Lighttwist

Lightwist is an OpenSource software project for large scale projection of images on surfaces such as a large wall, cylindrical screen, hemispheric dome, or more complex shapes. It is designed to handle from one to a very large number of projectors simultaneously. It is the result of computer vision research in the field of structured light reconstruction, applied to technological arts.

The goal

The most important goal of Lighttwist is to make it easy for artists to project on large scale surfaces, immersive or not, at highest resolution possible while keeping the process affordable. We believe that using multiple projectors is the best way to achieve this and to truly free the artists from the traditional projection constraint of a “square image on a flat surface”.

How it works

Lighttwist features two main parts: scanning and projecting.

The first part handles the scanning of a screen by computing the deformation that must be applied to each projected image in order to obtain a coherent image from the point of view of a camera. This process can handle arbitrary screen geometry as long as a single camera sees the whole screen. The projectors should be positioned to cover the whole screen, with an overlap between adjacent projectors. Gamma and color calibration is also included in the scanning process. It can be argued that when one knows the exact shape of the screen and the exact position and characteristics of the projectors, one can compute this deformation directly. However, Lighttwist makes the process simpler and more general: it uses a camera to look at the screen and figure out automatically all the needed information.

The second part, projecting, can play and mix various media, such as video, images, 3D models, all at the same time, with live mixing, as well as immersive sound spatialization and synchronization (using puredata).

In summary, Lighttwist:

  • focuses on practical use by artists outside the research lab.
  • makes large scale projection less expensive by using multiple projectors instead of a single super hi-res projection.
  • uses a single camera as a virtual projector to avoid having to calibrate the position of the positions.
  • does not require modelling the screen.
  • handles various media types: images, video, 3D, sound.
  • is high performance, interactive.

How to use Lighttwist in practice

  • Figure out the projection setup. Is it 9 projectors on a cylinder? Is it a single projector bouncing on a spherical mirror? 3 projectors on a wall? How many machines and how many projectors per machine?
  • Take a camera and put it where the viewer is intended to be. For a wall, a standard will do; for a cylindrical screen or dome, a camera with fisheye (or catadioptric lens) in needed. Remember that most importantly the camera must see the whole screen. It represents the virtual projector for which content is created.
  • Get Lighttwist to figure out the mapping between the projectors and the camera. Once this is done, any image can be projected so it looks coherent from the point of view of the camera.
  • Prepare some content in the camera image coordinates. It can be video or still images, or even 3D models. In the case of a cylinder, content format is a large rectangle (an unfolded cylinder).
  • Use the player to play and mix the content, either interactively or through playlists.

Lighttwist in real life

Since 2004, Lighttwist has been used in a variety of projects. The largest was with 9 projectors on a cylindrical screen 10 feet high and a diameter of 40 feet. The smallest one was a 3 feet diameter plexiglass cylinder with a single projector and a spherical mirror. A short video presents the software as it was used in some of  those projects.

What’s next

We are now working on a stereo version of Lighttwist. Traditionally, stereo works directly on a single wall in front of the observer, such as an IMAX screen. We are interested in a cylindrical stereo projection. In such a setup, the orientation of the observers inside the cylinder is unknown. We developped a solution that should be demonstrated at LGM 2009 in May. Moreover, a lot of work is being done on capturing stereo-immersive panoramas using cameras.

The software

A user manual was made to describe how to download, install, and use Lighttwist. At this time, it is in french only, but nicely illustrated… :-)

5 thoughts on “Lighttwist

  1. Dear Linux enthusiasts,

    Please see my idea about the Immersive Environment Instrument.
    http://vix.ca/blog/portfolio/vix-current-projects/immersive-environment-instrument-iei/

    I am the artist who will use your code!

    I use Ubuntu on all my pro graphics design.
    However, I have had to use a Mac for my projections – Isadora.

    See my site for info on my upcoming Brooklyn show

    Please subscribe to my list so you can be notified of the URL to watch
    http://eepurl.com/dSjpX
    The stream will be live, so it will occur the same time as the
    concert. Information on my site.

    Warm Regards,

    Victoria Gibson
    Integrated Media Artist, Curator

  2. “Holly Scott”, that looks awesome….

    I’m working with SpeedDreams (an open source car race simulation) to allow it to display nicely on super wide (multi-projector) setups. The game normally displays full screen (across whatever screens you have tiled), and you can split this area down into split screens (‘(‘ and ‘)’ keys) to allow multiple player/views on single PC.

    Although still in development, the SVN version has the ‘Span Split’ option, in which multiple split screens (one for each projector) will be used to display a single view and the image will be compensated for ’tilt in’ of the monitors/projection screen. The ‘bezel compensation’ option allows either for placing a gap between the views (ie. for monitor setup) or cause the views to overlap (ie. for projector setup).

    I’d be _really_ interested if this can work with your code, hopefully this description grabs your interest. I only have 1 projector so would have difficulty testing it…

    Cheers,
    Simon

    PS. The demo video won’t download, seems to have a permissions problem.

  3. Can you please tell me more about the player, or is there information online I missed. I’m looking for a 4Kx4K fulldome playback system with two 4K projectors and two high end workstations driving them, each doing 4Kx2K (approximately) and an edge blended down the middle.

    ps: the avi movie on the Lighttwist web page is missing
    lighttwist_presentation_en.avi

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