數位攝影機灰度標校正探討

灰度標是用以評估影像中輻射值最大值、最小值、線性度，之慣用工具。對於航空攝影測量使用之製圖型攝影機而言，輻射值是評估影像品質之重要指標之一。一般現場實測作業中，此一項目需有由多個不同灰階之對空標構成之地面設施。其中由最亮到最暗，分成多個不同灰階。國土測繪中心對國內航空遙感探測感應器系統校正制度於民國101年研究案中，以8 階灰度標規劃建置，並以地面光譜儀測量輻射值。配合近於完全散射，且對各波長反射度均等之白板，作為標準件。故而除可比對影像強度值，並可比對反射值。本文就目前測試之8 階灰度標，經實際航空攝影後產製之影像，探討待校件與標準件間影像強度值、反射值之分布與線性度。 A series of targets with stepped grayscale values is the commonly applied means forevaluating the range and linearity of radiance in the image. For the mapping camera used foraerial photogrammetry, the radiance of image is an important subject for the quality measure.In the calibration project carried out by National Land Surveying and Mapping Center, a setof eight targets with stepped grayscale is designed and implemented in 2012. Groundspectrometer is used for measuring the reference radiance. A standard white board whichprovides nearly perfect Lambertian surface is also used to serve as the standard. Therefore, besides the instantaneous radiance, which is weather and time dependent, the reflectance canalso be accessed. In this study, the performance of the camera is calibrated with this setgrayscale targets, and the standard white board.

A series of targets with stepped grayscale values is the commonly applied means forevaluating the range and linearity of radiance in the image. For the mapping camera used foraerial photogrammetry, the radiance of image is an important subject for the quality measure.In the calibration project carried out by National Land Surveying and Mapping Center, a setof eight targets with stepped grayscale is designed and implemented in 2012. Groundspectrometer is used for measuring the reference radiance. A standard white board whichprovides nearly perfect Lambertian surface is also used to serve as the standard. Therefore,besides the instantaneous radiance, which is weather and time dependent, the reflectance canalso be accessed. In this study, the performance of the camera is calibrated with this setgrayscale targets, and the standard white board.