GB2604385A

GB2604385A - Back-lit screens

Info

Publication number: GB2604385A
Application number: GB2103059.8A
Authority: GB
Inventors: Paul Alexander Geissler Michael
Original assignee: Mo Sys Engineering Ltd
Current assignee: Mo Sys Engineering Ltd
Priority date: 2021-03-04
Filing date: 2021-03-04
Publication date: 2022-09-07
Also published as: GB202103059D0

Abstract

A back-lit screen comprises a rigid frame 12 extending around the periphery of the screen which defines an opening and a translucent sheet 11 extending across the opening. The frame is configured so that the sheet meets the frame at an apex 15 of the frame so that the screen appears frameless or borderless. The sheet is preferably fixed to the frame in a recess provided in an outer face of the frame. Illumination means 16 are provided to illuminate the sheet, the illumination means preferably comprising red, green and blue LEDs which are controllable to yield any desired colour. Multiple screens may be located adjacent to one another with the sheets of each being coplanar.

Description

BACK-LIT SCREENS

This invention relates to back-lit screens.

Back-lit screens are used for purposes such as exhibition stands. A typical back-lit screen comprises a structural frame with a sheet of translucent material supported by the frame. One or more lamps illuminate the rear of the screen; that is the side opposite the side at which the intended viewer is to be located. Because the sheet material is translucent, and not transparent, light from the lamps passes through the sheet material and is scattered by it so that a viewer at the front of the screen sees the screen as having a somewhat uniform overall luminance. The screen may be of a uniform colour or it may bear messaging. When the screen is acting as a backdrop for an exhibition stand it may bear logos and other promotional words and images.

Sometimes multiple individual back-lit screens are arranged next to each other to form a composite back-lit screen. This may happen when the overall size of the required screen is larger than individual screens that are available or when the screen is required to have a non-planar shape. For example, a composite screen may be composed of three planar walls arranged to form a back-lit bay. Figure 1 shows a cross-section on a horizontal plane at the meeting point of two individual screens. Each individual screen comprises a frame 1 which supports a translucent sheet 2. Lamps 3 are disposed behind each sheet. A problem with composite screens of this type is that typically the illumination of the composite screen is irregular at the meeting point of the individual screens. The meeting point may be a location where one planar screen is angled relative to an adjacent planar screen, forming a corner. The frame 1 of each screen extends laterally beyond the sheet 2 of the screen as indicated at 4. And there is a region 5 of the frame against which the sheet 2 is tensioned which obstructs light from the respective lamp(s). This results in a region 4 along the meeting point of the individual screens where no light from the lamps 3 passes through the screen. As a result, the overall illumination from the screen to a viewer is non-uniform. Typically, there is a dark stripe or shadow line at the meeting point of the screens. 1.

This is unsightly when the back-lit screen is being used for promotional purposes. When the back-lit screen is being used as a chroma key background, dark stripes of this nature can interfere with the chroma-keying process. For chroma keying, the screen may be illuminated with light of a predetermined and/or uniform colour. The colour may, for example, be green or blue.

There is a need for an improved back-lit screen.

According to one aspect there is provided a back-lit screen comprising a rigid frame extending around the periphery of the screen and having a front face, the front face having an interior face which defines an opening, and an outer face which defines the exterior contour of the frame transversely to the opening. There is a translucent sheet extending across the opening. The frame is configured so that over at least a part of the periphery of the screen the forward-most part of the interior face is coincident with the exterior contour of the frame.

The translucent sheet may bear on the forward-most part of the frame to extend across the opening.

The translucent sheet may be flexible and may be secured to the frame in a recess on the outer face of the frame.

The frame may comprise a plurality of linear elements joined together to define the opening.

The back-lit screen may comprise an illuminator located behind the sheet for shining light through the sheet.

The illuminator may be carried by the frame.

The illuminator may be elongate and may extend along at least a part of the frame for preferentially illuminating a peripheral portion of the sheet.

The illuminator may be controllable to vary the colour of light emitted therefrom.

There is provided a composite back-lit screen comprising a plurality of individual backlit screens located adjacent to each other.

The individual back-lit screens may be located adjacent to each other such that a forward-most part of one of the screens is located adjacent a forward-most part of another of the screens.

The individual back-lit screens may be located adjacent to each other such that their respective translucent sheets are coplanar.

The composite back-lit screen may comprise a controller for independently controlling the colour and/or intensity of illuminators located to shine light through respective ones of the individual screens.

The present invention will now be described by way of example with reference to the accompanying drawings.

In the drawings: Figure 1 is a cross-section through a prior art back-lit screen.

Figure 2 is a cross-section through components of a back-lit screen.

Figure 3 shows the components of figure 3 assembled.

Figure 4 is a front view of a screen formed from the components of figure 2.

Figures 5 and 6 show alternative mechanisms for attaching a sheet to a frame.

Figure 7 shows a composite back-lit screen.

Figure 8 shows two screens arranged adjacent each other in a non-coplanar configuration.

In the present document the term "back-lit" screen refers to a screen having a frame supporting a translucent sheet irrespective of whether that screen is presently being back-lit.

Figure 2 shows components for a back-lit screen. The components comprise a screen element and a frame element. The screen element comprises a translucent sheet 11. Only part of the sheet is shown in figure 2. At the edges of the sheet are one or more mounting blocks 10 which are attached to the sheet, e.g., by adhesive or mechanical grippers. The mounting block(s) is/are rigid or semi-rigid. It/they may, for example, be polymer block(s) or strip(s). The sheet is flexible. The sheet is translucent and hence not transparent. The sheet is capable of diffusing light passing through it. The sheet may be elastic so that it can be stretched into a taut configuration. This can help to make it planar in the resulting screen.

The frame element comprises a rigid structure 12. Structure 12 extends out of the plane of figure 2 to form a linear or curved side of a frame, as illustrated in figure 4. Multiple such structures can be attached together, e.g., by corner blocks or fishplates, to form a multi-sided frame, again as shown in figure 4. The frame structure 12 has an interior surface 14 which is to face the interior of the frame when assembled. The interior surface is angled so that the frame structure tapers to a point 15 at its end that is to face the front of the frame when assembled. On the exterior surface of the frame structure is a recess 13. The recess 13 is sized to receive the mounting block(s) of the screen element.

Figure 3 shows the components of figure 2 assembled. The mounting block(s) is/are inserted in the recess 13 on the exterior surface of the frame structure 12. This anchor the edge of the translucent sheet 11 to the frame structure. The sheet 11 extends from the mounting block(s) around the pointed tip 15 of the frame structure. From there it extends across the frame to another piece of frame structure, as shown in figure 4.

One or more illuminator lamps 16 are located behind the sheet, so as to shine light through the sheet. Because the frame structure tapers to a point at its forward-most tip, light from the illuminator lamp(s) can reach substantially the entire area of the sheet that is exposed at the front of the screen. This can avoid a dark line appearing at the periphery of the screen.

The sheet 11 could be mounted to the frame structure 12 in another way. For example, the mounting blocks could be bolted to the external surface of the frame structure. However, it is preferred that the mounting blocks are mounted to the frame structure such that they are inboard of the periphery of the frame structure when viewed perpendicular to the major plane of the installed sheet. A consequence of that can be that multiple frames of this type can be arranged adjacent to each other with substantially no dark line at the interface between them. This can result in a substantially seamless appearance to a composite back-lit screen or wall formed of multiple individual framed screens.

As shown in figure 4, the frame of the screen may be formed from multiple (in this case four) linear rigid elements of frame structure 12. The forward-most pads (15) of the frame support the sheet 11 as it extends across the opening.

Figures 5 and 6 illustrate other examples of how the sheet 11 may be attached to the frame structure. In the example of figure 5 the sheet is attached by bolts 20 which pass through eyes in the sheet into threaded holes in the frame structure 12. In figure 6 the sheet is attached by self-gripping spring clips 23 on the rear surface of the frame structure. In each case, the forward tip 15 of the frame structure is located so that it is coincident with the periphery 21 of the frame structure when viewed perpendicular to the major plane 22 of the sheet. This means that substantially the entirety of the sheet that forms the forward surface of the screen can be illuminated from behind the sheet.

Any suitable number of illuminators may be provided behind the sheet. Conveniently, the sheet is arranged to be illuminated with a uniform light flux, so that it appears to have the same brightness at all points across its forward face. To achieve this, it may be advantageous to mount one or more illuminators on the interior face 14 of the frame and/or to provide one or more illuminators that selectively illuminate the periphery of the forward face of the sheet. In one example, a row of lamps may be provided along the length of each side of the frame. Where multiple illuminators are provided, there may be a control system, such as one or more dimmers, arranged for altering their relative intensity so as to balance the optical flux across the forward face of the screen.

The interior face of the frame structure may be tinted to adjust its reflectivity. For example it may be painted black, white or grey. This may help to make the light distribution even at the periphery of the sheet.

The or each illuminator may, for example, be an LED illuminator. It may have a constant emission colour or its emission colour may be variable. The or each illuminator may comprise multiple sub-illuminators (e.g. red, green and blue LEDs) which can be controlled in combination to yield a desired emission colour.

Figure 7 shows a composite screen comprising multiple individual screens 30-33 disposed side-by-side in an array. Figure 7 shows the composite screen as viewed from the front. Each individual screen is provided with respective illuminators 34 for shining through the translucent sheet of that screen. A controller 35 is arranged for controlling the illuminators. The controller 35 is responsive to an input 36 for programming the controller 35 to use a certain illumination sequence or to command the controller in real time, e.g., from a lighting control desk. The controller can control the intensity of the back-lighting of each individual screen independently of the others. The controller can also control the colour of the back-lighting of each individual screen independently of the others. This set-up can provide advantages when the composite screen is being used to illuminate a filming set. The illumination provided by the screen can be adapted to simulate light in a setting that is being replicated on the filming set. For example, if on the filming set a cloud is supposed to have passed across the sun, the intensity of back-lighting of one or more upper ones of the individual screens can be reduced. Or if on the filming set a campfire is being simulated, the intensity of one or more lower ones of the individual screens can be increased and their illumination can be made to flicker yellow and red. A system of this type can also be used to provide a background of a constant colour for chroma key filming.

The screen can be lit from behind. In one arrangement, the lighting of the screen from behind may be uniform. That may allow chroma keying to be performed anywhere over the screen. However, if the colour chosen for chroma keying is an obtrusive colour, this may result in light from parts of the screen that are to the side of a subject such as an actor illuminating the sides of the subject. Illuminations and reflections of the chroma keying colour can cause a glow around the sides of the subject in the chroma keying colour. This interferes with the distinction between the subject and the background which gets keyed out in processing. This results in the edges of the subject being misinterpreted as background and disappearing in processing, as a computer cannot distinguish between the background and the coloured glow around the subject. This effect is called green spill, as green is the most commonly used background in chroma keying. One approach to reduce the effects of green spill, and to provide other affects, is for the screen to be illuminated non-uniformly. Some options for this will now be discussed.

In a first arrangement, a redirectable illuminator is located behind the screen. It may, for example be one or more lumieres on one or more pan/tilt heads. The direction of each lumiere may be controlled manually or by motors. One or more such lumieres are arranged to play onto the rear of the subject talent/object so as to illuminate a region that -from the view of a camera -extends peripherally around the profile of the subject. Regions of the screen further from the subject may be not illuminated from the rear, or may be illuminated with less intensity and/or in a different colour from that with which the peripheral region around the subject is illuminated. The peripheral region may, for example extend less than 5 degrees, less than 10 degrees or less than 30 degrees from the profile of the subject as viewed by the camera. This can result in a reduced level of side-illumination of the subject. Instead of one or more redirectable lumineres, multiple lumieres arranged to illuminate in fixed directions may be turned on and off at appropriate times to provide a similar effect. Different lumieres may illuminate the subject as it moves around in front of the screen so that the glow (or reflections/illumination) of the chroma keyed colour on the edges of the subject is reduced equally regardless of where the subject stands. The colour of the light which illuminates the periphery of the subject may be the same colour as the digital post-processed background. This makes it easier for the edges of the subject to be integrated into the later background and produces a more natural processed image.

Instead of a backlit screen, the screen could be an illuminating wall. That is a wall that comprises a planar array of illuminators such as LEDs. The illuminators of the wall may be selectively turned on or off to illuminate only a peripheral region around a subject of the type described above.

In more detail, there may be a wall provided with internal illuminators in the plane of the wall. It may, for example be an LED wall comprising a matrix of LEDs. Such walls are known for displaying an image behind a subject. This approach may be used to reduce the need for post-processing. When a wall of this general type is used for rear or side illumination of a subject, some factors may be noted.

1. The rear or side illumination need not be at high resolution. Instead of a pixel pitch of approximately 1mm, which may be chosen for an LED wall, a large pixel pitch may be selected in the present application. For example, the pixel pitch may be 5mm or higher, lOmm or higher or 20mm or higher. This can reduce the cost of the screen.

2. The region that is illuminated may be selected to be (a) just behind and in the periphery of a subject, as viewed from a camera (for, e.g., chroma keying) or (b) to the side of a subject and optionally outside the frustum of a camera (so as to apply an illumination effect to the subject). The rest of the screen outside of these regions may be the colour of the later digitally processed background so as to reduce the amount of the screen in the chroma keyed colour.

3. When only a region behind and in the periphery of a subject is being illuminated, that region may be selected, and the display wall controlled, automatically or manually. For automatic control, a controller may analyse the output of the camera, and determine where in the image illumination from the wall is not detected. That region may be taken to represent a region of the field of view that is occupied by the subject. Then the controller may control the wall so that only that occupied region and its periphery are illuminated. The outer boundary of the periphery may be, for example, 30cm or less or 1m or less from the occupied region. The occupied region may change from time to time as an actor moves. The controller may repeatedly detect the occupied region and control the wall accordingly. Difference keying may be used to detect where in an image captured by the camera the subject is.

4. A diffuser such as a roughened sheet of glass or polymer or a gauze sheet may be disposed in front of the screen. This can help to disguise the edges between individual pixels of the screen, which may be especially useful when the LED wall is of relatively low resolution.

In a second arrangement, one or more illuminators located so as to illuminate the rear of the screen may be used to provide illumination effects. For example, one or more illuminators illuminating a subset of the area of the screen may be configured to illuminate the rear of the screen with red or yellow light so as to give the impression of a fire illuminating the rear and/or side of a subject.

Figure 8 shows the interface between two individual screens of the type discussed above. The tips 15 of the screens can be located adjacent to each other. This can result in there being substantially no dark line at the interface between the adjoining screens. The major planes of the adjoining screens may be coincident, as in the example of figure 7, or angled with respect to each other, as in the example of figure 8. This can allow non-planar back-lit screens with a substantial absence of shadow lines to be created. The mutually angled screens may, for example, form a two-or three-sided bay in front of which a performer can be located.

The frame structure 12 may be formed in any convenient way. For example, it may be formed of aluminium extrusion. The frame structure may have a constant cross-sectional shape along its length.

The sheet may be flexible or rigid. It may, for example be a fabric or polymer sheet or a ground or etched glass sheet.

The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

CLAIMS1. A back-lit screen comprising: a rigid frame extending around the periphery of the screen and having a front face, the front face having an interior face which defines an opening, and an outer face which defines the exterior contour of the frame transversely to the opening; and a translucent sheet extending across the opening; the frame being configured so that over at least a part of the periphery of the screen the forward-most part of the interior face is coincident with the exterior contour of the frame.
2 A back-lit screen as claimed in claim 1, wherein the translucent sheet bears on the forward-most part of the frame to extend across the opening.
3. A back-lit screen as claimed in claim 1 or 2, wherein the translucent sheet is flexible and is secured to the frame in a recess on the outer face of the frame.
4. A back-lit screen as claimed in any preceding claim, wherein the frame comprises a plurality of linear elements joined together to define the opening.
5. A back-lit screen as claimed in any preceding claim, comprising an illuminator located behind the sheet for shining light through the sheet.
6. A back-lit screen as claimed in claim 5, wherein the illuminator is carried by the frame.
7. A back-lit screen as claimed in claim 5 or 6, wherein the illuminator is elongate and extends along at least a part of the frame for preferentially illuminating a peripheral portion of the sheet.
8. A back-lit screen as claimed in any of claims 5 to 7, wherein the illuminator is controllable to vary the colour of light emitted therefrom.
9. A composite back-lit screen comprising a plurality of individual back-lit screens as claimed in any of claims 1 to 8 located adjacent to each other.
10. A composite back-lit screen as claimed in claim 9, wherein the individual back-lit screens are located adjacent to each other such that a forward-most part of one of the screens is located adjacent a forward-most part of another of the screens.
11. A composite back-lit screen as claimed in claim 9 or 10, wherein the individual back-lit screens are located adjacent to each other such that their respective translucent sheets are coplanar.
12. A composite back-lit screen as claimed in any of claims 9 to 11, further comprising a controller for independently controlling the colour and/or intensity of illuminators located to shine light through respective ones of the individual screens.