The demand of digital information compression is increasing dramatically because of the dominance of multimedia technology and the bandwidth limitations of the physical media. The goal of image compression is to represent an image with as few number of bits as possible while preserving the quality required for the given application. JPEG and JPEG2000 are the international standard for still image compression with a fixed quantization matrix. This work presents the impact of varying the elements of this matrix by multiplying and dividing them with integers. The process results in the reduction of the number of bits used to represent the pixels in the compressed image. In this proposed scheme, the trade-off between compression ratio and quality of the image are optimized using Genetic Algorithm. A comparison of the various compression indices are made to validate the proposed method with the benchmark still image 'LENA'.