colourettu 1.0.0

Colour related functions

Colourettu is a small collection of colour functions in Python, that can be used to determine the (relative) luminosity of a colour and the contrast between two colours.

Installation

pip install colourettu

Note on Spelling

I have used the Canadian/British spelling of colour through this and the code.

Links

• Code, on GitHub: http://www.github.com/minchinweb/colourettu/

• Report a Bug! https://github.com/minchinweb/colourettu/issues

• Documentation: http://minchin.ca/colourettu/

• Listing on PyPI: https://pypi.python.org/pypi/colourettu

License

Colourettu is licensed under the MIT license.

Colour Class

Colours are created by calling the colour class. Colour values can be provided via 3 or 6 digit hex notation, or providing a list or a tuple of the Red, Green, and Blue values (as integers).

import colourettu

c1 = colourettu.colour()        # defaults to #FFF
c2 = colourettu.colour("#eee")  # equivalent to #EEEEEE
c3 = colourettu.colour("#456bda")
c4 = colourettu.colour([3, 56, 129])
c5 = colourettu.colour((63, 199, 233))

The value of each channel can be pulled out:

>>> c4.red()
3
>>> c4.green()
56
>>> c4.blue()
129

You can also get the colour back as either a hex value, or a rgb tuple:

>>> c2.hex()
'#EEEEEE'
>>> c2.rgb()
(238, 238, 238)

(Relative) Luminance

Luminance is a measure of how ‘bright’ a colour is. Values are normalized so that the Luminance of White is 1 and the Luminance of Black is 0. That is to say:

>>> colourettu.luminance("#FFF")    # white
0.9999999999999999
>>> colourettu.luminance("#000")    # black
0.0

luminance can also be called on an already existing colour:

>>> c3.luminance()
0.2641668488934239
>>> colourettu.luminance(c4)
0.08007571268096524

Contrast

Contrast the difference in (perceived) brightness between colours. Values vary between 1:1 (a given colour on itself) and 21:1 (white on black).

To compute contrast, two colours are required.

>>> colourettu.contrast("#FFF", "#FFF") # white on white
1.0
>>> colourettu.contrast(c1, "#000") # black on white
20.999999999999996
>>> colourettu.contrast(c4, c5)
4.363552233203198

contrast can also be called on an already existing colour, but a second colour needs to be provided:

>>> c4.contrast(c5)
4.363552233203198

Use of Contrast

For Basic readability, the ANSI standard is a contrast of 3:1 between the text and it’s background. The W3C proposes this as a minimum accessibility standard for regular text under 18pt and bold text under 14pt. This is referred to as the A standard. The W3C defines a higher AA standard with a minimum contrast of 4.5:1. This is approximately equivalent to 20/40 vision, and is common for those over 80. The W3C define an even higher AAA standard with a 7:1 minimum contrast. This would be equivalent to 20/80 vision. Generally, it is assumed that those with vision beyond this would access the web with the use of assistive technologies.

If needed, these constants are stored in the library.

>>> colourettu.A_contrast
3.0
>>> colourettu.AA_contrast
4.5
>>> colourettu.AAA_contrast
7.0

I’ve also found mention that if the contrast is too great, this can also cause readability problems when reading longer passages. This is confirmed by personal experience, but I have been (yet) unable to find any quantitative research to this effect.

Changelog

Changelog for Colourettu

1.0.0 – unreleased

• documentation is now online at minchin.ca/colourettu

• convert Readme and Changelog from Markdown to ReStructured Text

• colourettu.color (note, no u) no longer an alais for colourettu.colour (with the u)

0.1.1 – December 11, 2014

• include extra files so module can install off of pip

0.1.0 – December 11, 2014

• first working version

• includes base colour class, and (relative) luminance and contrast functions