DCT-based compression algorithm using reduced adaptive block scanning for color image

This paper presents a lossy image compression algorithm dedicated to color still images. Based on DCT, the proposed method utilizes a simple technique to encode efficiently the DCT coefficients. After the step of the RGB to YCbCr transformation, the DCT transform is applied. The desired quality is assured by using the bisection method to threshold the quantized DCT coefficients. Two scan orders (zigzag and vertical) are used to read the DCT coefficients from the retained DCT block coefficients. Following a scan order, an index vector is formed by the length of the zero-run sequence that preceded a nonzero DCT coefficient. The lowest value of the two index vectors maximums determines the best scan. Finally, the nonzero DCT coefficients and the index vector for each block are encoded to form the compressed image. When compared with recent methods, the obtained results show that the proposed algorithm achieves high performance.