If your mouse has a wheel, this will do the zooming. If not, shift-left-click zooms in, while ctrl-left-click zooms out. The coding allows the initial size of the image in its window to be specified, as well as the maximum size (here 100%) and the minimum size (here 20%). This image is 10.2 megapixels - over 2.12Mb - and may not load, or do so easily...