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 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.
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.
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…