitting part. But in this invention, the size of the light emitting part is reduced, and the black mask area is increased. Here, the size of a pixel isn’t changed, but the light emitting part of a pixel is only a fraction of the normal one, and is determined by the scan frequency. On the contrary, the black mask part is enlarged to several times the size of the new light emitting part. If this 3D display will scan I times along the horizontal direction and J times along the vertical direction, the size of the new pixel’s light emitting part is P_x PX\ . J. Here, P_x and P_y are the width and the length of a normal pixel. This makes the black mask of a pixel increase. Now, the resolution of a 3D restructured scene is /x J times of the traditional light field display. A detailed example will show how to implement this method in next section.

The element images to represent the 3D image must be re-rendered according to the scanning frequency. Here, a working period means the time spent on restructuring one 3D scene, and a working period includes /x J scanning intervals. In each scanning interval, the scanning light field display will project a group of XxKelement images; here, Xand F are the numbers of the lenslet along the horizontal and vertical directions. Hence, the signal processing system should render /x J groups of element images in one working period, and send the corresponding group of element images to the display in the (i*j)^th interval, where l<i<I, After one working period, a whole 3D scene can be represented due to the

-4persistence of vision. Compared with the traditional light field display whose spatial resolution is the number of the microlens lenslet, the spatial resolution of this present invention is enhanced by IxJ times which means much higher definition 3D scene is represented.

The working process of a scanning light field display is described as the following: firstly, the basic voltage is put on each arc electrode of the LC microlens to decide the basic state of the microlens (the focal length, the refractive index etc.), and the optical axis is normal to the lens surface; secondly, the optical axis is rotated by slightly increasing the voltage of one arc electrode; thirdly, the signal processing system processes the corresponding group of element images and sends them to the display; fourthly, the display projects them to the desired spatial position by the microlens array; fifthly, the optical axis is rotated to the next position by slightly changing the voltage of another arc electrode; repeat steps 2 to 4 to complete a working period.

The scanning method to enhance the resolution is based on the eye persistence of human being. Hence, one working period must be shorter than the persistence time of the human eye. To get a high visual enjoyment, one working period should be less than l/65s, so a high refresh rate display screen is necessary for this light field display.

Compared with the traditional light field display, the present invention can display higher resolution 3D light field image. The multiple of the enhanced resolution is decided by the scanning times. More scanning times result in the smaller light emitting parts and the higher resolution.

Detailed Description of the Invention

An example light field display of the present invention will be described by referring to the accompanying figures in which:

Figure lisa schematic diagram of a scanning enhanced-resolution light field display; Figure 2 is a schematic diagram of the structure of an LC microlens;

Figure 3 is a schematic diagram of the 2^nd electrode of a traditional LC microlens;

-5 Figure 4 is a schematic diagram of the 2^nd electrode of the LC microlens used in this invention;

Figure 5 is a schematic diagram of the optical axis of an LC microlens lenslet;

Figure 6 is a schematic diagram of the rearranged and redesigned display pixels;

Figure 7 is a schematic diagram of an LC microlens lenslet and its corresponding display pixels;

Figure 8 is a schematic diagram to show the viewing effect of the adjacent pixels in two time intervals of one working period;

Figure 9 is a schematic diagram of the projected image after one working period;

Figure 10 is the working flow of the light field display.

Figure 1 shows an embodiment of an enhanced resolution scanning light field display 1 with a tunable LC microlens array 3. This light field display 1 is composed of a display screen 2, a tunable LC microlens array 3 and a signal processor 4. The tunable LC microlens array 3 has XxL lenslets 5. In this embodiment, the optical axis of each lenslet 5 moves twice in a row, then moves another twice in the next row, so the scanning mode is 2^2, which means 1=2 and J=2.

Figure 2 shows the structure of an LC microlens 3. This LC microlens array 3 is composed of two coated substrates 6 with two electrodes (the 1st electrode 7 and the 2nd electrode

11), two alignment layers (the 1st alignment layer 8 and the 2nd alignment layer 10), and the sandwiched LC layer 9. Here, the two alignment layers 8 and 10 are not necessary due to the different LC material used.

Figure 3 shows the whole circle electrode 12 as the 2nd electrode 11. When the 2nd electrode 11 was designed as a circle shape 12, the focal length of this microlens 3 was tunable by changing the voltage, but its optical axis was fixed.

Figure 4 shows the shape of the 2^nd electrode 11 used in this invention. For the convenience of the description, it is only shown that the 2^nd electrode 11 is composed of four arc electrodes 13 (electrodes I, II, III and IV) shaped like a circle. Here, N=4. As is shown in the figure, the voltage of each arc electrode 13 is tunable and can have different value.

-6Figure 5 shows the alterations of the optical axis of an LC microlens lenslet 5 in four intervals of one working period. The optical axis can be adjusted by increasing the voltage of one arc electrode 13. Before the light field display begins working, an initial voltage Vo will be put on the arc electrodes 13, and the optical axis is at the position Po. In the 1^st time interval of a working period, slightly increasing the voltage on the arc electrode 113 results in rotating the optical axis to the position Pi. Then, the optical axis can be adjusted to the position Pn by increasing the voltage of the arc electrode II13 in the 2^nd time interval. In the 3^rd time interval, the optical axis is adjusted to the position Pin by increasing the voltage of the arc electrode III 13. In the 4^th time interval, the optical axis is adjusted to the final positon Piv by increasing the voltage of the arc electrode IV 13. After it, returning the voltages on the arc electrodes II, III and IV makes the optical axis back to the position Pi, and the next working period starts.

As discussed before, the light emitting part of the display’s pixel 14 should be redesigned to satisfy the requirements of the scanning display. Figure 6 shows the new display pixels 14, here the subpixels 15 of a pixel are Red, Green, and Blue (RGB). According to the display screen 2 used, the subpixels 15 can also be composed of other colours, such as Red, Green, Blue and Yellow (RGBY). In this embodiment, the scanning mode is 2x2 (1=2 and J=2), so the size of a pixel is P_x*P_y, and the size of the light emitting part 15 is Px/2*P_y/2. Compared with the normal pixels 14, the new pixels 14 have a smaller light emitting part 15 and a bigger black mask area 16. In one of the working time intervals, the light emitting part 15 and the black mask area 16 will be projected to the desired spatial position together, and the image viewed is discrete. But the light emitting part 15 can be projected to different area because of the rotation of the optical axis, and cover the project area of the black mask

16. After one working period of scanning, the image watched by a viewer is an integrated whole image due to the eye persistence.

Figure 7 is a schematic diagram of a LC microlens lenslet 5 and its corresponding display pixels 14. In this embodiment, each lenslet 5 can cover 10*10 pixels 14 which is named as the elemental image 17. Here, the size of an elemental image is 10P_x*10P_y. The microlens array 3 is mounted on the display screen 2, and the distance between them is g. According to the light field display mode, g can be equal to the focal length/ or bigger than it, or smaller than it.

Figure 8 shows the projected image of the adjacent display pixels 14 after two time intervals of one working period. For the convenience of description, only the adjacent display pixels 14 along one dimension are shown. In the 1^st interval, the optical axis of the lenslet 5 is at the 1^st position, and the pixels 14 A and B are projected to the projected space 18 Al and Bl, respectively. Here, the projected space 18 is s far away from the lenslet 5. In the 2^ndinterval, the optical axis of lenslet 5 is rotated to 2^nd positon, and the pixels 14 A and B are projected to the new positions 18 A2 aa&B2. Figure 8 shows there is no black mask area 16 between the projected image 18 along this direction after two intervals. Now, the discrete pixels 14 are integrated into a whole image 18 due to the eye persistence. The rotating angle a between the optical axis 1 and 2 is a = arctan(P_y/2g'). The relationship among the object distance g, the image distance 5 and the focal length f of the lenslet 5 is based on the

1 principle of lens imaging satisfies - + -= 1//.

^s

Figure 9 shows how the discrete light emitting parts integrate into a whole image after one working period. For convenience, a sample as 3*3 display pixels 14 is shown, and the number 1, 2, 3 and 4 mean the scanning times. Here, the block frame means a designed display pixel 14. In one working period, the light field display 1 projects the light emitting part of display pixels 14 to the 1^st position, then the 2^nd and 3^rd positons, finally the 4^thposition. In these four time intervals, the signal processor 4 presents the original high definition 3D scene to X* Y element images, and each element image has 20*20 pixels. These 20*20 pixels are divided to 10*10 groups, and each group has 2*2 adjacent pixels. The signal processor 4 will transfer these 2*2 pixels clockwisely from the left top pixel one by one in the four time intervals. After one period, the projected image pixels 18 of this 3*3 display pixels 14 are 6*6 and forms an integrated image. Now, the resolution is 4 times of the original one, which means the resolution is enhanced by this scanning method after one working period.

Figure 10 shows the working flow of this light field display 1 in one working period. The signal processor 4 prepares the image for the 1^st interval, and the counter n is set as n=l.

-8Adjusting the voltage of the 1^st arc electrode makes the rotation of the optical axis. After the optical axis reaches its 1^st position, the light field display projects the prepared image of 1^st interval. Then the counter n is increased by 1, and the optical axis is rotated a horizontal angle a = arctan(Px/2g) by slightly adjusting the voltages of the 2^nd arc electrodes. At the same moment, the signal processor 4 prepares the image for the 2^ndinterval. The prepared image is projected when the optical axis reaches its 2^nd position. After it, the counter n is set to 3, and the optical axis is rotated a vertical angle a = arctan^Py/2g) by adjusting the 3^rd arc electrode while the signal processor 4 prepares the image of the 3^rd interval. The image is projected when the optical axis reaches it desired 3^rdposition. Finally, the counter n is increased to 4, and the optical axis is rotated a horizontal angle a = arctan(Px/2g) by adjusting the 4^th arc electrode while the signal processor 4 prepares the image of the 4^th interval. After projecting the image of the 4^th interval, reducing the voltages on 2^nd, 3^rd and 4^th arc electrodes makes the optical axis return to its 1^st position and be ready for the next working period.

Claims

1 A scanning enhanced-resolution light field display comprising: a liquid crystal microlens array with a tunable focal length and an adjustable optical axis mounted at a separation distance from the display screen; a high refresh rate screen whose pixels have a small light emitting part; a high-speed signal processor to check the sequence of the time intervals of one period, transfer the sequence times to the controller of the liquid crystal microlens array, and render the corresponding images to the time intervals; and a scanning enhancedresolution light field display being such that:

the scanning light field display uses time division multiplexing method to increase the 3D image resolution in project space by projecting different parts of original high definition 3D scene in the corresponding time intervals of a working period;

the signal processor presents the original high definition 3D scene to ΑΛχΤ element images for the corresponding Χχ Ymicrolens lenslets, each elemental image has IA'.JB pixels and will be divided to A *B groups of sub element images, each sub element image has /x J pixels, here, a microlens lenslet can cover A*B display pixels;

the signal processor renders and transfers the fxJ pixels of each sub element image sequentially infxJtime intervals of a working period, it also processes and transfers the data for Χχ T element images synchronously in one time interval.

2 The device as claimed in claim 1, wherein the 3D light field image shown in the project space is an integrated image of the discrete images in different time intervals of one working period, and the increasing times of its resolution are decided by the scanning times.

3 The device as claimed in claim 1, wherein the tunable liquid crystal microlens array whose spherical lenslets are in the hexagonal or square arrangement is composed of two substrates, two alignment layers and two electrodes, where, the 2nd circle electrode is formed by the discrete arc electrodes which can be put on different voltage to rotate the optical axis and adjust the focal length.

4 The device as claimed in claim 1, wherein the size of each display screen’s pixel is the same as the normal ones, but its light emitting part surrounded by the enlarged black mask

- 10 areas is placed at the left top corner of the pixel, whose size is only a fraction of the normal one (7//x 1/J of the normal one), and decided by the scanning mode and the scanning times; the black mask areas of the pixels can be the major part of a pixel in the case.

5 The device as claimed in claim 1, wherein the signal processor processes the original high resolution image to render different group of images for the corresponding time interval of a working period; the order of each time interval is returned to the liquid crystal microlens to control the voltages of the arch electrodes which is used to adjust its optical axis and focal length.