Abstract: In order to convert the existing low dynamic range（LDR） image into the high dynamic range（HDR） image, a method of generating HDR image from a single LDR image is proposed in this paper. Firstly, the input LDR image is decomposed into luminance component and chrominance component based on human visual system, then, constructing the inverse tone mapping operators of this luminance and obtaining its inverse tone mapped image by pixel-wise mapping. Secondly, defining a threshold to sample on the high light areas of the luminance to get a light-source sampled image, and extending the obtained light-source sampled image by Gaussian filter and erosion which can simulate the light attenuation. Thirdly, merging the inverse tone mapped image with the extended high-light-area image by constructing the piece-wise function to get the final luminance. Finally, combining this luminance with the chrominance to generate the HDR image. A plenty of experiments show that the proposed method can get HDR image from a single LDR image with good robustness, which performs better and faster than previous methods.