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Joint Water-Filling Algorithm with Adaptive Chroma Adjustment for Shadow Removal From Text Document Images

With smart portable devices such as smartphones and tablets in usage and popularity, people are more willing to use these devices to scan and save digitized documents. However, when capturing document images, shadows are inevitable and influence clarity and readability. How to remove the shadows of document images is an important and meaningful task. In this paper, we propose a water-filling method using chroma adjustment for shadow removal. Firstly, a global and local jointly water-filling approach is designed to estimate the shading map. Then, we design an adaptive global brightness adjustment strategy to optimize the global luminance of the output image. Since only adjusting brightness can cause color distortion of output images, we propose an adaptive chroma adjustment strategy to ensure color consistency across all areas of output images. A series of experiments show that our method can remove shadows of digitized documents, outperforming some state-of the-art methods. Moreover, the proposed method can keep the brightness and color as consistent as possible with the non-shadow area.