1. Systems and Methods for Fast Quaternion Convolution with multimedia;Grigoryan,2016
2. 2-D Left-Side Quaternion Discrete Fourier Transform: Fast Algorithm
3. Tensor representation of color images and fast 2-D quaternion discrete Fourier transform;Grigoryan,2015
4. Carey Bunks, “Grokking the GIMP”, (2000); “5.5. Conversion to grayscale” http://gimpsavvy.com/BOOK/index.html?node54.html.