size() for images

readImage1=imread(image_file1);

m = size(readImage1);

what does mean by the second line of the code ?

[Gopolang]

the dimensions of the image

Answer 1

[Stephen23]

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.

[jamie c]

What do you mean by 3 pages? I dont understand what the third dimension is

[Stephen23]

"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/

[DGM]

See also:

https://blogs.mathworks.com/steve/2011/03/22/too-much-information-about-the-size-function/

https://blogs.mathworks.com/steve/2011/03/29/even-more-information-about-the-size-function/