(a) input with mixed lighting (daylight + neon under the cabinets + low-energy bulbs on ceiling) exhibits unsightly color casts everywhere (b) naive single-light white balance makes the ceiling white, but other color casts remain (c) user indicates regions that are neutral (white strokes) or correct after the single-light white balance (grey strokes) (d) the image is improved, but color variations can still be observed, e.g., on the wooden cabinet (e) user adds marks to specify uniform color, e.g., the cabinet and the wall (f) our final output with no color casts Figure 1: In this photo, the ambient lighting, the cabinet light, and the ceiling lights all have different colors, which produces unpleasant color casts (a). In such situations, the single-light white balance tool provided in all photo editing software only improves a portion of the image, but the result is not satisfying (b). We address this issue by letting users make annotations on the photo. First, they mark objects of neutral color (i.e., white or gray), and regions that look fine after the standard white balance (c). This improves the result, but undesirable color variations are still visible, e.g., on the cabinetry and on the wall (d). Users can indicate that these elements should have a constant color (e), which yields a result free of color cast (f).
AbstractProper white balance is essential in photographs to eliminate color casts due to illumination. The single-light case is hard to solve automatically but relatively easy for humans. Unfortunately, many scenes contain multiple light sources such as an indoor scene with a window, or when a flash is used in a tungsten-lit room. The light color can then vary on a per-pixel basis and the problem becomes challenging at best, even with advanced image editing tools.We propose a solution to the ill-posed mixed light white balance problem, based on user guidance. Users scribble on a few regions that should have the same color, indicate one or more regions of neutral color , and select regions where the current color looks correct. We first expand the provided scribble groups to more regions using pixel similarity and a robust voting scheme. We formulate the spatially varying white balance problem as a sparse data interpolation problem in which the user scribbles and their extensions form constraints. We demonstrate that our approach can produce satisfying results on a variety of scenes with intuitive scribbles and without any knowledge about the lights.