Abstract: A virtual TV set combines actors and objects with computer-generated virtual environments
in real time. Nowadays, this technology is widely used in television broadcasts and cinema
productions. A virtual TV set consists of three main elements: the stage, the computer-system and the
chroma-keyer. The stage is composed by a monochrome cyclorama (the background) in front of which
actors and objects are located (the foreground). The computer-system generates the virtual elements
that will form the virtual environment. The chroma-keyer combines the elements in the foreground
with the computer-generated environments by erasing the monochrome background and insetting
the synthetic elements using the chroma-keying technique. In order to ease the background removal,
the cyclorama illumination must be diffuse and homogeneous, avoiding the hue differences that are
introduced by shadows, shines and over-lighted areas. The analysis of this illumination is usually
performed manually by an expert using a photometer which makes the process slow, tedious and
dependent on the experience of the operator. In this paper, a new calibration process to check and
improve the homogeneity of a cyclorama’s illumination by non-experts using a custom software
which provides both visual information and statistical data, is presented. This calibration process
segments a cyclorama image in regions with similar luminance and calculates the centroid of each of
them. The statistical study of the variation in the size of the regions and the position of the centroids
are the key tools used to determine the homogeneity of the cyclorama lighting.
Keywords: chroma-keying, cyclorama, illumination, virtual TV set, mixed reality