Reflective paint for 3D video conference effect

At the hardware store recently I noticed spray cans of White Knight "Reflect-All light reflective paint" and thought it might be suitable for spraying on a walls to make a high efficiency screen for projector. I tried it out in a typical tutorial room at the ANU. To avoid damaging the walls I sprayed the paint onto a piece of transparent plastic and dark blue cardboard and attached these to the wall and projected onto them. I compared this with flat very light blue wall paint, a whiteboard and a projection screen.

The reflective paint worked as expected. However, working as a retro-reflector, the image only reflected a narrow cone of about ten degrees either side of the projector. This makes it impractical to use for a projection screen in a typical classroom.

The paint may still be of use in some difficult applications, such as in very bright lighting conditions, with a very dim projector, or one in a very large auditorium. The paint did not have the problems I was expecting with stray reflections and so there could be a very bright light source beside the screen without washing out the image.

The paint may have other uses. Because the light is reflected back strongly in the direction of the source, a camera at that point will show the subject in silhouette. This can be used to electronically extract the subject from the background. The subject can then be transmitted to a remote location and inserted into a scene. This effect is commonly created against a black background, reflective grey cloth or a specially coloured surface (chroma key). But the reflective paint would have the advantage of being able to be applied to any coloured surface. The wall of a meeting room or classroom could be painted without interfering with normal use of the room.

For educational or video videoconferencing use, a presenter could be videoed live in the room next to a projected presentation. The wall behind the presenter would act as a screen for the projected image seen by those in the room. The wall would also act as a reflector for the video image. The camera recording the presenter would be able to see them, but not the projected image. As a result just the image of the person could be recorded, or transmitted. Their presentation could be digitally inserted into the same video image, or transmitted separately in a separate video stream. This would provide a much higher quality image (and use less bandwidth) than attempting to record the presentation slides with a camera.

Reflective paint for invisible projection screens

At the hardware store recently I noticed spray cans of White Knight "Reflect-All light reflective paint". This is available in a silver metallic colour, but more interestingly also as a clear varnish. This might be suitable for spraying on a walls to make a high efficiency screen for projector, particularly new low power LED projectors. When not in use the screen would be all but invisible and could be painted on a dark colour wall.

The paint has "microbeads" which act as retro-reflectors, showing up brightly in the dark when a light is shone on them. This is similar to the material used in road markings. The difference is that it is available at the retail level and in a clear form, rather than the bright white used for road markings. Also the beads are much finer than those in road markings. The paint when applied looks like a frosted translucent finish with a rough mat texture. If applied in a thin coat to a very dark shiny surface it is noticeable as a milky film. In a thicker coat it looks like ground glass. But on a lighter matt surface, such as typical flat creme wall paint, it is all but invisible.

Having bought a can and tried it out the paint looks promising. It reflects so much more light than conventional paint that it would make a very good projection surface. This would be particularity useful for new LED projectors, which are not as bright as halogen ones. It would allow projectors to be used in much brighter environments and on dark and uneven surfaces.

But there are some limitations. As with any highly reflective screen, any blemishes are highlighted. The paint would need to be applied professionally, preferably by a trained operator with a professional spray gun, not the retail spray cans. The wall would have to be kept clean, as any grease would show up. Also any abrasive cleaner used may mar the surface. The microbeads reflect light back in a narrow cone, so there is not a wide viewing angle for the screen and the projector has to be near the viewer. The paint could not be used in a room with a brightly lit window, or spotlight opposite, as the reflective surface will show up (but then if used for protection there should not be a window or light opposite anyway).

The material could allow projection in rooms which are usually unsuitable. As an example, the projection surface could have lights or windows on each side. The ambient light would not be reflected towards the viewer, but the image from the projector would be.

Applied to a black or very dark wall this material might provide a way to produce a low cost hologram-like effect for video conferences. There are some systems using half silvered mirrors or film to give the appearance of the person in the room, however these are cumbersome and inflexible. Instead the lighting in the room could be carefully arranged so that it does not reflect from the wall into the camera lens. As a result the wall would be a very dark black, allowing anyone or anything in front to stand out clearly from the background for a very clear video image of the person. An image could be projected onto the same background which would show in sharp relief. With this arrangement two people could be in separate remote locations, with their images projected next to each of them, so they both appear to be standing next to each other at both locations.

It might also be interesting to apply the paint to glass or clear plastic sheeting. This would create a sheet of translucent frosted material which would act as a very good projection surface. A meeting room could have a frosted glass wall onto a corridor, which could be used as the projection screen. With the lighting carefully arranged, the image would be clearly visible in the room, but not in the corridor on the other side.

Before using the material on a large scale in a confined space the safety of the microbeads and the paint they are embedded in would need to be considered. The spray gives off a strong paint smell and some of the microbeads may become airborne in the process.

ps: The pain might also create a new form of subtle graffiti: The reflective paint is not visible during the day, but would show up clearly in car headlights at night.

DimDim Web Conference for E-learning

DimDim is a web conferencing product popular for education. This is because it offers a free service for conferences with up to 20 participants. It also claims to require no software download and be open source. However, it uses Adobe Flash for the audio and video, so that needs to already be installed on the computer used. I found DimDim very easy to sign up for and start a conference with. It has the usual whiteboard, desktop and presentation sharing features of such products. One interesting feature is web co-browsing, where the presenter selects a web page and it is displayed on the participants screens, scrolling synchronised with the presenter's screen.

Co-browsing works very well with HTML Slidy presentations, such as my "Learning to lower costs and carbon emissions with ICT" (slides). This could be very useful for bandwidth efficient presentations, as the Slidy slides use a lot less storage than the typical Powerpoint or OpenOffice.Org presentation. With the video frame rate turned down (or off) and the audio reduced to telephone quality, the web conference would use very little bandwidth. USQ's ICE open source e-learning content creation system produces Slidy as part of a course package, which would then work well with DimDim.

One catch is that, for security reasons, DimDim does not work with web sites which require you to enter a user-id and password. I found that this stopped access to Moodle courses, even those which allow access without a user id (I will ask DimDim to fix this). Another limitation is that the web browsing is not recorded along with the audio, video and other content.