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YCbCr Color Space

YCbCr separates luminance (brightness) from chrominance (color information). It's widely used in video encoding, digital photography, and image compression formats like JPEG.

Channels​

YCbCr has three channels:

  • y (Luminance): Brightness information, 0.0-100.0
  • cb (Blue-difference chroma): Blue-yellow color information, -128 to 127
  • cr (Red-difference chroma): Red-green color information, -128 to 127

Channel Ranges​

  • Luminance (y): 0.0-100.0 (float)
    • 0.0 = Black
    • 100.0 = White
  • Cb (Blue-difference): -128 to 127 (integer)
    • Negative = More blue
    • Positive = More yellow
    • 0 = Neutral
  • Cr (Red-difference): -128 to 127 (integer)
    • Negative = More green
    • Positive = More red
    • 0 = Neutral

Default Values​

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

Creating YCbCr Colors​

use Negarity\Color\Color;

// Create a YCbCr color
$color = Color::ycbcr(78.5, 100, -100);

// Note: Y is a float, Cb and Cr are integers
$color = Color::ycbcr(50.0, 0, 0);  // Gray

Working with YCbCr Channels​

Getting Channel Values​

$color = Color::ycbcr(78.5, 50, -75);

$y = $color->getY();   // 78.5 (float)
$cb = $color->getCb(); // 50 (int)
$cr = $color->getCr(); // -75 (int)

Checking Channel Existence​

use Negarity\Color\ColorSpace\YCbCr;

YCbCr::hasChannel('y');  // true
YCbCr::hasChannel('cb'); // true
YCbCr::hasChannel('cr'); // true
YCbCr::hasChannel('l');  // false (that's Lab/LCh)

Getting Channel Defaults​

use Negarity\Color\ColorSpace\YCbCr;

YCbCr::getChannelDefaultValue('y');  // 0
YCbCr::getChannelDefaultValue('cb'); // 0
YCbCr::getChannelDefaultValue('cr'); // 0

Getting All Channels​

use Negarity\Color\ColorSpace\YCbCr;

YCbCr::getChannels();  // ['y', 'cb', 'cr']

Validation​

YCbCr validates channel values with different ranges for each channel:

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

try {
    // This will throw InvalidColorValueException
    $color = Color::ycbcr(150.0, 50, -75);  // Y exceeds 100.0
} catch (InvalidColorValueException $e) {
    // Handle error
}

try {
    // This will also throw InvalidColorValueException
    $color = Color::ycbcr(50.0, 200, -75);  // Cb exceeds 127
} catch (InvalidColorValueException $e) {
    // Handle error
}

Understanding YCbCr​

Luminance-Chrominance Separation​

YCbCr separates an image into:

  • Y (Luminance): The brightness/grayscale information
  • Cb and Cr (Chrominance): The color information

This separation is useful because:

  • Human vision is more sensitive to brightness than color
  • Chrominance can be compressed more aggressively
  • Allows for efficient image and video compression

The Cb and Cr Channels​

  • Cb (Blue-difference): Represents the blue-yellow axis
    • Negative values = More blue
    • Positive values = More yellow
  • Cr (Red-difference): Represents the red-green axis
    • Negative values = More green
    • Positive values = More red

Mixed Data Types​

YCbCr is unique in that it uses:

  • Float for Y: Allows for precise luminance values
  • Integer for Cb/Cr: Sufficient precision for chrominance

Use Cases​

  • Video Encoding: MPEG, H.264, H.265 video formats
  • Image Compression: JPEG uses a variant of YCbCr
  • Digital Photography: Many cameras use YCbCr internally
  • Broadcast Television: Standard for TV signal transmission
  • Image Processing: Efficient color manipulation and compression

Color Space Information​

use Negarity\Color\ColorSpace\YCbCr;

YCbCr::getName();  // "ycbcr"
YCbCr::getChannels();  // ['y', 'cb', 'cr']
YCbCr::supportsIlluminant();  // false
YCbCr::supportsObserver();  // false

See Also​