/*
* 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;
}
}