在Matlab中使用逆DCT重建图像的问题

% 示例代码：逆DCT重建图像
I = imread('input.jpg'); % 读取图像
I_dct = dct2(I); % 进行二维DCT变换
I_reconstructed = idct2(I_dct); % 进行逆DCT变换
imshow(I_reconstructed); % 显示重建图像

% 示例代码：使用快速DCT算法
A = dctmtx(8); % 生成8x8的DCT矩阵
I_dct_fast = A * I * A'; % 进行快速DCT变换
I_reconstructed_fast = A' * I_dct_fast * A; % 进行逆DCT变换

% 示例代码：分块处理图像
block_size = 8;
num_blocks_x = size(I, 2) / block_size;
num_blocks_y = size(I, 1) / block_size;
I_reconstructed_block = zeros(size(I));
for i = 1:num_blocks_y
    for j = 1:num_blocks_x
        block = I((i-1)*block_size+1:i*block_size, (j-1)*block_size+1:j*block_size);
        block_dct = dct2(block);
        block_reconstructed = idct2(block_dct);
        I_reconstructed_block((i-1)*block_size+1:i*block_size, (j-1)*block_size+1:j*block_size) = block_reconstructed;
    end
end
imshow(I_reconstructed_block); % 显示重建图像