colourettu 0.1.0

Colour related functions

# Colourettu

This is a small collection of colour functions in Python, that can be used to determine the (relative) lumansity 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, however, if you use the American spelling (i.e. without the u), the code should still work. That said, this only applies to the internals of the library, Colourettu will always have the u in it.

~~~python >>> colouretta.colour == colouretta.color True ~~~

## 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 intergers).

~~~python import colourettu

c1 = colourettu.colour() # defaults to #FFF c2 = colourettu.colour(“#eee”) # equivlant 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:

~~~python >>> 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:

~~~python >>> c2.hex() ‘#EEEEEE’ >>> c2.rgb() (238, 238, 238) ~~~

## (Relative) Luminance

Luminance is a meansure 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:

~~~python >>> colourettu.luminance(“#FFF”) # white 0.9999999999999999 >>> colourettu.luminance(“#000”) # black 0.0 ~~~

luminance can also be called on an already existing colour:

~~~python >>> c3.luminance() 0.2641668488934239 >>> colourettu.luminance(c4) ~~~

## Contrast

Contrast the difference in (precieved) 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.

~~~python >>> 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:

~~~python >>> 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 acceissibilty 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 mimimum 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.

~~~python >>> 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

## 0.1.0 – December 11, 2014

• first working version

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