encode and _encode are identical.
The options argument may be a mapping
containing zero or more encoding options:
normal options:
"compression":Image.TIFF.COMPRESSION_*,
"name":"an image name",
"comment":"an image comment",
"alpha":An alpha channel,
"dpy":Dots per inch (as a float),
"xdpy":Horizontal dots per inch (as a float),
"ydpy":Vertical dots per inch (as a float),