At self.im_info["gamma"] = 1 / 2.2, self.im_info has never been initialized and so trying to set self.im_info["gamma"] fails with:

AttributeError: 'DdsImageFile' object has no attribute 'im_info'

As far as I can tell, this is the only place im_info is ever referenced in this or the ancestor classes.

A possible solution would be to change this section to:

                elif dxgi_format == DXGI_FORMAT_BC7_UNORM_SRGB:
                    self.pixel_format = "BC7"
                    if not hasattr(self, 'im_info'):
                        self.im_info = {}
                    self.im_info["gamma"] = 1 / 2.2
                    n = 7

An alternate solution would be to initialize im_info earlier in the loader method.