Photogrammetric exploitation of hdr images for cultural heritage documentation

Abstract

Basic goal of this project is to investigate and therefore highlight the usefulness of High Dynamic Range Images for photogrammetric applications in the field of Cultural Heritage Documentation. Scenes with High Dynamic range – difference between the brightest and the darkest parts – is impossible to be recorded without loss of details and texture in dark areas (due to underexposure) and in bright areas (due to overexposure) because of digital sensor's limitation in high dynamic range recording. In digital recording, the most recent and effective solution is High Dynamic Range Images (HDRI). These images are created by merging multiple images of the same scene, each of which has been taken with different shutter speed and thus providing a better range of images with different exposures. An HDR image alone is overcoming the loss of information caused by unfavorable lighting conditions. In photogrammetric applications, images have to be of high quality and represent faithfully the scene they depict. For applications of Cultural Heritage Documentation, where during image acquisition lighting conditions might be difficult, HDR technology can positively contribute to the acquisition of images of better quality and, consequently, to the creation of orthophotos with no radiometric problems. In this paper, a detailed reference to HDRI technology is made and also the geometric reliability and photogrammetric applicability of HDR images is examined and confirmed. In addition, an example of photogrammetric application in Cultural Heritage Documentation is presented and evaluated.