问题描述
我使用我认为是矩阵的图像。
I work with an image that I consider as a matrix.
我想将800 x 800矩阵（A）转换为400 x 400矩阵（B ）其中A矩阵的4个单元格的平均值= B矩阵的1个单元格（我知道这不是正确的代码行）：
I want to turn a 800 x 800 matrix (A) into a 400 x 400 matrix (B) where the mean of 4 cells of the A matrix = 1 cell of the B matrix (I know this not a right code line) :
B[1,1] =mean2(A[1,1 + 1,2 + 2,1 + 2,2])
依此类推整个矩阵......
and so on for the whole matrix ...
B [1,2]=mean2(A[1,3 + 1,4 + 2,3 + 2,4 ])
我想：
1）将A矩阵重塑为2 x 320 000矩阵，这样我得到的四个单元格需要彼此相邻，它是之后更容易处理行号。
1) Reshape the A matrix into a 2 x 320 000 matrix so I get the four cells I need to average next to each other and it is easier to deal with the row number afterwards.
Im4bis=reshape(permute(reshape(Im4,size(Im4,2),2,[]),[2,3,1]),2,[]);
2）使用我需要平均（子集化）的4个单元格创建一个单元格数组并计算它的意思。这就是它不起作用的地方
2) Create a cell-array with the 4 cells I need to average (subsetted) and calculate the mean of it. That's where it doesn't work
I{1,160000}=ones,
for k=drange(1:2:319999)
for n=1:160000
I{n}=mean2(Im4bis(1:2,k:k+1));
end
end
我创建了一个400 x 400单元格的空矩阵（实际上是一个1 x 160000的矢量，我想用平均值填充它，但我得到一个1 x 319 999个单元格的矩阵，其中一个单元格为2个空格。
I created an empty matrix of 400 x 400 cells (actually a vector of 1 x 160000) and I wanted to fill it with the mean but I get a matrix of 1 x 319 999 cells with one cell out of 2 empty.
寻找光明
获取循环
out(size(A,1)/2,size(A,2)/2) = 0;
k = 1;
for i = 1:2:size(A,1)
l = 1;
for j = 1:2:size(A,2)
out(k,l) = mean(mean(A(i:i+1,j:j+1)));
l = l+1;
end
k = k+1;
end
测试输入图像：
A = rgb2gray(imread('inputImage.png'));
%// Here, You could use any of the method from any answers
%// or you could use the best method from the bench-marking tests done by Divakar
out = reshape(mean(im2col(A,[2 2],'distinct')),size(A)./2);
imshow(uint8(out));
imwrite(uint8(out),'outputImage.bmp');
输出图片：
最终通过阅读已写入的图像进行检查
Final check by reading the already written image
B = imread('outputImage.bmp');
>> whos B
Name Size Bytes Class Attributes
B 400x400 160000 uint8
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