Essay clarification

I am currently using code to analyse SVS pathology images from Matlab. Aperio ImageScope needs to be downloaded and I can send the annotated images. I have issues with the following code (http://www.andrewjanowczyk.com/working-with-aperio-svs-files-in-matlab-loading-sub-sections/) which states the following "Index exceeds the number of array elements (0).

Error in regionofinterest (line 39)
roi(2:2:4)=roi(2:2:4)*hratio;"