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XYZ (CIE XYZ) Color Space

XYZ (CIE XYZ) is a device-independent color space based on human color perception. It serves as a fundamental color space in color science and is often used as an intermediate step in color conversions.

Channels​

XYZ has three channels:

  • x: X tristimulus value
  • y: Y tristimulus value (also represents luminance)
  • z: Z tristimulus value

Channel Ranges​

XYZ channels don't have fixed ranges like other color spaces. The values depend on the illuminant and observer used. In Negarity Color:

  • Values are typically in the range 0-100 (scaled for convenience)
  • The Y channel represents luminance and is often used as a reference

Default Values​

All channels default to 0 when not specified, resulting in black (xyz(0, 0, 0)).

CIE Standard Support​

XYZ supports CIE Standard Illuminants and Observers, which are essential for accurate color representation:

  • Illuminants: A, B, C, D50, D55, D65, D75, E, F1-F12
  • Observers: 2° (1931) and 10° (1964)

The default is D65 illuminant with 2° observer, which is standard for most applications.

Creating XYZ Colors​

use Negarity\Color\Color;

// Create an XYZ color with default illuminant/observer
$color = Color::xyz(20, 30, 40);

// Create with specific illuminant and observer
$color = Color::xyz(20, 30, 40,
    CIEIlluminant::D50,
    CIEObserver::TenDegree
);

Working with XYZ Channels​

Getting Channel Values​

$color = Color::xyz(25, 35, 45);

$x = $color->getX();  // 25
$y = $color->getY();  // 35
$z = $color->getZ();  // 45

Checking Channel Existence​

use Negarity\Color\ColorSpace\XYZ;

XYZ::hasChannel('x');  // true
XYZ::hasChannel('y');  // true
XYZ::hasChannel('z');  // true
XYZ::hasChannel('l');  // false (that's Lab)

Getting Channel Defaults​

use Negarity\Color\ColorSpace\XYZ;

XYZ::getChannelDefaultValue('x');  // 0
XYZ::getChannelDefaultValue('y');  // 0
XYZ::getChannelDefaultValue('z');  // 0

Getting All Channels​

use Negarity\Color\ColorSpace\XYZ;

XYZ::getChannels();  // ['x', 'y', 'z']

Checking CIE Support​

use Negarity\Color\ColorSpace\XYZ;

XYZ::supportsIlluminant();  // true
XYZ::supportsObserver();  // true

Validation​

XYZ validates that values are numeric but doesn't enforce strict ranges (as values depend on illuminant/observer):

use Negarity\Color\Color;
use Negarity\Color\Exception\InvalidColorValueException;

try {
    // This will throw InvalidColorValueException
    $color = Color::xyz('invalid', 30, 40);  // Non-numeric value
} catch (InvalidColorValueException $e) {
    // Handle error
}

Understanding XYZ​

Device Independence​

XYZ is device-independent, meaning:

  • It represents colors as humans perceive them, not as devices display them
  • It's based on the CIE 1931 color matching functions
  • It's not tied to any specific display or printing technology

The Y Channel​

The Y channel is special:

  • It represents luminance (brightness)
  • It's normalized so that a perfect white reflector has Y = 100 (for D65)
  • It's used as a reference in many color calculations

Role in Conversions​

XYZ often serves as an intermediate color space:

  • Many color conversions go through XYZ
  • RGB → XYZ → Lab
  • Lab → XYZ → RGB
  • This ensures accurate conversions between different color spaces

Tristimulus Values​

X, Y, and Z are called "tristimulus values" because they represent the three types of color receptors in the human eye (cones).

Use Cases​

  • Color Science: Research and color theory
  • Color Conversions: Intermediate step in color space conversions
  • Color Management: Color profiles and color matching
  • Color Calibration: Device calibration and profiling
  • Color Analysis: Scientific color measurements

Color Space Information​

use Negarity\Color\ColorSpace\XYZ;

XYZ::getName();  // "xyz"
XYZ::getChannels();  // ['x', 'y', 'z']
XYZ::supportsIlluminant();  // true
XYZ::supportsObserver();  // true

See Also​