Image bit-depth enhancement via maximum-a-posteriori estimation of graph AC component
Image bit-depth enhancement via maximum-a-posteriori estimation of graph AC component
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DOI：
10.1109/icip.2014.7025823
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发表时间：
2014-10
期刊：
影响因子：
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通讯作者：
Pengfei Wan;Gene Cheung;D. Florêncio;Cha Zhang;O. Au
中科院分区：
文献类型：
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作者：
Pengfei Wan;Gene Cheung;D. Florêncio;Cha Zhang;O. Au
虽然现代显示器为每个渲染像素提供高动态范围（HDR）和大位深，但大部分遗留图像和视频内容是使用较浅位深的相机拍摄的。本文研究了图像的位深度增强问题，以便从输入的低位深度（LBD）图像重构出高位深度（HBD）图像。关键思想是在给定重构信号必须位于每像素量化箱的约束下应用适当的平滑。具体来说，我们首先通过信号相关图拉普拉斯定义平滑，这样自然图像梯度仍然可以被解释为低频。给定定义的平滑先验和观察到的LBD图像，我们然后证明，通过最大后验（MAP）估计计算最可能的信号可能导致很大的预期失真。然而，我们认为MAP仍然可以用来有效地估计期望的HBD信号的交流分量，它与失真最小化的直流分量一起，可以产生一个很好的近似解，使期望的失真最小化。实验结果表明，该方法在重构误差方面优于现有的位深度增强方法。
While modern displays offer high dynamic range (HDR) with large bit-depth for each rendered pixel, the bulk of legacy image and video contents were captured using cameras with shallower bit-depth. In this paper, we study the bit-depth enhancement problem for images, so that a high bit-depth (HBD) image can be reconstructed from an input low bit-depth (LBD) image. The key idea is to apply appropriate smoothing given the constraints that reconstructed signal must lie within the per-pixel quantization bins. Specifically, we first define smoothness via a signal-dependent graph Laplacian, so that natural image gradients can nonetheless be interpreted as low frequencies. Given defined smoothness prior and observed LBD image, we then demonstrate that computing the most probable signal via maximum a posteriori (MAP) estimation can lead to large expected distortion. However, we argue that MAP can still be used to efficiently estimate the AC component of the desired HBD signal, which along with a distortion-minimizing DC component, can result in a good approximate solution that minimizes the expected distortion. Experimental results show that our proposed method outperforms existing bit-depth enhancement methods in terms of reconstruction error.