问题描述
我使用 1D DCT 和 IDCT 实现了我自己的 2D DCT。我的 DCT 结果与 Matlab 的实现相匹配,但 IDCT 给出了不同的结果。从重建图像中可以看出,差异并非完全消失。
解决方法
我对此有所了解 - 您的 DCT/IDCT 方程在我看来不太合适。我使用了 SciPy 文档 here 中的 DCT-2 和 DCT-3 公式。
original_img = imread('nggyu.jpeg');
transformed_img = permute(dct1d(permute( ...
dct1d(double(original_img)),...
[2,1,3])),[2,3]);
recovered_img = uint8(permute(idct1d(permute( ...
idct1d(transformed_img),...
[2,3]));
figure('position',[0,600,200])
subplot(1,3,1),imshow(original_img),title 'Original'
subplot(1,2),imshow(log(abs(transformed_img)),[]),title 'DCT'
subplot(1,3),imshow(recovered_img),title 'IDCT'
function y = dct1d(x)
% Compute normalized DCT-2 over the first dimension of the input.
N = size(x,1);
y = zeros(size(x));
n = (1:N)';
for k = 1:N
if k == 1
scale = sqrt(1/(4*N));
else
scale = sqrt(1/(2*N));
end
y(k,:,:) = scale * 2 * sum(x(n,:) .* cos((pi/(2*N)) * (2*n-1) * (k-1)),1);
end
end
function x = idct1d(y)
% Compute normalized DCT-3 over the first dimension of the input.
N = size(y,1);
x = zeros(size(y));
k = (2:N)';
for n = 1:N
x(n,:) = y(1,:)/sqrt(N) + sqrt(2/N) * sum(y(k,1);
end
end