A Sharpness Enhancement Using the CSF for HDR Image Rendering

The dynamic range of real-world scenes is broad in the natural world. The high-dynamic-range (HDR) image has pixel values that represent the whole range of real-world scenes. For the reproduction of HDR image, the images having the various exposure times are fused to one HDR image. Many HDR images were rendered by iCAM06 technique, the representative rendering algorithms. Because of the discrete feature of the iCAM06’s fast-bilateral filter, the iCAM06 algorithm may reduce the sharpness of HDR image. This caused that the fast bilateral filter is using a piecewise-linear approximation in the intensity domain and appropriate sub-sampling. In this paper, we proposed a sharpness enhancement technique using the contrast sensitivity function (CSF) for HDR image rendering. Experimental results show that the iCAM06 rendering using CSF has better sharpness property than the default iCAM06 in the human visual system. Fig. 1. Flowchart of iCAM06. iCAM06 for HDR image rendering is shown in Fig. 1. 2.1 Fast bilateral filter In the human visual system (HVS), a local contrast is more sensitive than a global contrast in a real world scene. When compressing the global dynamic range, the local details in the real world scene must be clearly preserved. This is the reason why useful algorithms are needed for preserving local contrast. The base layer in iCAM06 is obtained through a bilateral filter and the detail layer is achieved by subtracting the base layer image from the original image. The bilateral filter preserves the local contrast and avoids the “halo” artifacts [1]. The fast bilateral filtering is speeded up using a piecewise linear approximation and nearest neighbor down sampling in iCAM06 [2].