Provided by: libpdl-graphics-colorspace-perl_0.206-1_amd64 
NAME
PDL::Graphics::ColorSpace - colour-space conversions for PDL
SYNOPSIS
use PDL::LiteF;
use PDL::IO::Pic;
use PDL::Graphics::ColorSpace;
my $image_rgb = PDL->rpic('photo.jpg') if PDL->rpiccan('JPEG');
# convert RGB value from [0,255] to [0,1]
$image_rgb = $image_rgb->double / 255;
my $image_xyz = $image_rgb->rgb_to_xyz( 'sRGB' );
Or
my $image_xyz = rgb_to_xyz( $image_rgb, 'sRGB' );
DESCRIPTION
Does image color space conversions such as RGB to XYZ and Lab to LCH. Derived from Graphics::ColorObject
(Izvorski & Reibenschuh, 2005) but since it's implemented in C and PDL, it runs *much* faster.
Often the conversion will return out-of-gamut values. Retaining out-of-gamut values allows chained
conversions to be lossless and reverse conversions to produce the original values. You can clip the
values to be within-gamut if necessary. Please check the specific color space for the gamut range.
COLOR SPACES
RGB
An RGB color space is any additive color space based on the RGB color model. A particular RGB color space
is defined by the three chromaticities of the red, green, and blue additive primaries, and can produce
any chromaticity that is the triangle defined by those primary colors. The complete specification of an
RGB color space also requires a white point chromaticity and a gamma correction curve.
For more info on the RGB color space, see <http://en.wikipedia.org/wiki/RGB_color_space>.
This module expects and produces RGB values normalized to be in the range of [0,1]. If you have / need
integer value between [0,255], divide or multiply the values by 255.
CMYK
CMYK refers to the four inks used in some color printing: cyan, magenta, yellow, and key (black). The
CMYK model works by partially or entirely masking colors on a lighter, usually white, background. The ink
reduces the light that would otherwise be reflected. Such a model is called subtractive because inks
"subtract" brightness from white.
In additive color models such as RGB, white is the "additive" combination of all primary colored lights,
while black is the absence of light. In the CMYK model, it is the opposite: white is the natural color of
the paper or other background, while black results from a full combination of colored inks. To save money
on ink, and to produce deeper black tones, unsaturated and dark colors are produced by using black ink
instead of the combination of cyan, magenta and yellow.
For more info, see <http://en.wikipedia.org/wiki/CMYK_color_model>.
HSL
Hue, Saturation and Luminance (or brightness).
The HSL color space defines colors more naturally: Hue specifies the base color, the other two values
then let you specify the saturation of that color and how bright the color should be.
Hue is specified here as degrees ranging from 0 to 360. There are 6 base colors:
0 red
60 yellow
120 green
180 cyan
240 blue
300 magenta
360 red
Saturation specifies the distance from the middle of the color wheel. So a saturation value of 0 (0%)
means "center of the wheel", i.e. a grey value, whereas a saturation value of 1 (100%) means "at the
border of the wheel", where the color is fully saturated.
Luminance describes how "bright" the color is. 0 (0%) means 0 brightness and the color is black. 1 (100%)
means maximum brightness and the color is white.
For more info, see <http://www.chaospro.de/documentation/html/paletteeditor/colorspace_hsl.htm>.
XYZ and xyY
The CIE XYZ color space was derived the CIE RGB color space. XYZ are three hypothetical primaries. Y
means brightness, Z is quasi-equal to blue stimulation, and X is a mix which looks like red sensitivity
curve of cones. All visible colors can be represented by using only positive values of X, Y, and Z. The
main advantage of the CIE XYZ space (and any color space based on it) is that this space is completely
device-independent.
For more info, see <http://en.wikipedia.org/wiki/CIE_1931_color_space>.
Lab
A Lab color space is a color-opponent space with dimension L for lightness and a and b for the color-
opponent dimensions, based on nonlinearly compressed CIE XYZ color space coordinates. It's derived from
the "master" space CIE 1931 XYZ color space but is more perceptually uniform than XYZ. The Lab space is
relative to the white point of the XYZ data they were converted from. Lab values do not define absolute
colors unless the white point is also specified.
For more info, see <http://en.wikipedia.org/wiki/Lab_color_space>.
LCH
This is possibly a little easier to comprehend than the Lab colour space, with which it shares several
features. It is more correctly known as L*C*H*. Essentially it is in the form of a sphere. There are
three axes; L* and C* and H°.
The L* axis represents Lightness. This is vertical; from 0, which has no lightness (i.e. absolute black),
at the bottom; through 50 in the middle, to 100 which is maximum lightness (i.e. absolute white) at the
top.
The C* axis represents Chroma or "saturation". This ranges from 0 at the centre of the circle, which is
completely unsaturated (i.e. a neutral grey, black or white) to 100 or more at the edge of the circle for
very high Chroma (saturation) or "colour purity".
If we take a horizontal slice through the centre, we see a coloured circle. Around the edge of the circle
we see every possible saturated colour, or Hue. This circular axis is known as H° for Hue. The units are
in the form of degrees° (or angles), ranging from 0 (red) through 90 (yellow), 180 (green), 270 (blue)
and back to 0.
For more info, see <http://www.colourphil.co.uk/lab_lch_colour_space.html>.
OPTIONS
Some conversions require specifying the RGB space which includes gamma curve and white point definitions.
Supported RGB spaces include (aliases in square brackets):
Adobe RGB (1998) [Adobe]
Apple RGB [Apple]
BestRGB
Beta RGB
BruceRGB
CIE
ColorMatch
DonRGB4
ECI
Ekta Space PS5
NTSC [601] [CIE Rec 601]
PAL/SECAM [PAL] [CIE ITU]
ProPhoto
SMPTE-C [SMPTE]
WideGamut
sRGB [709] [CIE Rec 709]
lsRGB
You can also add custom RGB space definitions via the function add_rgb_space. Alternatively, as of 0.202
you can directly supply the function with a hash-ref in the same format.
CONVERSIONS
Some conversions, if not already included as functions, can be achieved by chaining existing functions.
For example, LCH to HSV conversion can be achieved by chaining lch_to_rgb and rgb_to_hsv:
my $hsv = rgb_to_hsv( lch_to_rgb( $lch, 'sRGB' ), 'sRGB' );
To generate a local diagram of what conversions are available between formats, using GraphViz, you can
use this script:
use blib;
use PDL::Graphics::ColorSpace;
print "digraph {\n";
print join(' -> ', split /_to_/), "\n"
for grep !/^_/ && /_to_/, @PDL::Graphics::ColorSpace::EXPORT_OK;
print "}\n";
# then:
perl scriptname >d.dot; dot -Tsvg d.dot >d.svg; display d.svg
(As of 0.202, this is everything to and from "rgb", plus "xyz" <-> "lab" <-> "lch")
FUNCTIONS
rgb_to_cmyk
Signature: (rgb(c=3); [o]cmyk(d=4))
Converts an RGB color triple to an CMYK color quadruple.
The first dimension of the ndarrays holding the rgb values must be size 3, i.e. the dimensions must look
like (3, m, n, ...). The first dimension of the ndarrays holding the cmyk values must be size 4.
Usage:
my $cmyk = rgb_to_cmyk( $rgb );
If "rgb_to_cmyk" encounters a bad value in any of the R, G, or B values the output ndarray will be marked
as bad and the associated C, M, Y, and K values will all be marked as bad.
cmyk_to_rgb
Signature: (cmyk(d=4); [o]rgb(c=3))
Converts an CMYK color quadruple to an RGB color triple
The first dimension of the ndarrays holding the cmyk values must be size 4, i.e. the dimensions must look
like (4, m, n, ...). The first dimension of the ndarray holding the rgb values must be 3.
Usage:
my $rgb = cmyk_to_rgb( $cmyk );
If "cmyk_to_rgb" encounters a bad value in any of the C, M, Y, or K quantities, the output ndarray will
be marked as bad and the associated R, G, and B color values will all be marked as bad.
rgb_to_hsl
Signature: (rgb(c=3); [o]hsl(c=3))
Converts an RGB color triple to an HSL color triple.
The first dimension of the ndarrays holding the hsl and rgb values must be size 3, i.e. the dimensions
must look like (3, m, n, ...).
Usage:
my $hsl = rgb_to_hsl( $rgb );
If "rgb_to_hsl" encounters a bad value in any of the R, G, or B values the output ndarray will be marked
as bad and the associated H, S, and L values will all be marked as bad.
hsl_to_rgb
Signature: (hsl(c=3); [o]rgb(c=3))
Converts an HSL color triple to an RGB color triple
The first dimension of the ndarrays holding the hsl and rgb values must be size 3, i.e. the dimensions
must look like (3, m, n, ...).
Usage:
my $rgb = hsl_to_rgb( $hsl );
If "hsl_to_rgb" encounters a bad value in any of the H, S, or V quantities, the output ndarray will be
marked as bad and the associated R, G, and B color values will all be marked as bad.
rgb_to_hsv
Signature: (rgb(c=3); [o]hsv(c=3))
Converts an RGB color triple to an HSV color triple.
The first dimension of the ndarrays holding the hsv and rgb values must be size 3, i.e. the dimensions
must look like (3, m, n, ...).
Usage:
my $hsv = rgb_to_hsv( $rgb );
If "rgb_to_hsv" encounters a bad value in any of the R, G, or B values the output ndarray will be marked
as bad and the associated H, S, and V values will all be marked as bad.
hsv_to_rgb
Signature: (hsv(c=3); [o]rgb(c=3))
Converts an HSV color triple to an RGB color triple
The first dimension of the ndarrays holding the hsv and rgb values must be size 3, i.e. the dimensions
must look like (3, m, n, ...).
Usage:
my $rgb = hsv_to_rgb( $hsv );
If "hsv_to_rgb" encounters a bad value in any of the H, S, or V quantities, the output ndarray will be
marked as bad and the associated R, G, and B color values will all be marked as bad.
xyY_to_xyz
Signature: (xyY(c=3); [o]xyz(c=3))
Internal function for white point calculation. Use it if you must.
xyY_to_xyz processes bad values. It will set the bad-value flag of all output ndarrays if the flag is
set for any of the input ndarrays.
lab_to_lch
Signature: (lab(c=3); [o]lch(c=3))
Converts an Lab color triple to an LCH color triple.
The first dimension of the ndarrays holding the lab values must be size 3, i.e. the dimensions must look
like (3, m, n, ...).
Usage:
my $lch = lab_to_lch( $lab );
If "lab_to_lch" encounters a bad value in any of the L, a, or b values the output ndarray will be marked
as bad and the associated L, C, and H values will all be marked as bad.
lch_to_lab
Signature: (lch(c=3); [o]lab(c=3))
Converts an LCH color triple to an Lab color triple.
The first dimension of the ndarrays holding the lch values must be size 3, i.e. the dimensions must look
like (3, m, n, ...).
Usage:
my $lab = lch_to_lab( $lch );
If "lch_to_lab" encounters a bad value in any of the L, C, or H values the output ndarray will be marked
as bad and the associated L, a, and b values will all be marked as bad.
rgb_to_linear
Signature: (rgb(c=3); gamma(); [o]out(c=3))
Converts an RGB color triple (presumably with gamma) to an RGB color triple with linear values.
Usage:
my $rgb_linear = rgb_to_linear( $gammaed, 2.2 );
If "rgb_to_linear" encounters a bad value in any of the R, G, or B values the output ndarray will be
marked as bad and the associated R, G, and B values will all be marked as bad.
rgb_from_linear
Signature: (rgb(c=3); gamma(); [o]out(c=3))
Converts an RGB color triple (presumably linear) to an RGB color triple with the specified gamma.
Usage:
my $gammaed = rgb_from_linear( $rgb_linear, 2.2 );
If "rgb_from_linear" encounters a bad value in any of the R, G, or B values the output ndarray will be
marked as bad and the associated R, G, and B values will all be marked as bad.
rgb_to_xyz
Converts an RGB color triple to an XYZ color triple.
The first dimension of the ndarrays holding the rgb values must be size 3, i.e. the dimensions must look
like (3, m, n, ...).
If "rgb_to_xyz" encounters a bad value in any of the R, G, or B values the output ndarray will be marked
as bad and the associated X, Y, and Z values will all be marked as bad.
Usage:
my $xyz = rgb_to_xyz( $rgb, 'sRGB' );
my $xyz = rgb_to_xyz( $rgb, \%rgb_spec );
xyz_to_rgb
Converts an XYZ color triple to an RGB color triple.
The first dimension of the ndarrays holding the xyz and rgb values must be size 3, i.e. the dimensions
must look like (3, m, n, ...).
If "xyz_to_rgb" encounters a bad value in any of the X, Y, or Z values the output ndarray will be marked
as bad and the associated R, G, and B values will all be marked as bad.
Usage:
my $rgb = xyz_to_rgb( $xyz, 'sRGB' );
my $rgb = xyz_to_rgb( $xyz, \%rgb_spec );
xyz_to_lab
Converts an XYZ color triple to an Lab color triple.
The first dimension of the ndarrays holding the xyz values must be size 3, i.e. the dimensions must look
like (3, m, n, ...).
If "xyz_to_lab" encounters a bad value in any of the X, Y, or Z values the output ndarray will be marked
as bad and the associated L, a, and b values will all be marked as bad.
Usage:
my $lab = xyz_to_lab( $xyz, 'sRGB' );
my $lab = xyz_to_lab( $xyz, \%rgb_spec );
lab_to_xyz
Converts an Lab color triple to an XYZ color triple.
The first dimension of the ndarrays holding the lab values must be size 3, i.e. the dimensions must look
like (3, m, n, ...).
If "lab_to_xyz" encounters a bad value in any of the L, a, or b values the output ndarray will be marked
as bad and the associated X, Y, and Z values will all be marked as bad.
Usage:
my $xyz = lab_to_xyz( $lab, 'sRGB' );
my $xyz = lab_to_xyz( $lab, \%rgb_spec );
rgb_to_lch
Converts an RGB color triple to an LCH color triple.
The first dimension of the ndarrays holding the rgb values must be size 3, i.e. the dimensions must look
like (3, m, n, ...).
If "rgb_to_lch" encounters a bad value in any of the R, G, or B values the output ndarray will be marked
as bad and the associated L, C, and H values will all be marked as bad.
Usage:
my $lch = rgb_to_lch( $rgb, 'sRGB' );
my $lch = rgb_to_lch( $rgb, \%rgb_spec );
lch_to_rgb
Converts an LCH color triple to an RGB color triple.
The first dimension of the ndarrays holding the lch values must be size 3, i.e. the dimensions must look
like (3, m, n, ...).
If "lch_to_rgb" encounters a bad value in any of the L, C, or H values the output ndarray will be marked
as bad and the associated R, G, and B values will all be marked as bad.
Usage:
my $rgb = lch_to_rgb( $lch, 'sRGB' );
my $rgb = lch_to_rgb( $lch, \%rgb_spec );
rgb_to_lab
Converts an RGB color triple to an LAB color triple.
The first dimension of the ndarrays holding the rgb values must be size 3, i.e. the dimensions must look
like (3, m, n, ...).
If "rgb_to_lab" encounters a bad value in any of the R, G, or B values the output ndarray will be marked
as bad and the associated L, A, and B values will all be marked as bad.
Usage:
my $lab = rgb_to_lab( $rgb, 'sRGB' );
my $lab = rgb_to_lab( $rgb, \%rgb_spec );
lab_to_rgb
Converts an LAB color triple to an RGB color triple.
The first dimension of the ndarrays holding the lab values must be size 3, i.e. the dimensions must look
like (3, m, n, ...).
If "lab_to_rgb" encounters a bad value in any of the L, A, or B values the output ndarray will be marked
as bad and the associated R, G, and B values will all be marked as bad.
Usage:
my $rgb = lab_to_rgb( $lab, 'sRGB' );
my $rgb = lab_to_rgb( $lab, \%rgb_spec );
add_rgb_space
Supports adding custom RGB space definitions. The "m" and "white_point" can be supplied as PDL ndarrays
if desired. As of 0.202, you don't need to provide an "mstar" since the inverse of the "m" will be
calculated (once) as a default.
Usage:
my %custom_space = (
custom_1 => {
'gamma' => '2.2',
'm' => [
[
'0.467384242424242',
'0.240995',
'0.0219086363636363'
],
[
'0.294454030769231',
'0.683554',
'0.0736135076923076'
],
[
'0.18863',
'0.075452',
'0.993451333333334'
]
],
'white_point' => [
'0.312713',
'0.329016'
],
},
custom_2 => { ... },
);
add_rgb_space( \%custom_space );
my $rgb = lch_to_rgb( $lch, 'custom_1' );
SEE ALSO
Graphics::ColorObject
AUTHOR
~~~~~~~~~~~~ ~~~~~ ~~~~~~~~ ~~~~~ ~~~ `` ><(((">
Copyright (C) 2012 Maggie J. Xiong <maggiexyz+github@gmail.com>
Original work sponsored by Shutterstock, LLC <http://www.shutterstock.com/>
All rights reserved. There is no warranty. You are allowed to redistribute this software / documentation
as described in the file COPYING in the PDL distribution.
perl v5.40.0 2025-01-19 ColorSpace(3pm)