Abstract
A novel set of fractional orthogonal polar harmonic transforms for gray-scale and color image analysis are presented in this paper. These transforms are divided into two groups. The first group contains fractional polar complex exponential transforms (FrPCETs), fractional polar cosine transforms (FrPCTs), and fractional polar sine transforms (FrPSTs) for gray-scale images. The second group contains the fractional quaternion polar complex exponential transforms (FrQPCETs), fractional quaternion polar cosine transforms (FrQPCTs), and fractional quaternion polar sine transforms (FrQPSTs) for color images. All mathematical formulae for the basis functions, orthogonality relations and reconstruction forms are derived and their validity are proved. The required mathematical forms for invariance to rotation, scaling and translation (RST) are derived. A series of experiments is performed to test the validity of the proposed fractional polar harmonic transforms (FrPHTs) and the fractional quaternion polar harmonic transforms (FrQPHTs). The performances of the proposed FrPHTs and FrQPHTs are outperformed the classical polar harmonic transforms, the quaternion polar harmonic transforms and the existing fractional orthogonal transforms in terms of accuracy and numerical stability, digital image reconstruction, RST invariances, robustness to noise and computational efficiency. (C) 2020 The Franklin Institute. Published by Elsevier Ltd. All rights reserved.