class ExtendedImageField(models.ImageField):
    """
    Extended ImageField which can resize image before saving it.
    """

    def __init__(self, *args, **kwargs):
        self.width = kwargs.pop('width', None)
        self.height = kwargs.pop('height', None)
        super(ExtendedImageField,self).__init__(*args, **kwargs)


    def get_save_FIELD_file(self):
        def _save_FIELD_file(instance, filename, raw_contents, save=True):
            """
            Resize on the fly raw contents of field and call parent save_field
            method.
            """

            if self.width and self.height:
                raw_contents  = resize_image(rawdata=raw_contents, width=self.width, height=self.height)
                filename_ext = filename.split(".")[-1:]
                filename_name = md5.new(str(time.time())).hexdigest()
                filename = "%s.%s" % (filename_name, filename_ext)
            instance._save_FIELD_file(self, filename, raw_contents, save)
        return _save_FIELD_file


    def contribute_to_class(self, cls, name):
        super(ExtendedImageField, self).contribute_to_class(cls, name)
        # overwrite parent binding to 'save_%s_file'
        setattr(cls, 'save_%s_file' % self.name, self.get_save_FIELD_file())


    def get_internal_type(self):
        return 'ImageField'