How can I randomly sample 10% and 20% pixels of an image

Hello guys

I have an image of size 2,048×2,048 pixels,

I would like to stack the 3 channels to get a matrix of size 6,144 × 2,048.

Then, sample 10% and 20% pixels to construct respectively with sizes each 2048 x 2048 sparse double

pic = double(imread('new4.jpg'));
redChannel = pic(:,:,1);
blueChannel = pic(:,:,2)
greenChannel = pic(:,:,3)

% now my problem is stacking and sampling. Please help!

[Adam Danz]

You can use randsample https://www.mathworks.com/help/stats/randsample.html

and reshape https://www.mathworks.com/help/matlab/ref/reshape.html

or, if you need to extract the red blue green as you've done in the code from your question, you can just use vertical concatenation,

x = [A;B;C];