The purpose of image enhancement is to improve the quality of a digital image, so as to support the human perception. In this paper, new methods of image enhancement are proposed for enhancement of color images, which are based on application of the concept of the two-dimensional quaternion discrete Fourier transform (QDFT) together with the well-known method of the alpha-rooting. The application of the alpha-rooting method which is based on the traditional two-dimensional discrete Fourier transform (2-D DFT) results in high quality images, when comparing with other transforms, such as Hadamard, Hartley, cosine, and heap transforms. The image enhancement technique of alpha-rooting can be used for enhancing even low contrast images. In zonal alpha-rooting method, the modification of frequency is different for different frequency zones. Optimization of alpha value is done with genetic algorithm.