WO2002031594A1 - 3d retroreflective screen - Google Patents

Abstract

A retroreflective backdrop screen comprising a screen provided with reference markings, such as reference points, grid lines or a chequerboard pattern, having a different degree of reflectivity than the background reflectivity of the backdrop.

Description

3D Retroreflective Screen

This invention relates to retroreflective screens, more particularly, though not exclusively, to screens adapted to form backdrops in virtual studio arrangements in which an background image is superimposed on an image effected by illumination projected on to a backdrop screen against which foreground objects and actors, for example, can be imaged.

The conventional approach to this has been to illuminate the backdrop with a particular colour, usually blue, which can be distinguished by software associated with a video imaging system so as to remove it from the image, a separate image, as of a background scene, or a virtual studio, being played in all parts of the image except the foreground objects. This is known as "chromakeying".

A recent development has been the substitution of a retroreflective screen for the conventional backdrop screen, illuminated by a light source - which can be a ring of bright light emitting diodes (leds) - situated on the camera axis so as to retroreflect back into the lens. This requires very much less intense illumination, and has other advantages.

In connection with the generation of three dimensional images, conventional chromakeying backdrop screens have been marked with reference points or a grid, which can be picked out by the vision system and used to compute depth information which can be reproduced in an image to give a 3D impression. On a blue backdrop, these reference points or grid lines have been, for example, picked out in a darker blue.

Such a system is described, for example, in WO95/30312. The present invention provides a means of achieving similar three dimensional imaging using a retroreflective backdrop screen.

The invention comprises a retroreflective backdrop screen comprising a screen provided with reference markings having a different degree of retroreflectivity than the background retroreflectivity of the backdrop.

The reference markings may comprise reference points and/or grid lines.

A simple way of achieving this is to overprint a uniformly retroreflective screen with reference points or grid lines of retroreflective ink. The markings may retroreflect to a greater extent than the background. The difference in retroreflectivity may be 50 - 70 grey scale units.

A typical grid size may be 150 mm square, though the grid need not be square. A particular part of the backdrop may be covered by the reference markings, or all of it, as may be required for any particular studio set-up.

Embodiments of retroreflective backdrop screens according to the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a face-on view of one embodiment;

Figure 2 is a cross-section of the embodiment of Figure 1 on the line II - II;

Figure 3 is a face-on view of another embodiment; and

Figure 4 is a face-on view of another embodiment. The drawings illustrate retroreflective backdrop screens 11 provided with reference points 12 (Figures 1 and 2) grid lines 13 (Figure 3), and a chequer-board pattern (Figure 4) of squares 15 having a different degree of retroreflectivity than the background retroreflectivity of the backdrop 11 - that of the areas 14 outside the reference points 12, grid lines 13 and squares 15.

The screens 11 are first coated or printed with retroreflective microheads or with other retroreflective materials such as non-silvered heads backed by metal or mica flakes - these make up the areas 14. They are then overprinted with a retroreflective ink, which has a different and conveniently greater degree of retroreflectivity than the background areas 14. Different degrees of retroreflectivity may be arranged for, by using different concentrations or different sizes of microbeads in an ink or coating. A difference of 50-70 grey scale units on an image is convenient for 3D effects. There need be little or no visible colour or brightness differences off the illumination axis.

The spacing of the grid lines of Figure 3, the reference points 12 of Figure 2 and the squares 15 of Figure 4 may be about 150 mm, which is convenient for current 3D processing, although other spacings are possible and may be desirable in some studio arrangements. Vertical and horizontal spacing may be different.

With some processing arrangements, a random distribution of reference points, giving the screen a speckled appearance under retroreflection, may be used instead of an orderly array.

Claims

1. A retroreflective backdrop screen comprising a screen provided with reference markings having a different degree of retroreflectivity than the background reflectivity of the backdrop.

2. A screen according to claim 1, in which the reference markings comprise reference points.

3. A screen according to claim 1 or claim 2, in which the reference markings comprise grid lines.

4. A screen according to any one of claims 1 to 3, in which the reference markings comprise a chequerboard pattern.

5. A screen according to any one of claims 1 to 4, in which the reference markings are overprinted in retroreflective ink.

6. A screen according to any one of claims 1 to 5, in which the reference markings retroreflect to a greater extent than the background.

7. A screen according to any one of claims 1 to 6, in which the difference in retroreflectivity is 50-70 grey scale units.

8. A screen according to any one of claims to 7, having a grid size 150mm square.

9. A screen according to any one of claims 1 to 8, in which part only of the backdrop is covered by reference markings.