Asterix#

../../../_images/asterix.gif

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

Action Space

Discrete(9)

Observation Shape

(210, 160, 3)

Observation High

255

Observation Low

0

Import

gymnasium.make("ALE/Asterix-v5")

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

Description#

You are Asterix and can move horizontally (continuously) and vertically (discretely). Objects move horizontally across the screen: lyres and other (more useful) objects. Your goal is to guideAsterix in such a way as to avoid lyres and collect as many other objects as possible. You score points by collecting objects and lose a life whenever you collect a lyre. You have three lives available at the beginning. If you score sufficiently many points, you will be awarded additional points.

For a more detailed documentation, see the AtariAge page

Actions#

Asterix has the action space Discrete(9) with the table below lists the meaning of each action’s meanings. As Asterix uses a reduced set of actions for v0, v4 and v5 versions of the environment. 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

UP

2

RIGHT

3

LEFT

4

DOWN

5

UPRIGHT

6

UPLEFT

7

DOWNRIGHT

8

DOWNLEFT

Observations#

Atari environment have two possible observation types, the observation space is listed below. See variants section for the type of observation used by each environment id.

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

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

Additionally, obs_type="grayscale" cause the environment return a grayscale version of the rgb array for observations with the observation space being Box(0, 255, (210, 160), np.uint8)

Rewards#

A table of scores awarded for collecting the different objects is provided on the AtariAge page.

Variants#

Asterix 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=

Asterix-v0

"rgb"

(2, 5)

0.25

Asterix-ram-v0

"ram"

(2, 5)

0.25

Asterix-ramDeterministic-v0

"ram"

4

0.25

Asterix-ramNoFrameskip-v0

"ram"

1

0.25

AsterixDeterministic-v0

"rgb"

4

0.25

AsterixNoFrameskip-v0

"rgb"

1

0.25

Asterix-v4

"rgb"

(2, 5)

0.0

Asterix-ram-v4

"ram"

(2, 5)

0.0

Asterix-ramDeterministic-v4

"ram"

4

0.0

Asterix-ramNoFrameskip-v4

"ram"

1

0.0

AsterixDeterministic-v4

"rgb"

4

0.0

AsterixNoFrameskip-v4

"rgb"

1

0.0

ALE/Asterix-v5

"rgb"

4

0.25

ALE/Asterix-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

[0]

0

[0]

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