def update_image_digest(self, image, platform, digest):
        """Update parent image digest for specific platform

        :param ImageName image: image
        :param str platform: name of the platform/arch (x86_64, ppc64le, ...)
        :param str digest: digest of the specified image (sha256:...)
        """
        image_name_tag = self._key(image)

        image_name = image.to_str(tag=False)
        name_digest = '{}@{}'.format(image_name, digest)

        image_digests = self._images_digests.setdefault(image_name_tag, {})
        image_digests[platform] = name_digest