OpenAI gym: How to get pixels in CartPole-v0 - deep-learning

Question

I would like to access the raw pixels in the OpenAI gym CartPole-v0 environment without opening a render window. How do I do this?
Example code:
import gym
env = gym.make("CartPole-v0")
env.reset()
img = env.render(mode='rgb_array', close=True) # Returns None
print(img)
img = env.render(mode='rgb_array', close=False)
# Opens annoying window, but gives me the array that I want
print(img.shape)
PS. I am having a hard time finding good documentation for OpenAI gym. Is it just me, or does it simply not exist?
Edit: I don't need to ever open the render video.

Answer 1

I was curious about same so I started looking into the source code and this is what I found.
Open AI uses pyglet for displaying the window and animations.
For showing the animation everything is drawn on to window and then rendered.
And then pyglet stores what is being displayed on to a buffer.
Dummy version of how code is written in open AI
import pyglet
from pyglet.gl import *
import numpy as np
display = pyglet.canvas.get_display()
screen = display.get_screens()
config = screen[0].get_best_config()
pyglet.window.Window(width=500, height=500, display=display, config=config)
# draw what ever you want
#get image from the buffer
buffer = pyglet.image.get_buffer_manager().get_color_buffer()
image_data=buffer.get_image_data()
arr = np.frombuffer(image_data.get_data(),dtype=np.uint8)
print(arr)
print(arr.shape)
output:
[0 0 0 ... 0 0 0]
(1000000,)
so basically every image we get is from buffer of what is being displayed on the window.
So if we don't draw anything on window we get no image so that window is required to get the image.
so you need to find a way such that windows is not displayed but its values are stored in buffer.
I know its not what you wanted but I hope it might lead you to a solution.

Answer 2

I've just gone through half of the gym source code line by line, and I can tell you that 1, the observation space of cartpole is digits to the ai, not pixels. eg, from their cartpole env py file...
Observation:
Type: Box(4)
Num Observation Min Max
0 Cart Position -2.4 2.4
1 Cart Velocity -Inf Inf
2 Pole Angle -0.209 rad (-12 deg) 0.209 rad (12 deg)
3 Pole Angular Velocity -Inf Inf
So, the pixels are for you at this point. And 2, if your goal is to teach the ai on pixels, you will need to render images from your data-in array, then pass them THROUGH the observation space as a pixel array, like Maunish Dave shows. OpenAI's Atari version does this.
If you want a better guide, don't read the OpenAI Docs, read the Stable Baseline docs here: https://stable-baselines.readthedocs.io/

Answer 3

Someone offers an answer here:
https://github.com/openai/gym/issues/374
"The atari and doom environments give pixels in their observations (ie, the return value from step). I don't think any other ones do.
render produces different results on different OSes, so they're not part of any official environment for benchmarking purposes. But if you want to create a new environment where the observation is in pixels, you could implement it by wrapping an existing environment and calling render."
I'm also working on getting raw pixels as well and I'm trying to find a way to see if what has been returned is what I expect it is.
The documentation can be found:
https://gym.openai.com/docs
And a forum for discussing OpenAI:
discuss.openai.com
Although its not very lively.

Answer 4

I have faced the similar problem:
This is how fixed it, in rendering.py file at /gym/envs/classic_control find the following line in the Viewer class:
self.window = pyglet.window.Window(width=width, height=height, display=display)
Change this line to:
self.window = pyglet.window.Window(width=width, height=height, display=display, visible=False)
Hope it helps!!