DCT-Based Color Image Compression Algorithm using an Efficient Lossless Encoder

To enhance the compression ratio of color still image compression, this paper proposes an efficient lossy image compression algorithm using a new efficient lossless encoder. Firstly, the pre-processing, including mean removing and YCbCr transform, is applied to image. Then, this paper applies discrete cosine transform (DCT) to reduce spatial correlation and concentrate the energy of the image. An iterative process based on the bisection method is used to determine the required threshold and control compression quality via achieving the prefixed peak signal-to-noise ratio (PSNR). The next step is applying adaptive scanning to each transform coefficient block to get better compression performance. The final step is the application of a modified lossless encoder to optimize the compression algorithm according to the statistical characteristics of the DCT coefficients. The format of modified encoder is suitable for entropy encoding. Compared with other two algorithms, the experimental results show that the proposed algorithm has better performance in terms of subjective and objective evaluation.

Keywords: color image compression; discrete cosine transform (DCT); YCbCr transform; adaptive scanning; lossless encoder