def download_imagenet(self):
        """ Downloads ImageNet weights and returns path to weights file.
        Weights can be downloaded at https://github.com/fizyr/keras-models/releases .
        """
        if self.backbone == 'vgg16':
            resource = keras.applications.vgg16.vgg16.WEIGHTS_PATH_NO_TOP
            checksum = '6d6bbae143d832006294945121d1f1fc'
        elif self.backbone == 'vgg19':
            resource = keras.applications.vgg19.vgg19.WEIGHTS_PATH_NO_TOP
            checksum = '253f8cb515780f3b799900260a226db6'
        else:
            raise ValueError("Backbone '{}' not recognized.".format(self.backbone))

        return keras.utils.get_file(
            '{}_weights_tf_dim_ordering_tf_kernels_notop.h5'.format(self.backbone),
            resource,
            cache_subdir='models',
            file_hash=checksum
        )
 Downloads ImageNet weights and returns path to weights file.
        Weights can be downloaded at https://github.com/fizyr/keras-models/releases .
        
keras_retinanet/models/vgg.py