How i generate dataset from the source image for running ExtraTrees Ensemble

I have Matlab Code of Extremely randomized Tree ensemble(MATLAB_ExtraTrees) which works on the dataset that was generated by an equation Y = 0.5 * X(:,1) - 0.2 * X(:,2) + 0.1 * X(:,3) + 0.05 * randn(n,1); where n=500 observations and X = randn(n,3); But i want to run this code for a heart CT images and didn't get a point how i generate my dataset from the images for this code.As i am new in Matlab and having little knowledge about Machine learning.

Please help me in this regard.

Thanks