earticle

영어

To test the effectiveness of flash intensity in digital close-range photogrammetry, test methods for the light intensity adjustment of a ring-flash on close-range photographic imaging quality and measuring precision were researched respectively. First, according to the efficiency of the flash, the imaging characteristics, and the gray distribution of the mark points of the image, the identified method of the image gray value for subjective visual analysis was presented, and a quality standard for the close-range photographic image was provided. Then, as a precondition to obtaining the best image quality, based on the estimation theory governing measurement adjustment precision, the changes in measuring precision under conditions of different light intensity and different photographic distances were analysed, and the relationships between measurement precision and light intensity, or photographic distance, were obtained. Finally, the globally optimal imaging quality and measurement precision for any given light intensity were quantified. Experimental results indicated that the root mean square (RMS) errors of the measurement adjustment precision were 0.028 mm, 0.039 mm, and 0.085 mm: the RMS errors in the measuring precision and the corresponding coordinate repeatability were 0.038 mm, 0.053 mm, and 0.118 mm. The best imaging quality was achieved at photographic distances of 3 m, 5 m, and 7 m, with corresponding output light intensities of 1/64, 1/32, and 1/16 under certain conditions, respectively. This can satisfy the precision requirements for large-scale coordinate measurement, and provides a basis for formulating a reasonable light intensity output from a ring-flash in the digital close-range photogrammetry.