Passive calibration board for alignment of VIS-NIR, SWIR and LWIR images

Infrared Camera Geometric Calibration: A Review and a Precise Thermal Radiation Checkerboard Target

“…Some studies involved the use of a paper-printed checkerboard pattern, along with aluminum foil tape placed on white squares, to provide a greater difference in emissivity and a higher contrast thermal image [ 33 , 34 ]. A few studies implemented the printed checkerboard technique, but not on paper; instead, laser-printed black ink squares on a thin aluminum sheet was implemented [ 35 ], or digitally printed thick black ink squares on a thin sandblasted aluminum plate exposed to a halogen lamp or sunlight for heating [ 25 ]. A recent study proposed the printing of the checkerboard pattern on a Dibond ® panel, an aluminum composite material, but the printing was made using a flatbed ultraviolet (UV) industrial advertisements printer, and heated using an electric fan heater [ 6 ].…”

“…There are two main sources of error that affect the geometrical calibration of visible and IR cameras, namely the efficacy of the calibration target [ 54 ] and the ambiguity in detecting the control points of the images [ 55 ]. These issues tend to magnify when dealing with thermal cameras, as thermal images are typically of lower contrast and modest in quality than visible images [ 25 ]. With radial and tangential lens distortions affecting the images, imprecise calibration results in further errors that affect the certainty of the geometric calibration study [ 56 , 57 ].…”

“…With radial and tangential lens distortions affecting the images, imprecise calibration results in further errors that affect the certainty of the geometric calibration study [ 56 , 57 ]. While few studies described the detailed construction of the used geometric calibration targets [ 6 , 19 , 25 , 37 , 47 , 49 , 51 ], several studies shared little to no details on how the calibration rigs were constructed. Furthermore, many studies involved the manual construction of the targets, such as the manually cut square grids [ 31 ] or the manual aluminum foil and tape placements on the targets [ 19 , 33 , 34 , 36 , 38 ].…”

“…Thus, directly employing the typical paper-printed checkerboard pattern used to calibrate visible cameras to IR cameras is not suitable, as the features of the checkerboard pattern are invisible at normal temperature conditions [ 24 ]. This causes the contrast produced by this pattern in thermal images to appear poor or dim [ 25 ]. Therefore, through varying materials, surface emissivity and thermal conductivities, calibration targets will have distinctive features in the IR spectrum, allowing for the geometric calibration of IR cameras [ 26 ].…”

Real-time multispectral video panorama construction

“…Photogrammetric calibration of DPS cameras is the most universal approach for combining images in the far zone, but requires the use of a test pattern that have high contrast simultaneously in several spectral ranges. Examples of such patterns with typical "chessboard" image are considered in [10]. The results of the calibration allow us to evaluate the matrix of internal and external parameters of the multispectral DPS cameras.…”