Source code for pyface.util.color_helpers

# (C) Copyright 2005-2022 Enthought, Inc., Austin, TX
# All rights reserved.
#
# This software is provided without warranty under the terms of the BSD
# license included in LICENSE.txt and may be redistributed only under
# the conditions described in the aforementioned license. The license
# is also available online at http://www.enthought.com/licenses/BSD.txt
#
# Thanks for using Enthought open source!

""" Routines supporting color computations

Most of what is needed is provided by Python's builtin colorsys module,
but we need a few additional routines for things that are not covered by
that code.
"""


[docs]def channels_to_ints(channels, maximum=255): """ Convert an iterable of floating point channel values to integers. Values are rounded to the nearest integer, rather than truncated. Parameters ---------- channels : iterable of float An iterable of channel values, each value between 0.0 and 1.0, inclusive. maximum : int The maximum value of the integer range. Common values are 15, 65535 or 255, which is the default. Returns ------- values : tuple of int A tuple of values as integers between 0 and max, inclusive. """ return tuple(int(round(channel * maximum)) for channel in channels)
[docs]def ints_to_channels(values, maximum=255): """ Convert an iterable of integers to floating point channel values. Parameters ---------- values : tuple of int An iterable of values as integers between 0 and max, inclusive. maximum : int The maximum value of the integer range. Common values are 15, 65535 or 255, which is the default. Returns ------- channels : iterable of float A tuple of channel values, each value between 0.0 and 1.0, inclusive. """ return tuple(value / maximum for value in values)
[docs]def relative_luminance(rgb): """ The relative luminance of the color. This value is the critical value when comparing colors for contrast when displayed next to each other, in particular for readability of text. Parameters ---------- rgb : tuple of red, green, blue values A tuple of values representing red, green and blue components of the color, as values from 0.0 to 1.0. Returns ------- luminance : float The relative luminance of the color. References ---------- Web Contrast Accessibility Guidelines https://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef """ gamma_corrected = [ x/12.92 if x <= 0.03928 else ((x + 0.055)/1.055)**2.4 for x in rgb ] luminance = ( 0.2126 * gamma_corrected[0] + 0.7152 * gamma_corrected[1] + 0.0722 * gamma_corrected[2] ) return luminance
[docs]def is_dark(rgb): """ Is the color dark to human perception? A color is dark if white contasts better with it according to the WC3 definition of contrast ratio. This is allows GUI code to choose either black or white as a contrasting color for things like text on a colored background. Parameters ---------- rgb : tuple of red, green, blue values A tuple of values representing red, green and blue components of the color, as values from 0.0 to 1.0. References ---------- Understanding Web Contrast Accessibility Guidelines https://www.w3.org/TR/UNDERSTANDING-WCAG20/visual-audio-contrast-contrast.html#contrast-ratiodef """ lumininance = relative_luminance(rgb) black_contrast = (lumininance + 0.05) / 0.05 white_contrast = 1.05 / (lumininance + 0.05) return white_contrast > black_contrast