# Color addon

These functions are declared in the following header file.
Link with allegro_color.

~~~~c
 #include <allegro5/allegro_color.h>
~~~~

When converting between certain color spaces, RGB colors are implicitly
assumed to mean sRGB.

sRGB is a standard which maps RGB colors to absolute colors. sRGB is
very close to RGB values on a monitor which has a gamma value of 2.2.
For example when the red component of a color is 0.5, the monitor will
use a brightness of pow(0.5, 2.2) or about 22% - and not 50%. The reason
is that human eyes can distinguish better between dark colors than
between bright colors, and so if a pixel of the monitor is lit up to
22% of its maximum power it already will appear at half brightness to a
human eye.

sRGB improves upon simple gamma correction by taking differences
between the three color channels into account as well. In general, most
monitors nowadays try to be close to the sRGB specification. And so if
in an Allegro game you display something with color

al_map_rgb_f(0.5, 0.5, 0,5)

then it will appear at about half brightness (even though the actual
brightness output of the monitor will be less than half).


## API: al_color_cmyk

Return an [ALLEGRO_COLOR] structure from CMYK values (cyan, magenta, yellow,
black).

See also: [al_color_cmyk_to_rgb], [al_color_rgb_to_cmyk]


## API: al_color_cmyk_to_rgb

Convert CMYK values to RGB values.

See also: [al_color_cmyk], [al_color_rgb_to_cmyk]


## API: al_color_hsl

Return an [ALLEGRO_COLOR] structure from HSL (hue, saturation, lightness)
values.

Parameters:

* hue - Color hue angle in the range 0..360
* saturation - Color saturation in the range 0..1
* lightness - Color lightness in the range 0..1

See also: [al_color_hsl_to_rgb], [al_color_hsv]


## API: al_color_hsl_to_rgb

Convert values in HSL color model to RGB color model.

Parameters:

* hue - Color hue angle in the range 0..360
* saturation - Color saturation in the range 0..1
* lightness - Color lightness in the range 0..1
* red, green, blue - returned RGB values in the range 0..1

See also: [al_color_rgb_to_hsl], [al_color_hsl], [al_color_hsv_to_rgb]


## API: al_color_hsv

Return an [ALLEGRO_COLOR] structure from HSV (hue, saturation, value)
values.

Parameters:

* hue - Color hue angle in the range 0..360
* saturation - Color saturation in the range 0..1
* value - Color value in the range 0..1

See also: [al_color_hsv_to_rgb], [al_color_hsl]


## API: al_color_hsv_to_rgb

Convert values in HSV color model to RGB color model.

Parameters:

* hue - Color hue angle in the range 0..360
* saturation - Color saturation in the range 0..1
* value - Color value in the range 0..1
* red, green, blue - returned RGB values in the range 0..1

See also: [al_color_rgb_to_hsv], [al_color_hsv], [al_color_hsl_to_rgb]


## API: al_color_html

Interprets an HTML-style hex number (e.g. #00faff) as a color.
The accepted format is the same as [al_color_html_to_rgb].

Returns the interpreted color, or `al_map_rgba(0, 0, 0, 0)` if the string
could not be parsed.

> *Note*: the behaviour on invalid strings is different from Allegro 5.0.x.

See also: [al_color_html_to_rgb], [al_color_rgb_to_html]


## API: al_color_html_to_rgb

Interprets an HTML-style hex number (e.g. #00faff) as a color.
The only accepted formats are "#RRGGBB" and "RRGGBB" where R, G, B are
hexadecimal digits [0-9A-Fa-f].

Returns true on success, false on failure.
On failure all components are set to zero.

> *Note*: the behaviour on invalid strings is different from Allegro 5.0.x.

See also: [al_color_html], [al_color_rgb_to_html]


## API: al_color_rgb_to_html

Create an HTML-style string representation of an [ALLEGRO_COLOR],
e.g. #00faff.

Parameters:

* red, green, blue - The color components in the range 0..1.
* string - A pointer to a buffer of at least 8 bytes, into which the result
  will be written (including the NUL terminator).

Example:

~~~~c
char html[8];
al_color_rgb_to_html(1, 0, 0, html);
~~~~

Now html will contain "#ff0000".

See also: [al_color_html], [al_color_html_to_rgb]


## API: al_color_name

Return an [ALLEGRO_COLOR] with the given name.  If the color is not found then
black is returned.

See [al_color_name_to_rgb] for the list of names.


## API: al_color_name_to_rgb

Parameters:

* name - The (lowercase) name of the color.
* r, g, b - If one of the recognized color names below is passed,
  the corresponding RGB values in the range 0..1 are written.

The 148 recognized names are:

> aliceblue, antiquewhite, aqua, aquamarine, azure, beige, bisque,
black, blanchedalmond, blue, blueviolet, brown, burlywood, cadetblue,
chartreuse, chocolate, coral, cornflowerblue, cornsilk, crimson,
cyan, darkblue, darkcyan, darkgoldenrod, darkgray, darkgreen,
darkkhaki, darkmagenta, darkolivegreen, darkorange, darkorchid,
darkred, darksalmon, darkseagreen, darkslateblue, darkslategray,
darkturquoise, darkviolet, deeppink, deepskyblue, dimgray,
dodgerblue, firebrick, floralwhite, forestgreen, fuchsia, gainsboro,
ghostwhite, goldenrod, gold, gray, green, greenyellow, honeydew,
hotpink, indianred, indigo, ivory, khaki, lavenderblush, lavender,
lawngreen, lemonchiffon, lightblue, lightcoral, lightcyan,
lightgoldenrodyellow, lightgreen, lightgrey, lightpink,
lightsalmon, lightseagreen, lightskyblue, lightslategray,
lightsteelblue, lightyellow, lime, limegreen, linen, magenta, maroon,
mediumaquamarine, mediumblue, mediumorchid, mediumpurple,
mediumseagreen, mediumslateblue, mediumspringgreen, mediumturquoise,
mediumvioletred, midnightblue, mintcream, mistyrose, moccasin, 
avajowhite, navy, oldlace, olive, olivedrab, orange, orangered,
orchid, palegoldenrod, palegreen, paleturquoise, palevioletred,
papayawhip, peachpuff, peru, pink, plum, powderblue, purple,
rebeccapurple, red, rosybrown, royalblue, saddlebrown, salmon,
sandybrown, seagreen, seashell, sienna, silver, skyblue, slateblue,
slategray, snow, springgreen, steelblue, tan, teal, thistle, tomato,
turquoise, violet, wheat, white, whitesmoke, yellow, yellowgreen

They are taken from CSS: <https://www.w3.org/TR/css-color-4/>

Note that these 9 colors have two names and so there are only 139
distinct colors: aqua = cyan, darkgray = darkgrey, darkslategray =
darkslategrey, dimgray = dimgrey, fuchsia = purple, gray = grey,
lightgray = lightgrey, lightslategray = lightslategrey, slategray =
slategrey

Returns:
true if a name from the list above was passed, else false.

See also: [al_color_name]


## API: al_color_rgb_to_cmyk

Each RGB color can be represented in CMYK with a K component of 0
with the following formula:

    C = 1 - R
    M = 1 - G
    Y = 1 - B
    K = 0

This function will instead find the representation with the maximal
value for K and minimal color components.

See also: [al_color_cmyk], [al_color_cmyk_to_rgb]


## API: al_color_rgb_to_hsl

Given an RGB triplet with components in the range 0..1, return
the hue in degrees from 0..360 and saturation and lightness in the
range 0..1.

See also: [al_color_hsl_to_rgb], [al_color_hsl]


## API: al_color_rgb_to_hsv

Given an RGB triplet with components in the range 0..1, return
the hue in degrees from 0..360 and saturation and value in the
range 0..1.

See also: [al_color_hsv_to_rgb], [al_color_hsv]


## API: al_color_rgb_to_name

Given an RGB triplet with components in the range 0..1, find a color
name describing it approximately.

See also: [al_color_name_to_rgb], [al_color_name]


## API: al_color_rgb_to_xyz

Convert RGB values to XYZ color space.

Since: 5.2.3

See also: [al_color_xyz], [al_color_xyz_to_rgb]


## API: al_color_xyz

Return an [ALLEGRO_COLOR] structure from XYZ values. The CIE 1931 XYZ
color space consists of three components in the range 0..1. The Y
component corresponds to luminance and the X and Z components define
the color.

RGB components are always assumed to be in sRGB space.

> *Note:*
>
> The XYZ color space can represent more colors than are
> visible in sRGB and therefore conversion may result in RGB values
> outside of the 0..1 range. You can check for that case with
> [al_is_color_valid].

Since: 5.2.3

See also: [al_color_xyz_to_rgb], [al_color_rgb_to_xyz]


## API: al_color_xyz_to_rgb

Convert XYZ color values to RGB color space.

Since: 5.2.3

See also: [al_color_xyz], [al_color_rgb_to_xyz]


## API: al_color_rgb_to_xyy

Convert RGB values to xyY color space.

Since: 5.2.3

See also: [al_color_xyy], [al_color_xyy_to_rgb]


## API: al_color_xyy

Return an [ALLEGRO_COLOR] structure from xyY values. The Y component
in the xyY color space is the same as the Y in XYZ.

However the x and y values are computed from XYZ like this:

~~~~c
x = X / (X + Y + Z)
y = Y / (X + Y + Z)
~~~~

Since: 5.2.3

See also: [al_color_xyy_to_rgb], [al_color_rgb_to_xyy]


## API: al_color_xyy_to_rgb

Convert xyY color values to RGB color space.

Since: 5.2.3

See also: [al_color_xyy], [al_color_rgb_to_xyy]


## API: al_color_rgb_to_lab

Convert RGB values to L\*a\*b\* color space.

Since: 5.2.3

See also: [al_color_lab], [al_color_lab_to_rgb]


## API: al_color_lab

Return an [ALLEGRO_COLOR] structure from CIE L\*a\*b\* values. The L\*
component corresponds to luminance from 0..1. The a\* and b\* components
are in the range -1..+1.

> *Note:*
>
> The L\*a\*b\* color space can represent more colors than are
> visible in sRGB and therefore conversion may result in RGB values
> outside of the 0..1 range. You can check for that case with
> [al_is_color_valid].

> *Note:*
>
> In some literature the range of L* is 0 to 100 and a* and b* are from
> -100 to +100. In that case divide all components by 100 before passing
> them to this function.

Since: 5.2.3

See also: [al_color_lab_to_rgb], [al_color_rgb_to_lab]


## API: al_color_lab_to_rgb

Convert CIE L\*a\*b\* color values to RGB color space.

Since: 5.2.3

See also: [al_color_lab], [al_color_rgb_to_lab]


## API: al_color_rgb_to_lch

Convert RGB values to CIE LCH color space. 

Since: 5.2.3

See also: [al_color_lch], [al_color_lch_to_rgb]


## API: al_color_lch

Return an [ALLEGRO_COLOR] structure from CIE LCH values. LCH colors are
very similar to HSL, with the same meaning of L and H and C
corresponding to S. However LCH is more visually uniform. Furthermore,
this function expects the angle for H in radians and not in degree.

The CIE LCH color space is a cylindrical representation of the L\*a\*b\*
color space. The L component is the same and C and H are computed like
this:

~~~~c
C = sqrt(a * a + b * b)
H = atan2(b, a)
~~~~

Since: 5.2.3

See also: [al_color_lch_to_rgb], [al_color_rgb_to_lch]


## API: al_color_lch_to_rgb

Convert CIE LCH color values to RGB color space.

Since: 5.2.3

See also: [al_color_lch], [al_color_rgb_to_lch]


## API: al_color_distance_ciede2000_lab

This function computes the CIEDE2000 color difference between two
RGB colors. This is a visually uniform color difference, unlike for
example the RGB distance.

When using the RGB distance (Euklidean distance between two RGB
triplets) there can be color pairs with the same distance, where the
colors of one pair appear to be almost the same color, while the colors
of the other pair look quite different. This is improved by using the
L\*a\*b\* color space which was designed with perceptual uniformity in
mind. However it still is not completely uniform. The CIEDE2000
formula contains some additional transformations to fix that.

The returned color distance is roughly in the range 0 (identical
color) to 1 (completely different color) - but values greater than one
are possible.

> Note: This function uses [al_color_lab] internally which
> defines the L component to be in the range 0..1 (and not 0..100 as is
> sometimes seen).

Since: 5.2.3

## API: al_color_rgb_to_yuv

Convert RGB values to YUV color space.

See also: [al_color_yuv], [al_color_yuv_to_rgb]


## API: al_color_yuv

Return an [ALLEGRO_COLOR] structure from YUV values.

See also: [al_color_yuv_to_rgb], [al_color_rgb_to_yuv]


## API: al_color_yuv_to_rgb

Convert YUV color values to RGB color space.

See also: [al_color_yuv], [al_color_rgb_to_yuv]


## API: al_get_allegro_color_version

Returns the (compiled) version of the addon, in the same format as
[al_get_allegro_version].


## API: al_is_color_valid

Checks if all components of the color are between 0 and 1. Some of the
color conversions in this addon support color spaces with more colors
than can be represented in sRGB and when converted to RGB will result
in invalid color components outside the 0..1 range.

Since: 5.2.3
