This chapter presents methods for color image enhancement based on the discrete quaternion Fourier transform. We choose the quaternion Fourier transform, because it is well-suited for color image processing applications, it processes all three color components (red, green, blue) simultaneously, it captures the inherent correlation between the components, it does not generate color artifacts or blending, and finally, it does not need an additional color restoration process. Also we describe a measure to evaluate the quality of the enhanced color images. Many experimental results show that the a-rooting enhancement based on the quaternion Fourier transform outperforms other enhancement methods such as the Fourier transform based a-rooting algorithm and the multi-scale retinex. On top, the new methods not only provide true color fidelity for poor quality images but also average the color components to gray value for balancing colors. These methods can be used to enhance edge information and sharp features in images, as well as for enhancing low contrast images. The proposed algorithms are simple to apply and design, which makes them very practical in image enhancement.
Online access to SPIE eBooks is limited to subscribing institutions.