Visualizing Concert Hall Reverberation
Spherical Panorama of the Dekelbaum Theater: As discussed before the
spherical array provides a spherical image of the intensities of planewaves from
all directions. We needed to compute a similar visual spherical image of the
space being measured. To do this, we took a regular digital camera, which we
calibrated using standard computer vision procedures. Using this camera we took
several overlapping pictures of the theater from near the locations where audio
measurements were to be made. While the procedures for creating a panoramic
mosaic are well described in the computer vision literature, we simply used a
free version of ptGui, a panoramic toolbox gui available at http://www.ptgui.com/.
It finds correspondences in the images automatically and stitches them into
aomnidirectional spherical image.
Joint Audio-Visual processing and Calibration: In [1] we provide a detailed
outline of how to use cameras and spherical arrays together and determine the
geometric locations of a source. The key observation was that the intensity
image at different frequencies created via beamforming using a spherical array
could be treated as a central projection (CP) camera, since the intensity at
each "pixel" is associated with a ray (or its spherical harmonic reconstruction
to a certain order). When two CP cameras observe a scene, they share an "epipolar
geometry". Given two cameras and several correspondences, it is possible to take
points in one cameras coordinate system and relate them to directly to pixels in
the second cameras coordinate system. Given a single spherical panoramic image
and a corresponding audio panorama image, the transfer can be accomplished if we
assume that the world is on the surface of a far sphere. Further cameras can
make this transfer without this assumption, but we did not pursue this here.
Below are a few links to a program that lets you interact with the images. The program requires
the latest version of MATLAB to run( MATLAB Version 7.3.0.267 (R2006b). If
you do not have the latest version of MATLAB you will need to install the Matlab
component runtime library. To request a copy of this installer please send
an email to AdamOD@gmail.com
The original version does not display well on lower resolution screens so I have included several version for different resoluton
Download Visualization Application Screen Resolution 1280x1024
Download Visualization Application Screen Resolution 1024x768 : this version works well for most laptops