After analyzing the differences of vignetting effect between devices as well as the symmetry and influence of the reflectance of the target on the luminance falloff, vignetting filters were calculated.
Finally, vignetting filters were applied to original HDR pictures.
Before the vignetting correction, RMSEs calculated for the seven largest apertures vary between 31.4 percent (f/2.8) and 7.4 percent (f/5.6) for CAM#1FE#1, and between 32.7 percent (f/2.8) and 5.8 percent (f/5.6) for CAM#2FE#2.
The semicircular setup used in this study differs from the ones used in other studies evaluating the vignetting effects of fisheye lenses [Inanici 2006; Jacobs and Wilson 2007].
Targets are of two different reflectance coefficients (gray and white) and make thus possible the evaluation of vignetting effect on the basis of two different gray tones.
In Jacobs and Wilson [2007] the vignetting effect of the fisheye lens was determined without comparing the captured values with the physical luminances in order to avoid absolute photometric calibration.
As the luminances of the targets are not perfectly constant over the angle [theta], it is still necessary to evaluate the vignetting effect by comparing physical luminance measurements with luminances extracted from the HDR picture instead of evaluating the luminance falloff from the center of the image to its border.
In this study, the targets are locally calibrated, according to their reflectance, in order to avoid, in the determination of the vignetting effect, the introduction of errors due to the photometric calibration.
