example resize

This resizes an image to within a bounding box. Make the first parameter very large to just scale to height.

def resize(filein, fileout, maxw, maxh):
    im = pyvips.Image.new_from_file(filein, access="sequential")
    out = pyvips.Image.thumbnail(filein, maxw, height=maxh)
    out.write_to_file(fileout , Q=95)

it uses the thumbnail thumbnail function of vips - which has a lot of features (and doesn't just make thumbnails)