/* * 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; public sealed class NaiveDct { /* * Computes the unscaled DCT type II on the specified array, returning a new array. * The array length can be any value, starting from zero. The returned array has the same length. * For the formula, see https://en.wikipedia.org/wiki/Discrete_cosine_transform#DCT-II . */ public static double[] Transform(double[] vector) { if (vector == null) throw new NullReferenceException(); double[] result = new double[vector.Length]; double factor = Math.PI / vector.Length; for (int i = 0; i < vector.Length; i++) { double sum = 0; for (int j = 0; j < vector.Length; j++) sum += vector[j] * Math.Cos((j + 0.5) * i * factor); result[i] = sum; } return result; } /* * Computes the unscaled DCT type III on the specified array, returning a new array. * The array length can be any value, starting from zero. The returned array has the same length. * For the formula, see https://en.wikipedia.org/wiki/Discrete_cosine_transform#DCT-III . */ public static double[] InverseTransform(double[] vector) { if (vector == null) throw new NullReferenceException(); double[] result = new double[vector.Length]; double factor = Math.PI / vector.Length; for (int i = 0; i < vector.Length; i++) { double sum = vector[0] / 2; for (int j = 1; j < vector.Length; j++) sum += vector[j] * Math.Cos(j * (i + 0.5) * factor); result[i] = sum; } return result; } }