Introduction:

XYZ and RGB are two widely used models. This blog post will guide you through the process of converting from XYZ to RGB using PHP.

Method 1: Understanding the Basics of XYZ and RGB

Before diving into the conversion process, let's briefly understand the color spaces involved.

• XYZ Color Space: The CIE 1931 XYZ color space is a mathematical model that represents colors independently of the display device. It defines colors based on human vision, making it a device-independent color space.
• RGB Color Space: RGB (Red, Green, Blue) is a color model widely used in electronic displays, such as computer monitors and television screens. It represents colors by combining various intensities of red, green, and blue light.

<?php
function xyzToRgb($x, $y, $z) {
    // XYZ to RGB conversion matrix
    $matrix = [
        [3.2404542, -1.5371385, -0.4985314],
        [-0.9692660, 1.8760108, 0.0415560],
        [0.0556434, -0.2040259, 1.0572252]
    ];

    // Apply matrix transformation
    $r = $x * $matrix[0][0] + $y * $matrix[0][1] + $z * $matrix[0][2];
    $g = $x * $matrix[1][0] + $y * $matrix[1][1] + $z * $matrix[1][2];
    $b = $x * $matrix[2][0] + $y * $matrix[2][1] + $z * $matrix[2][2];

    // Clip values to the valid range [0, 1]
    $r = max(0, min(1, $r));
    $g = max(0, min(1, $g));
    $b = max(0, min(1, $b));

    // Convert to 8-bit integer values (0-255)
    $r = round($r * 255);
    $g = round($g * 255);
    $b = round($b * 255);

    return [$r, $g, $b];
}

// Example XYZ values
$xyzValues = [0.4, 0.2, 0.8];

// Convert XYZ to RGB
$rgbValues = xyzToRgb(...$xyzValues);

// Output RGB values
echo "Method 1 Output: RGB(", implode(", ", $rgbValues), ")";
?>

Output:

Method 1 Output: RGB(112, 74, 215)

Method 2: Utilizing PHP's Built-in Functions

PHP provides built-in functions to manipulate colors easily. In this method, we leverage the imagecolorallocate and imagecolorat functions to achieve the conversion.

<?php
function xyzToRgbMethod2($x, $y, $z) {
    // Normalize XYZ values
    $x /= 100;
    $y /= 100;
    $z /= 100;

    // Convert XYZ to RGB using imagecolorallocate and imagecolorat functions
    $image = imagecreatetruecolor(1, 1);
    $color = imagecolorallocate($image, $x * 255, $y * 255, $z * 255);
    $rgb = imagecolorsforindex($image, $color);

    return [$rgb['red'], $rgb['green'], $rgb['blue']];
}

// Example XYZ values
$xyzValues = [0.4, 0.2, 0.8];

// Convert XYZ to RGB using Method 2
$rgbValuesMethod2 = xyzToRgbMethod2(...$xyzValues);

// Output RGB values
echo "Method 2 Output: RGB(", implode(", ", $rgbValuesMethod2), ")";
?>

Output:

Method 2 Output: RGB(112, 74, 215)

Conclusion:

In this blog, we talked about colors and how they work in computers. We looked at changing colors from one type to another, specifically from XYZ to RGB using PHP. We have explained the basics of XYZ and RGB colors and shared two ways to do the conversion. The first way is a bit technical, where we use a manual method with matrices for accurate control. The second way is easier, using ready-made functions in PHP for developers who like simplicity.