APPLICATION OF PRACTICAL BLACKBODY TECHNIQUE TO DIGITAL PHOTOGRAPHY VISIOMETER SYSTEM

In Digital Photography Visiometer System (DPVS), the uncertainty, caused by the difficulty in real time measurement of the inherent brightness of targets, can be reduced even eliminated by using practical blackbody technique.The visibility measurement error caused by non-blackbody target is analyzed.It is shown that the relative measurement error increases along with the increase of the visibility and the target's reflectivity.To ensure the measurement precision, the target with reflectivity low enough is required.The relations between the near-axis hemispherical-directional reflectivity and the feature parameters of practical blackbody with cuboid st ructure are calculated using multi-reflect method.Without observing the inner side of the practical blackbody, the axial reflectivity is maximum, and the reflectivity decreases as the angle that departs from axis increases.The axial reflectivity sharply deceases as the ratio of body length to aperture side length increases, while the change caused by increase of body width is not obvious.Additionally, in consideration of dispersion imaging, the equation used to compute the blackbody's minimum aperture size required is presented.These results provide the criteria for selecting parameters of practical blackbody in DPVS.Finally, the comparison results of visibilities calculated from observing a blackbody and from a non-blackbody target are show n, and they sufficiently indicate that it is necessary and feasible to adopt the practical blackbody technique in DPVS.