Usage

To get complete demo of each function, please read the source code (or equivalently API) which is heavily documented and provide a lot of examples in doctest format.

Here is a reduced sample of a common usage scenario:

Instantiation

Let’s create blue color:

>>> from colour import Color
>>> c = Color("blue")
>>> c
<Color blue>

Please note that all of these are equivalent examples to create the red color:

Color("red")  ## human, web compatible representation
Color(red=1)  ## default amount of blue and green is 0.0
Color("blue", hue=0)  ## hue of blue is 0.66, hue of red is 0.0
Color("#f00")  ## standard 3 hex digit web compatible representation
Color("#ff0000")  ## standard 6 hex digit web compatible representation
Color(hue=0, saturation=1, luminance=0.5)
Color(hsl=(0, 1, 0.5))  ## full 3-uple HSL specification
Color(rgb=(1, 0, 0))  ## full 3-uple RGB specification
Color(Color("red"))  ## recursion doesn't break object

Reading values

Several representations are accessible:

>>> c.hex
'#00f'
>>> c.hsl  
(0.66..., 1.0, 0.5)
>>> c.rgb
(0.0, 0.0, 1.0)

And their different parts are also independently accessible, as the different amount of red, blue, green, in the RGB format:

>>> c.red
0.0
>>> c.blue
1.0
>>> c.green
0.0

Or the hue, saturation and luminance of the HSL representation:

>>> c.hue  
0.66...
>>> c.saturation
1.0
>>> c.luminance
0.5

A note on the .hex property, it’ll return the smallest valid value when possible. If you are only interested by the long value, use .hex_l:

>>> c.hex_l
'#0000ff'

Modifying color objects

All of these properties are read/write, so let’s add some red to this color:

>>> c.red = 1
>>> c
<Color magenta>

We might want to de-saturate this color:

>>> c.saturation = 0.5
>>> c
<Color #bf40bf>

And of course, the string conversion will give the web representation which is human, or 3-digit, or 6-digit hex representation depending which is usable:

>>> "%s" % c
'#bf40bf'

>>> c.luminance = 1
>>> "%s" % c
'white'

Ranges of colors

You can get some color scale of variation between two Color objects quite easily. Here, is the color scale of the rainbow between red and blue:

>>> red = Color("red")
>>> blue = Color("blue")
>>> list(red.range_to(blue, 5))
[<Color red>, <Color yellow>, <Color lime>, <Color cyan>, <Color blue>]

Or the different amount of gray between black and white:

>>> black = Color("black")
>>> white = Color("white")
>>> list(black.range_to(white, 6))
[<Color black>, <Color #333>, <Color #666>, <Color #999>, <Color #ccc>, <Color white>]

If you have to create graphical representation with color scale between red and green (‘lime’ color is full green):

>>> lime = Color("lime")
>>> list(red.range_to(lime, 5))
[<Color red>, <Color #ff7f00>, <Color yellow>, <Color chartreuse>, <Color lime>]

Notice how naturally, the yellow is displayed in human format and in the middle of the scale. And that the quite unusual (but compatible) ‘chartreuse’ color specification has been used in place of the hexadecimal representation.

Color comparison

Sane default

Color comparison is a vast subject. However, it might seem quite straightforward for you. Colour uses a configurable default way of comparing color that might suit your needs:

>>> Color("red") == Color("#f00") == Color("blue", hue=0)
True

The default comparison algorithm focuses only on the “web” representation which is equivalent to comparing the long hex representation (e.g. #FF0000) or to be more specific, it is equivalent to compare the amount of red, green, and blue composition of the RGB representation, each of these value being quantized to a 256 value scale.

This default comparison is a practical and convenient way to measure the actual color equivalence on your screen, or in your video card memory.

But this comparison wouldn’t make the difference between a black red, and a black blue, which both are black:

>>> black_red = Color("red", luminance=0)
>>> black_blue = Color("blue", luminance=0)

>>> black_red == black_blue
True

Customization

But, this is not the sole way to compare two colors. As I’m quite lazy, I’m providing you a way to customize it to your needs. Thus:

>>> from colour import RGB_equivalence, HSL_equivalence
>>> Color.equality = staticmethod(HSL_equivalence)
>>> black_red = Color("red", luminance=0)
>>> black_blue = Color("blue", luminance=0)

>>> black_red == black_blue
False

You may also set it per instance:

>>> black_red = Color("red", luminance=0, equality=HSL_equivalence)
>>> black_blue = Color("blue", luminance=0, equality=HSL_equivalence)

>>> black_red == black_blue
False

As you might have already guessed, the sane default is RGB_equivalence, so:

>>> Color.equality = staticmethod(RGB_equivalence)
>>> black_red = Color("red", luminance=0)
>>> black_blue = Color("blue", luminance=0)

>>> black_red == black_blue
True

Here’s how you could implement your unique comparison function:

>>> saturation_equivalence = lambda c1, c2: c1.saturation == c2.saturation
>>> red = Color("red", equality=saturation_equivalence)
>>> blue = Color("blue", equality=saturation_equivalence)
>>> white = Color("white", equality=saturation_equivalence)

>>> red == blue
True
>>> white == red
False

Note: When comparing 2 colors with equality set per instance, only the equality function of the first color will be used. Thus:

>>> black_red = Color("red", luminance=0, equality=RGB_equivalence)
>>> black_blue = Color("blue", luminance=0, equality=HSL_equivalence)

>>> black_red == black_blue
True

But reverse operation is not equivalent !:

>>> black_blue == black_red
False

Equality to non-Colour objects

As a side note, whatever your custom equality function is, it won’t be used if you compare to anything else than a Colour instance:

>>> red = Color("red", equality=lambda c1, c2: True)
>>> blue = Color("blue", equality=lambda c1, c2: True)

Note that these instances would compare as equal to any other color:

>>> red == blue
True

But on another non-Colour object:

>>> red == None
False
>>> red != None
True

Actually, Colour instances will, politely enough, leave the other side of the equality have a chance to decide of the output, (by executing its own __eq__), so:

>>> class OtherColorImplem(object):
...     def __init__(self, color):
...         self.color = color
...     def __eq__(self, other):
...         return self.color == other.web
...

>>> alien_red = OtherColorImplem("red")
>>> red == alien_red
True
>>> blue == alien_red
False

And inequality (using __ne__) are also polite:

>>> class AnotherColorImplem(OtherColorImplem):
...     def __ne__(self, other):
...         return self.color != other.web
...

>>> new_alien_red = AnotherColorImplem("red")
>>> red != new_alien_red
False
>>> blue != new_alien_red
True

Picking arbitrary color for a python object

Basic Usage

Sometimes, you just want to pick a color for an object in your application often to visually identify this object. Thus, the picked color should be the same for same objects, and different for different object:

>>> foo = object()
>>> bar = object()

>>> Color(pick_for=foo)  
<Color ...>
>>> Color(pick_for=foo) == Color(pick_for=foo)
True
>>> Color(pick_for=foo) == Color(pick_for=bar)
False

Of course, although there’s a tiny probability that different strings yield the same color, most of the time, different inputs will produce different colors.

Advanced Usage

You can customize your color picking algorithm by providing a picker. A picker is a callable that takes an object, and returns something that can be instantiated as a color by Color:

>>> my_picker = lambda obj: "red" if isinstance(obj, int) else "blue"
>>> Color(pick_for=3, picker=my_picker, pick_key=None)
<Color red>
>>> Color(pick_for="foo", picker=my_picker, pick_key=None)
<Color blue>

You might want to use a particular picker, but enforce how the picker will identify two object as the same (or not). So there’s a pick_key attribute that is provided and defaults as equivalent of hash method and if hash is not supported by your object, it’ll default to the str of your object salted with the class name.

Thus:

>>> class MyObj(str):
...     pass
...
>>> my_obj_color = Color(pick_for=MyObj("foo"))
>>> my_str_color = Color(pick_for="foo")
>>> my_obj_color == my_str_color
False

Please make sure your object is hashable or “stringable” before using the RGB_color_picker picking mechanism or provide another color picker. Nearly all python object are hashable by default so this shouldn’t be an issue (e.g. instances of object and subclasses are hashable).

Neither hash nor str are perfect solution. So feel free to use pick_key at Color instantiation time to set your way to identify objects, for instance:

>>> a = object()
>>> b = object()
>>> Color(pick_for=a, pick_key=id) == Color(pick_for=b, pick_key=id)
False

When choosing a pick key, you should closely consider if you want your color to be consistent between runs (this is NOT the case with the last example), or consistent with the content of your object if it is a mutable object.

Default value of pick_key and picker ensures that the same color will be attributed to same object between different run on different computer for most python object.

Color factory

As you might have noticed, there are few attributes that you might want to see attached to all of your colors as equality for equality comparison support, or picker, pick_key to configure your object color picker.

You can create a customized Color factory thanks to the make_color_factory:

>>> from colour import make_color_factory, HSL_equivalence, RGB_color_picker

>>> get_color = make_color_factory(
...     equality=HSL_equivalence,
...     picker=RGB_color_picker,
...     pick_key=str,
... )

All color created thanks to CustomColor class instead of the default one would get the specified attributes by default:

>>> black_red = get_color("red", luminance=0)
>>> black_blue = get_color("blue", luminance=0)

Of course, these are always instances of Color class:

>>> isinstance(black_red, Color)
True

Equality was changed from normal defaults, so:

>>> black_red == black_blue
False

This because the default equivalence of Color was set to HSL_equivalence.