Down Sample Image by Deleting Alternating Rows & Columns

2022 2 27
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更新时间：2022 2 27
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I am trying to down sample an image to 1/4 and 1/16 its original size, and the instructions are to "use simple decimation to remove every other row and column to do so".
I have been reading through the MATLAB documentation for imresize, downsample, and decimate, as well as various threads here and on other sites, and I cannot seem to figure out how to implement this task?
I = imread('filename');
J = downsample(I,4);
which gives me the correct resize vertically but doesn't change the horizontal dimension. How do I apply this downsample to both rows AND columns?

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Matt J
Matt J 2022-2-27
编辑：Matt J 2022-2-27

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J=I(1:4:end,1:4:end);

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Jason Almeida
Jason Almeida 2022-2-27
编辑：Jason Almeida 2022-2-27
Thanks Matt! I actually figured that out after posting, by looking through the provided code later on in the task, but now I am wondering what the
(1:2:end, 1:2:end,:)
part of the command is representing? That is the portion that was provded (but not explained), so I just want to understand what "1","2", and "end" represent, as well as the ":" as the last term in parenthesis. Even if you (or anyone) could point me to where in the MATLAB documentation I would find this command/info to learn more about its use and syntax?
Matt J
Matt J 2022-2-27
You're welcome. Please Accept-click the answer if it solves your problem.
To read about the 'end' operator and matrix indexing in general, see for example,
https://www.mathworks.com/company/newsletters/articles/matrix-indexing-in-matlab.html

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