Subpixel Image Registration Using Circular Fiducials

Abstract

The design of fiducials for precise image registration is of major practical importance in computer vision, especially in automatic inspection applications. We analyze the subpixel registration accuracy that can, and cannot, be achieved by some rotation-invariant fiducials, and present and analyze efficient algorithms for the registration procedure. We rely on some old and new results from lattice geometry and number theory and efficient computational-geometric methods.

A phantom based laser marking workflow to visually assess geometric image distortion in magnetic resonance guided radiotherapy

“…Future work will be dedicated to building a phantom with larger and exactly spherical fiducials from MR-visible silicone, to profit from the achievable subpixel resolution for its center determination [10] in MR reconstructions. It is advisable to print 2D spherical coordinate on the fiducials to ease reading of laser mark positions with their rectilinear coordinates.…”

“…Using enlarged and interpolated fiducial visualization ( Fig. 1 d)) allowed to profit from subpixel resolution for the determination of its center position in the DICOM patient coordinate system, which under ideal conditions can be as low as 10% of pixel size for spherical fiducials [10] . Its reconstructed sagittal and coronal MR coordinates were sent to the horizontal and the vertical laser modules of the laser bridge, while its transversal coordinate was used to move the MR scanner’s patient table, thereby bringing the respective fiducial into the crossing point of all movable lasers.…”

Reliable Fiducial Detection in Natural Scenes

“…The many proposed fiducial designs include: active LEDs [3,4]; black and white concentric circles [5]; coloured concentric circles [6,7], one-dimensional line patterns [8]; squares containing either two-dimensional bar codes [9], more general characters [10] or a Discrete Cosine Transform [11]; and circular ring-codes [12,13]. The accuracy of using circular fiducials is discussed in [14]. Three dimensional fiducials whose images directly encode the pose of the viewer have been propsed by [15].…”