Flash Lighting Space Sampling

Abstract

Abstract. Flash light of digital cameras is a very useful way to picture scenes with low quality illumination. Nevertheless, especially low-end cameras integrated flash lights are considered as not reliable for high quality images, due to known artifacts (sharp shadows, highlights, uneven lighting) generated in images. Moreover, a mathematical model of this kind of light seems difficult to create. In this paper we present a color correction space which, given some information about the geometry of the pictured scene, is able to provide a space-dependent correction of each pixel of the image. The correction space can be calculated once in a lifetime using a quite fast acquisition procedure; after 3D spatial calibration, obtained color correction function can be applied to every image where flash is the dominant illuminant. The correction space presents several advantages: it is independent from the kind of light used (provided that it is bound to the camera), it gives the possibly to correct only determinate artifacts (for example color deviation) introduced by flash light, and it has a wide range of possible applications, from image enhancement to material color estimation.

Mont’e Scan

“…In contrast to previous work [Dellepiane et al 2009[Dellepiane et al , 2010Levoy et al 2000], we handle images directly in RAW format, which allows us to correct images without prior camera calibration. We experimentally measured that on a medium/high-end camera, such as the Nikon D200 employed in our work, acquisition in RAW format produces images with pixel values proportional to the incoming radiance at medium illumination levels (as also verified elsewhere [Friedrich et al 2010;Kim et al 2012]), and that the flash emits a fairly uniform light within a reasonable working space.…”

“…However, these techniques are hard to use in practice, in typical museum settings with local lights. Dellepiane et al [2009Dellepiane et al [ , 2010 proposed, instead, to use light from camera flashes. They propose to use flash lighting space sampling (FLiSS)-a correction space where a correction matrix is associated to each point in the camera field of view.…”

Improving the digitization of shape and color of 3D artworks in a cluttered environment

“…Since removing lighting artifacts requires knowledge of the lighting environment, one approach is to employ specific techniques that uses probes [26], [27], which are, however, hard to use in practice in a museum setting with local lights. Dellepiane et al [28], [29] proposed, instead to used camera flash light, employing the Flash Lighting Space Sampling (FLiSS), a correction space where a correction matrix is associated to each point in the camera field of view. The method requires a heavy calibration step.…”

“…In contrast to previous work [28], [29], we handle images directly in RAW format, which allows us to correct images also without prior camera calibration. We experimentally measured that, on a medium/high end camera, such as the Nikon D200, RAW data acquisition produces images where each pixel value is proportional to incoming radiance (as also verified elsewhere [30]), and that the flash light emits fairly uniform illumination within a large working space.…”

“…While more accurate results can possibly be obtained with calibration techniques, even the most accurate ones performed off-site [28], [29] do not perfectly match local illumination settings, since indirect illumination is not taken into account. We thus consider this uncalibrated approach to be of practical use.…”