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Description:

pwmlightness 1.0.1

pwm_lightness module
Generates lightness correction tables for eyeball pleasing LED brightness.

Want a smooth fade on your pulsing LEDs? Want antialiasing on LED matrix fonts?
Use this library to correct your raw linear brightness values for human eyeball
persistence of vision perception sensitivity.
The adjustment is otherwise known as the CIE 1931 Lightness
curve.
It is also covered in many
books. The
research was done in the 1920s, winding up as one part of the International
Commission on Illumination (CIE) 1931 standard.
This module does work on CircuitPython (and MicroPython if you build with
floating point enabled). In microcontroller environments recomputing a table
on device is often overkill. Precompute the table(s) you need using this
library and store them as data to save precious RAM.
Smoothly fade an LED
This example assumes CircuitPython or
adafruit-blinka.
import time, board, pulseio, pwm_lightness
PWM = pwm_lightness.get_pwm_table(0xffff, max_input=100)
output_pin = pulseio.PWMOut(board.D13)
while True:
for v in range(100, -1, -1):
output_pin.duty_cycle = PWM[v]
time.sleep(0.02)
for v in range(1, 100):
output_pin.duty_cycle = PWM[v]
time.sleep(0.02)

It is similarly useful with the RGB values you send to programmable LED strips.
Improve antialiased fonts or other 8-bit images
Shown here using Pillow to make an
antialiased font shine rather than appearing as a bold blur:
This example assumes a RPi connected to an I2C Adafruit charlieplexed
LED matrix.
import pwm_lightness
PWM = pwm_lightness.get_pwm_table(60) # 0..255 is our max LED PWM value.
import board, busio, adafruit_is31fl3731, PIL
i2c = busio.I2C(board.SCL, board.SDA)
led_matrix = adafruit_is31fl3731.CharlieBonnet(i2c)
font = PIL.ImageFont.truetype('fonts/RobotoCondensed-Regular.ttf', 16)
image = PIL.Image.new('L', (led_matrix.height, led_matrix.width), 0)
draw = PIL.ImageDraw.Draw(image)
# fill=255 gives us the most antialiasing detail to work with. Control
# brightness using the max_output value passed to get_pwm_table() above.
draw.text((0,-1), '?', fill=255, font=font)
image = image.point(PWM) # Corrects linear 0..255 values for PWM lightness.
image = image.transpose(PIL.Image.ROTATE_90) # Match the matrix orientation.
led_matrix.image(image) # Send pixels to our LED display.