This is one of the example scripts included with Shady. These scripts can be run conventionally like any normal Python script, or you can choose to run them as interactive tutorials, for example with python -m Shady demo interactive-gamma

#!/usr/bin/env python
# This file is part of the Shady project, a Python framework for
# real-time manipulation of psychophysical stimuli for vision science.
# Copyright (c) 2017-2020 Jeremy Hill, Scott Mooney
# Shady is free software: you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with this program. If not, see http://www.gnu.org/licenses/ .

#: Demonstrates an interactive perceptual-linearization tool
This script demonstrates the `FindGamma()` utility function.
It creates a `LinearizationTestPattern()` stimulus, displays it,
and then installs an `EventHandler` that allows interactive gamma
adjustment with the mouse or touchscreen.

This demo requires the third-party package `numpy`, used in the
generation of the `LinearizationTestPattern()`.
if __name__ == '__main__':

	import Shady

	Parse command-line options:
	cmdline = Shady.WorldConstructorCommandLine( canvas=True )
	gamma = cmdline.Option( 'gamma',  1.0, type=( int, float, tuple, list ), doc='Start value(s) for exponent `.gamma` that should be corrected-for.' )
	xBlue = cmdline.Option( 'xblue', True, type=bool, container=None, doc='Whether or not to adjust blue gamma separately, relative to the others, with horizontal movement.' )
	text  = cmdline.Option( 'text', True, type=bool, container=None, doc='Whether or show the gamma values as text on screen.' )
	Shady.Require( 'numpy' ) # die with an informative error if this is missing

	Create a `World`, along with a `Stimulus` that might benefit
	from linearization:
	world = Shady.World( **cmdline.opts )
	gabor = world.Sine(
		size = min( world.width / 2, world.height ) * 0.75,
		x = -world.width / 4,
		plateauProportion = 0,
		signalFrequency = 0.01,   # 100 pixels per cycle
		cx = lambda t: t * 100,   # 100 pixels per second
		contrast = Shady.Oscillator( 0.2 ) * 0.5 + 0.5,
	# NB: The `w.Sine()` method is a wrapper around `w.Stimulus`.
	#     Among other settings, it yokes the Stimulus `.gamma`
	#     (and other "atmosphere" properties) to the corresponding
	#     properties of the `World`

	redgreen = world.Sine().Inherit( gabor ).Set(
		x = world.width / 4,
		color = [ 1, 0, 0.15 ],  # signal function output will be multiplied by this vector
	First we'll define a callback function to handle the gamma value
	that is found by the interactive adjustment procedure.  The callback
	must handle the possibility that its input argument is `None` (which
	is what happens when the user presses the escape key).
	def finish( finalGamma ):
		if finalGamma is None:
			print( '\nNo change: world.gamma is still %r' % list( world.gamma ) )
			print( '\nSetting world.gamma = %r' % list( finalGamma ) )
			world.gamma = finalGamma
	You can call `Shady.FindGamma()` quite straightforwardly yourself.	
	But for the purposes of this demo, we'll add another layer of complexity:
	we'll set up an `EventHandler` such that `Shady.FindGamma()` gets
	launched every time you hit the enter/return key:
	@world.EventHandler( slot=-1 )
	def PressReturnToStartAdjusting( self, event ):
		if event.type == 'key_release' and event.key in [ 'enter', 'return' ]:
			Shady.FindGamma( world, xBlue=xBlue, finish=finish, text=text )
	print( """
Press the enter/return key to display the linearization pattern and
start adjusting gamma.

While adjusting:

- press enter/return again to finish adjusting and adopt the new settings;
- press escape to exit the adjustment without adopting the new settings;
- press any letter key to report the current gamma setting to the console.
""" )
	Shady.AutoFinish( world )