size() for images

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Arya k
Arya k 2015-12-13
编辑： DGM 2024-1-19
readImage1=imread(image_file1);
m = size(readImage1);
what does mean by the second line of the code ?

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Stephen23
Stephen23 2015-12-13
编辑：Stephen23 2020-10-29
The size documentation tells us:
" d = size(X) returns the sizes of each dimension of array X in a vector, d, with ndims(X) elements."
You can also very easily try that line in order to find out what it does: load an image and try size and see what it outputs, like this:
>> X = imread('parula_0.png');
>> V = size(X)
V =
420 560 3
This tells us that my image (an array of numbers), is 420 pixels high and 560 pixels across, and contains 3 pages, one for each of R, G and B. It is worth noting that the syntax
[A,B] = size(X);
does NOT return the rows and columns of a 3D (e.g. image) array. Read the size documentation to know why.
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Stephen23
Stephen23 2020-10-29
编辑：Stephen23 2020-10-29
"What do you mean by 3 pages? I dont understand what the third dimension is"
The MATLAB documentation
https://www.mathworks.com/help/matlab/math/multidimensional-arrays.html
defines names for the first three dimensions of an array:
  1. row
  2. column
  3. page
These are the first three dimensions of any array:
X(row,column,page,...)
RGB images are most commonly represented using RxCx3 arrays, where the third dimension encodes the three color channels red, green, and blue:
https://www.mathworks.com/help/matlab/creating_plots/image-types.html
Note that all arrays implicitly have infinite trailing singleton dimensions:
https://blogs.mathworks.com/loren/2006/08/09/essence-of-indexing/

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