When the Matlab function image displays a matrix with more elements than pixels on a screen how does it decide which matrix elements to display?

I am trying to look for trends in a large data matrix, say 50,000 x 1000 elements. If I use the image command the matrix is printed to the screen. I would like to know how Matlab's image function decides which elements of the matrix to display considering there are not enough pixels on my screen to display so many elements? In other words, which downsampling algorithm is it applying to the matrix?