We present a novel method that allows for simultaneous geometric and radiometric calibration of a projector-camera pair. It is simple and does not require specialized hardware. We prewarp and align a specially designed projection pattern onto a printed pattern of different colorimetric properties. After capturing the patterns in several orientations, we perform geometric calibration by estimating the corner locations of the two patterns in different color channels. We perform radiometric calibration of the projector by using the information contained inside the projected squares. We show that our method performs on par with current approaches that all require separate geometric and radiometric calibration, while being more efficient and user friendly.
Design of calibration patterns
|Printed chart||Projected chart|
The projected pattern is specifically designed to allow for simultaneous geometric and radiometric calibration of the projector. The red pixel intensities (in %) of the squares vary across the chart. Example intensities are shown in the top-right corner. The printed pattern is composed of a conventional yellow-white checkerboard of identical dimensions to that projected. With this choice of colorants, we are able to isolate the two patterns in different color channels in the captured images.
We capture 2 images per calibration board orientation and perform geometric and radiometric calibration at the same time, whereas other methods [2,3,4,5,6,7] perform only geometric calibration. This results in ample time savings.
|(a) Non-gamma compensated
RMSE = 0.331 mm
|(b) Ground truth method*
RMSE = 0.056 mm
|(c) Our method
RMSE = 0.055 mm
We perform a planarity test to validate the performance of the radiometric calibration in a real world scenario. The test consists of fitting a plane into a point cloud and estimating their fit. We therefore reconstruct a flat board by using a phase-shifting SL code. We perform three reconstructions of the flat surface, of size 10 x 10 cm, by projecting: (a) linear patterns, gamma compensated patterns with (b) gamma computed using a ground truth method*, and (c) gamma computed using our proposed method. Our method is vastly superior to (a), thus confirming the need for radiometric calibration. It is also faster and more convenient than (b), demonstrating the effectiveness of simultaneous geometric and radiometric calibration.
*11 consecutive projections of grayscale patterns of linearly increasing intensities.
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