Flash/no-flash fusion for mobile document image binarization

We propose a novel algorithm for improving the quality of binarized document images captured with a mobile device under low light conditions. In such scenarios, images captured without a flash often result in blur artifacts and poor signal-to-noise ratio, while images taken with the flash may produce information loss due to specular reflection in a localized region termed a “flash spot”. Our algorithm automatically triggers the capture of a pair of images, one with and one without flash, in rapid succession. The flash spot region (FSR) is first detected. The two images are then accurately aligned within the FSR using a multiscale alignment technique. Finally the images are binarized and fused in the vicinity of the FSR using an intelligent technique that minimizes fusion boundary artifacts. The result is a binary image that is largely identical to the binarized flash image, except within the FSR where content from the no-flash image is selectively incorporated. To our knowledge this is the first attempt to employ flash/no-flash fusion to improve binarization of mobile document images. Results show superior qualitative and quantitative performance of the proposed algorithm when compared with standard binarization applied to either the flash or no-flash image.