/* * Fast discrete cosine transform algorithms (C#) * * Copyright (c) 2017 Project Nayuki. (MIT License) * https://www.nayuki.io/page/fast-discrete-cosine-transform-algorithms * * Permission is hereby granted, free of charge, to any person obtaining a copy of * this software and associated documentation files (the "Software"), to deal in * the Software without restriction, including without limitation the rights to * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of * the Software, and to permit persons to whom the Software is furnished to do so, * subject to the following conditions: * - The above copyright notice and this permission notice shall be included in * all copies or substantial portions of the Software. * - The Software is provided "as is", without warranty of any kind, express or * implied, including but not limited to the warranties of merchantability, * fitness for a particular purpose and noninfringement. In no event shall the * authors or copyright holders be liable for any claim, damages or other * liability, whether in an action of contract, tort or otherwise, arising from, * out of or in connection with the Software or the use or other dealings in the * Software. */ using System; using System.Numerics; public sealed class FastDctFft { /* * Computes the unscaled DCT type II on the specified array in place. * The array length must be a power of 2 or zero. * For the formula, see https://en.wikipedia.org/wiki/Discrete_cosine_transform#DCT-II . */ public static void Transform(double[] vector) { if (vector == null) throw new NullReferenceException(); int len = vector.Length; int halfLen = len / 2; Complex[] temp = new Complex[len]; for (int i = 0; i < halfLen; i++) { temp[i] = vector[i * 2]; temp[len - 1 - i] = vector[i * 2 + 1]; } if (len % 2 == 1) temp[halfLen] = vector[len - 1]; Fft.Transform(temp, false); for (int i = 0; i < len; i++) vector[i] = (temp[i] * Complex.Exp(new Complex(0, -i * Math.PI / (len * 2)))).Real; } /* * Computes the unscaled DCT type III on the specified array in place. * The array length must be a power of 2 or zero. * For the formula, see https://en.wikipedia.org/wiki/Discrete_cosine_transform#DCT-III . */ public static void InverseTransform(double[] vector) { if (vector == null) throw new NullReferenceException(); int len = vector.Length; if (len > 0) vector[0] /= 2; Complex[] temp = new Complex[len]; for (int i = 0; i < len; i++) temp[i] = vector[i] * Complex.Exp(new Complex(0, -i * Math.PI / (len * 2))); Fft.Transform(temp, false); int halfLen = len / 2; for (int i = 0; i < halfLen; i++) { vector[i * 2 + 0] = temp[i].Real; vector[i * 2 + 1] = temp[len - 1 - i].Real; } if (len % 2 == 1) vector[len - 1] = temp[halfLen].Real; } }