Simple, Accurate, and Robust Projector-Camera Calibration
Daniel Moreno and Gabriel Taubin
School of Engineering
Brown University
Providence, RI, USA
Email: {daniel moreno,gabriel taubin}@brown.edu
Abstract—Structured-light systems are simple and effective
tools to acquire 3D models. Built with off-the-shelf components,
a data projector and a camera, they are easy to deploy and
compare in precision with expensive laser scanners. But such
a high precision is only possible if camera and projector are
both accurately calibrated. Robust calibration methods are well
established for cameras but, while cameras and projectors can
both be described with the same mathematical model, it is not
clear how to adapt these methods to projectors. In consequence,
many of the proposed projector calibration techniques make
use of a simplified model, neglecting lens distortion, resulting
in loss of precision. In this paper, we present a novel method
to estimate the image coordinates of 3D points in the projector
image plane. The method relies on an uncalibrated camera and
makes use of local homographies to reach sub-pixel precision.
As a result, any camera model can be used to describe the
projector, including the extended pinhole model with radial
and tangential distortion coefficients, or even those with more
complex lens distortion models.
Keywords-structured-light; camera; projector; calibration;
local homography;
I. INTRODUCTION
Structured-light systems are the preferred choice for do-it-
yourself 3D scanning applications. They are easy to deploy,
only an off-the-shelf data projector and camera are required,
and they are very accurate when implemented carefully. A
projector-camera pair works as a stereo system, with the
advantage that a properly chosen projected pattern simplifies
the task of finding point correspondences. In such systems,
projectors are modeled as inverse cameras and all consid-
erations known for passive stereo systems may be applied
with almost no change. However, the calibration procedure
must be adapted to the fact that projectors cannot directly
measure the pixel coordinates of 3D points projected onto
the projector image plane as cameras do.
Viewpoint, zoom, focus, and other parameters ought to be
adjusted, both in projector and camera, to match each target
object size and scanning distance; invalidating any previous
calibration. Therefore, structured-light systems must be cali-
brated before each use in order to guaranteed the best result,
turning the calibration procedure simplicity as valuable as
its precision. In this paper, we present a new calibration
procedure for structured-light systems that is both very easy
to perform and highly accurate.
Figure 1. Structured-light system calibration
The key idea of our method is to estimate the coordinates
of the calibration points in the projector image plane using
local homographies. First, a dense set of correspondences
between projector and camera pixels is found by projecting
onto the calibration object identical pattern sequence as the
one later projected to scan the target, reusing most of the
software components written for the scanning application.
Second, the set of correspondences is used to compute a
group of local homographies that allow to find the projection
of any of the points in the calibration object onto the
projector image plane with sub-pixel precision. In the end,
the data projector is calibrated as a normal camera.
Our main contribution is a method for finding correspon-
dences between projector pixels and 3D world points. Once
those correspondences are known any calibration technique
available for passive stereo can be applied directly to the
structured-light system. Our method does not rely on the
camera calibration parameters to find the set of correspon-
dences. As a result, the projector calibration is not affected
in any way by the accuracy of the camera calibration.
We show, as a second contribution, that the proposed
calibration method can be implemented in such a way that no
user intervention is necessary after data acquisition, making
the procedure effective even for unexperienced users. To