rpi-rgb-led-matrix/python

Python bindings for RGB Matrix library

Building

In the root directory for the matrix library simply type:

sudo apt-get update && sudo apt-get install python2.7-dev python-pillow -y
make build-python
sudo make install-python

You can also build for Python 3:

sudo apt-get update && sudo apt-get install python3-dev python3-pillow -y
make build-python PYTHON=$(which python3)
sudo make install-python PYTHON=$(which python3)

Speed

The simplicity of scripting comes at a price: Python is slower than C++ of course. If you have to do a lot of pixel updates in your demo, this can be too slow depending on what you do. Here are some rough numbers:

• On a Pi-2 and Pi-3, a Python script will be about 1/5 of the speed compared to the corresponding C++ program (pushing 0.5 Megapixels/s Python vs. 2.5 Megapixels/s C++ on a Pi-3 for instance)
• On a Pi-1, the difference is even worse: 1/17 of the speed to the corresponding C++ program. Given that the Pi-1 is already about 1/10 the speed of a Pi-3, this almost makes Python unusable on a Pi-1 (0.017 Megapixels/s Python vs. 0.3 Megapixels/s C++)
• Also interesting: Python3 is about 40% slower than Python2.7 (measured on a Pi-3). So if you can, stick with Python2.7 for now.

The 0.017 Megapixels/s on a Pi-1 means that you can update a 32x32 matrix at most with 17Hz. If you have chained 5, then you barely reach 3.5Hz. In a Pi-3, you get about 450Hz update rate (90Hz for 5-chain) with a Python program (while with C++, you can do the same thing with a comfortable 2600Hz (520Hz for 5)). Keep in mind that this is just the time calling SetPixel(), it does not include any time yet of what you actually want to do in your demo - so anything in addition to that will drop your update rate.

Using the library

Be aware of the fact, that using the RGBMatrix requires root privileges. Therefore you will need to run all you python scripts as using sudo.

You find examples in the samples/ subdirectory.

Here a complete example how to write an image viewer:

#!/usr/bin/env python
import time
import sys

from rgbmatrix import RGBMatrix
from PIL import Image

if len(sys.argv) < 2:
    sys.exit("Require an image argument")
else:
    image_file = sys.argv[1]

image = Image.open(image_file)

rows = 32
chain = 1
parallel = 1
matrix = RGBMatrix(rows, chain, parallel)

# Make image fit our screen.
image.thumbnail((matrix.width, matrix.height), Image.ANTIALIAS)

matrix.SetImage(image.convert('RGB'))

try:
    print("Press CTRL-C to stop.")
    while True:
        time.sleep(100)
except KeyboardInterrupt:
    sys.exit(0)