AU648931B2

AU648931B2 - Videophone terminal

Info

Publication number: AU648931B2
Application number: AU22156/92A
Authority: AU
Inventors: Gunter Kohler; Hans Reiber
Original assignee: Alcatel NV
Current assignee: Alcatel Lucent NV
Priority date: 1991-09-10
Filing date: 1992-09-07
Publication date: 1994-05-05
Anticipated expiration: 2012-09-07
Also published as: DE4129963A1; NZ244249A; EP0532928A1; AU2215692A

Description

P/00/011 28/5/91 Regulation 3.2 6 8931

AUSTRALIA

Patents Act 1990 s e

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: "VIDEOPHONE TERMINAL" The following statement is a full description of this invention, including the best method of performing it known to us:- 2 This invention relates to an arrangement for video communication incorporating a projection screen.

A prioi arrangement is known from DE 34 31 902 Al. It comprises a video camera and a video display device, e.g. a picture tube, where its optical axes are concentrated by mirrors, with reference to a viewer. This is achieved by positioning in the device a semi- or partiaiiy transmitting mirror, between the video camera and the viewer, for deflecting the beams coming from the picture tube in the direction of the viewer, so that from there on, the beam path coincides with that of the video camera. The latter receives the beams coming from the direction of the viewer, as far as they penetrate the partially transmitting mirror. Depending on the type of arrangement, this one mirror may be sufficient, provided that the video camera and picture tube are installed in the device so that their optical axes are vertical to each other. If this is not the case, a second reflecting mirror is necessary which reflects the beams of the picture tube to the partially transmitting mirror.

S.The task on which the invention is based was to create a price effective arrangement of the type described in the introduction, with a particularly large image with a diagonal of approx. 1 meter and high image resolution.

2 This specification describes an arrangement for video communication, comprising a video camera, a video display device, and a partially transmitting mirror positioned in the beam path between the video camera and a viewer for deflecting the beams coming from the video display device such that their direction coincides with that of the beam path between the video camera and the viewer, wherein between the video display S device and the partially transmitting mirror, a ground-glass screen is provided on which 25 a real image is formed by projection.

The given solution has the advantage that a device with a large image can be produced at relatively low cost. By comparison, a picture tube with a diagonal of 1 meter would be considerably more expensive. Furthermore, an ergonomically unsound, large design depth and greater total weight would result, as high-resolution picture tubes can only be implemented with shallow deflection angles.

The invention is described by means of practical examples which are shown in theaccompanying drawings wherein: Figure 1 is an arrangement for video communication in a desk with integrated mirrors, a video camera, and a video display device with three monochrome projection tubes, in perspective view; Figure 2 another implementation of the arrangement, in desk-top form, in schematic side view; Figure 3 a further implementation of the arrangement, in upright form, in schematic side view; Figure 4 another implementation of thearrangement implemented in upright form, in schematic side-view.

The implementations of the arrangements for video communication as shown in the figures are all so-called multi-media terminals with large screens on the video display devices and high image resolution, i.e. the display has a diagonal of e.g. one meter length and an image dot density of 1200 x 1600 pixels or more. The principle described in DE 34 31 902 Al for beam control of video camera, video display device S or picture tube and partially transmitting mirror is retained, however, a ground glass screen is included between picture tube and mirror, to create a projected, real image and picture enlargement is achieved with an optical system and, if necessary, with at 15 least one further deflection mirror positioned in the beam path of the picture tube. The colour picture is projected onto the ground-glass screen by three small monochromatic projection tubes, provided with red, green and blue phosphors, via three optical lens systems and one or more deflection mirrors with an enlargement factor of approx. 1:10.

Instead of three optical sysi)., is, an integrated optical system comprising an optical combiner (consisting of prisms or mirrors) can be used to combine the three part images. The use of a single colour picture projection tube and a single optical system is also possible. The parallax-free video communication is made possible by the video camera positioned behind the partially transmitting mirror.

With the implementation as shown in Figure 1, the arrangement is housed in a desk 25 The colour picture is projected onto a mirror by the three monochrome projection tubes (R1, R2, R3) arranged side by side and associated optical lens systems (01, 02, 03), the optical axes (Al, A2, A3) of the picture tubes are directed to the centre of the mirror. There, the three beam paths are deflected to the vertical and combined onto a ground-glass screen which is installed in, or under the desk-top surface From there, the beam path is directed to another partially transmitting mirror (HS) from where it is finally reflected to the viewer Behind this mirror (HS) the video caniera is installed in such a way that its optical axis is directed through the mirror (HS) onto the viewer Its beam path coincides with the beam path of the picture tube reflected by the mirror The mirror (HS) is partially transmitting at least in the area of the video camera lens.

The desk-top is of a rectangular or cuboid shape and, utilising its length, the optical equipment is installed so that the projection tubes (R1 to R3) are installed close to one end and the mirror close to the other end. The second mirror (HS) can be installed as a rigid mirror or on the inner side of a hinged lid With the implementation as shown in Figure 1, the lid is hinged at at the rear longitudinal edge of the desk the viewer sits in front of the front longitudinal side. The mirror surfaces are arranged with a 900 rotation around their vertical axis.

The implementation according to Figure 2, differs from the previous version in that the lid with the mirror (HS) and the video camera is linked by a joint to the desk at one transverse side. The viewer then sits at the opposite transverse side.

Furthermore, the projection tube(s) is/are arranged underneath the mirror which deflects the beam path to the vertical. The optical axis/axes of the projection tube(s) is/are directed towards the viewer side. There, a further mirror which reflects the beam path to the mirror is inserted in the desk.

Figure 3 shows a version designed as an upright unit, where the ground-glass screen is installed at approximately half its height and very nearly horizontally, whilst the mirror is slightly tilted and is positioned just above ground level. The partially transmitting mirror (HS) is installed at an angle in the upper part of the upright unit The picture which appears on the ground-glass screen is reflected to the outside to S• the viewer by the mirror through a window in the upright unit.

The video camera and the projection tube are installed in the cavity behind the partially transmitting mirror The video camera is installed so that its optical V axis A is directed to the viewer. After penetration of the partially transmitting mirror 25 it coincides with the beam path of projection tube reflected by this mirror to the viewer The projection tube is installed at a downwards tilt. As the space available does not permit a direct alignment of its optical axis onto the mirror on the bottom of the upright unit, anot.her deflection mirror (S1) is attached to the rear wall of the upright unit which reflects the beams onto it.

Figure 4 shows another version of an arrangement with an upright unit which has been designed in a similar way to the one previously described. The video camera is again positioned behind the partially transmitting mirror so that its optical axis is directed through this mirror onto a viewer and that it coincides with the beam path of projection tube reflected by the mirror In this version, the projection tube is mounted next to the mirror close to the housing base, so that its optical axis is directed upwards. There, a deflection mirror (S1) is mounted underneath the video camera which reflects the beams to the mirror from where they are deflected to the gr0und-glass screen and the partially transmitting mirror

(HS).

Beside the mirror close to the base, a commercially available, monochromatic CCD camera is mounted, which is directed onto the ground-glass screen and is used for automatic convergence adjustment. The camera represents a picture sensor, whose signals are transferred to a digital signal processor via an A/D converter for convergence control. Such an arrangement is described in DE 39 20 965 Al.

To achieve particularly intense, visually perceived picture brightness and contrasts, a lenticular screen can be used instead of the ground-glass screen Such a screen converges the light so that it appears particularly bright when the virtual image is observed vertical to the centre. The perceived brightness however drops, the more the S angle of observance deviates from the vertical. A decreasing picture brightness 15 towards the sides or edges of the picture is also caused by the projection tubes. To compensate these disadvantages, it is suggested to make the partially transmitting mirror (HS) partially transrmitting only in the area of the beam path of the video camera and (light) transmission decrease towards the edges. The reflection factor then "T.i increases towards the edge and with it the brightness.

Claims

1. A arrangement for video communication, comprising a video camera, a video display device, and a partially transmitting mirror positioned in the beam path between the video camera and a viewer for deflecting the beams coming from the video display device such that their direction coincides with that of the beam path between the video camera and the viewer, wherein between the video display device and the partially transmitting mirror, a ground-glass screen is provided on which a real image is formed by projection.

2. An arrangement as claimed in claim 1, wherein the video display device consists of three monochrome projection tubes arranged side by side and provided with red, green, and blue phosphors, respectively, and associated optical lens systems.

3. An arrangement as claimed in claim 1, wherein the video display device is ooo formed by an integrated optical system comprising an optical combiner. :i

4. An arrangement as claimed in claim 1, wherein a lenticular screen replaces the S 15 ground-glass screen.

An arrangement as claimed in any one of the preceding claims, wherein the partially transmitting mirror is partially transmitting only in the area of the beam path of the video camera and that the transmission decreases toward the edge of the mirror.

6. An arrangement as claimed in any one of the preceding claims, wherein at least one reflecting mirror is positioned in the beam path between the video display device and the ground-glass screen for deflecting the beams.

7. A video communication arrangement substantially as herein described with reference to the accompanying drawings. V 25 DATED THIS THIRD DAY OF SEPTEMBER 1992 ALCATEL N.V. ABSTRACT The arrangement consist of a video camera a video display device a partially transmitting mirror a ground-glass screen and, depending upon the version, at least one reflecting mirror The beams emitted from the projection tube are reflected by the mirror onto the partially transmitting mirror (HS) which deflects them to a viewer Between the mirror (HS) and the viewer the optical axis (A) of the beams from the projection tube is in register with that of the video camera (V) mounted behind the mirror The ground-glass screen is arranged in the beam path of the projection tube in front of the partially transmitting mirror The arrangement can be installed either in a desk or an upright unit A large picture with high image resolution can be achieved with this arrangement. FIGURE 3. *l ft i a a *e*