'Integer dots per inch for the height of this image. Defaults to 72
when not present in the file, as is often the case.'

@property
def vert_dpi(self):

    pHYs = self._chunks.pHYs
    if (pHYs is None):
        return 72
    return self._dpi(pHYs.units_specifier, pHYs.vert_px_per_unit)
