  In this paper a quaternion approach of enhancement method is proposed in
which color in the image is considered as a single entity. This new method is
referred as the alpha-rooting method of color image enhancement by the
two-dimensional quaternion discrete Fourier transform (2-D QDFT) followed by a
spatial transformation. The results of the proposed color image enhancement
method are compared with its counterpart channel-by-channel enhancement
algorithm by the 2-D DFT. The image enhancements are quantified to the
enhancement measure that is based on visual perception referred as the color
enhancement measure estimation (CEME). The preliminary experiment results show
that the quaternion approach of image enhancement is an effective color image
enhancement technique.
