'imread' function in MATLAB gives image data.what this image data is?is that intensity of pixels?and how MATLAB computes this data?
'imread' function just read the RGB(in case of color image) or black/white(in case of black and white image) value of each pixel in image and shows it in a matrix format.
it is not 'calculating' these values its just reading them from the image/path you provide to imread function.