Galaxian

This environment is part of the Atari environments. Please read that page first for general information.

Action Space	Discrete(6)
Observation Space	Box(0, 255, (210, 160, 3), uint8)
Import	gymnasium.make("ALE/Galaxian-v5")

For more Galaxian variants with different observation and action spaces, see the variants section.

Description

Protect your laser base from a Galaxian invasion. Defeat each wave by firing lasers at the attackers.

For a more detailed documentation, see the AtariAge page

Actions

Galaxian has the action space of Discrete(6) with the table below listing the meaning of each action’s meanings. To enable all 18 possible actions that can be performed on an Atari 2600, specify full_action_space=True during initialization or by passing full_action_space=True to gymnasium.make.

Value	Meaning	Value	Meaning	Value	Meaning
0	NOOP	1	FIRE	2	RIGHT
3	LEFT	4	RIGHTFIRE	5	LEFTFIRE

Observations

Atari environments have three possible observation types: "rgb", "grayscale" and "ram".

• obs_type="rgb" -> observation_space=Box(0, 255, (210, 160, 3), np.uint8)

• obs_type="ram" -> observation_space=Box(0, 255, (128,), np.uint8)

• obs_type="grayscale" -> Box(0, 255, (210, 160), np.uint8), a grayscale version of the “rgb” type

See variants section for the type of observation used by each environment id by default.

Variants

Galaxian has the following variants of the environment id which have the following differences in observation, the number of frame-skips and the repeat action probability.

Env-id	obs_type=	frameskip=	repeat_action_probability=
ALE/Galaxian-v5	"rgb"	4	0.25
ALE/Galaxian-ram-v5	"ram"	4	0.25

Difficulty and modes

It is possible to specify various flavors of the environment via the keyword arguments difficulty and mode. A flavor is a combination of a game mode and a difficulty setting. The table below lists the possible difficulty and mode values along with the default values.

Available Modes	Default Mode	Available Difficulties	Default Difficulty
[1, ..., 9]	1	[0, 1]	0

Version History

A thorough discussion of the intricate differences between the versions and configurations can be found in the general article on Atari environments.

• v5: Stickiness was added back and stochastic frameskipping was removed. The environments are now in the “ALE” namespace.

• v4: Stickiness of actions was removed

• v0: Initial versions release