pmlpp/mlpp/transforms/transforms.cpp

//
//  Transforms.cpp
//
//  Created by Marc Melikyan on 11/13/20.
//

#include "transforms.h"
#include "../lin_alg/lin_alg.h"

#include "core/math/math_funcs.h"

// DCT ii.
// https://www.mathworks.com/help/images/discrete-cosine-transform.html
Ref<MLPPMatrix> MLPPTransforms::discrete_cosine_transform(const Ref<MLPPMatrix> &p_A) {
	Ref<MLPPMatrix> A = p_A->scalar_addn(-128); // Center around 0.

	Size2i size = A->size();

	Ref<MLPPMatrix> B;
	B.instance();
	B->resize(size);

	real_t M = size.y;
	real_t inv_sqrt_M = 1 / Math::sqrt(M);
	real_t s2M = Math::sqrt(real_t(2) / real_t(M));

	for (int i = 0; i < size.y; i++) {
		for (int j = 0; j < size.x; j++) {
			real_t sum = 0;

			real_t alphaI;
			if (i == 0) {
				alphaI = inv_sqrt_M;
			} else {
				alphaI = s2M;
			}

			real_t alphaJ;
			if (j == 0) {
				alphaJ = inv_sqrt_M;
			} else {
				alphaJ = s2M;
			}

			for (int k = 0; k < size.y; k++) {
				for (int f = 0; f < size.x; f++) {
					sum += A->element_get(k, f) * Math::cos((Math_PI * i * (2 * k + 1)) / (2 * M)) * Math::cos((Math_PI * j * (2 * f + 1)) / (2 * M));
				}
			}

			B->element_set(i, j, sum * alphaI * alphaJ);
		}
	}
	return B;
}

void MLPPTransforms::_bind_methods() {
}