Fine rate control and high SNR coding for sparse histogram images

In this report, we propose a lossy compression algorithm which can utilize the `histogram sparseness´ of pixel values of an input image signal. The bit depth of pixel values has becoming longer than conventional ones in high dynamic range images. Their histogram of pixel values tends to be `sparse´, - not all the histogram bins are used. We extend an existing lossless coding based on the histogram packing to a lossy coding, introducing a non-uniform quantization especially for histogram sparse images. It was confirmed that the proposed method attains finer control of the bit rate and also higher SNR in the rate-distortion curve comparing to the existing method.