Introduction:

Understanding color spaces is essential in the world of image processing, as different devices and applications use various representations to store and display colors. In this blog post, we will explore the conversion of YCbCr444 to RGB, two common color spaces used in digital imaging. 

YCbCr444 and RGB are two different ways of representing colors, each with its advantages and use cases. YCbCr444 separates luminance (brightness) and chrominance (color information), making it an efficient choice for image and video compression. RGB, on the other hand, is more simple and widely used for display purposes.

Understanding YCbCr444 and RGB

Before we proceed with the conversion, let's briefly understand the YCbCr444 and RGB color spaces.

YCbCr444:

YCbCr444 represents a color in three components:

• Y (Luminance): Represents brightness.
• Cb (Blue Chrominance): Represents the difference between blue and luminance.
• Cr (Red Chrominance): Represents the difference between red and luminance.

RGB:

RGB represents a color in three components:

• Red: The intensity of the red color.
• Green: The intensity of the green color.
• Blue: The intensity of the blue color.

Conversion Formula:

The conversion from YCbCr444 to RGB involves a series of mathematical operations. The formulas for the conversion are as follows:

R = Y + 1.402 × (Cr − 128)

G = Y − 0.344136 × (Cb − 128) − 0.714136 × (Cr − 128)

B = Y + 1.772 × (Cb − 128)

PHP Implementation

Now, let's implement the YCbCr444 to RGB conversion in PHP:

<?php

function ycbcr444_to_rgb($y, $cb, $cr) {
    $r = $y + 1.402 * ($cr - 128);
    $g = $y - 0.344136 * ($cb - 128) - 0.714136 * ($cr - 128);
    $b = $y + 1.772 * ($cb - 128);

    // Clamp values to the valid range [0, 255]
    $r = max(0, min(255, $r));
    $g = max(0, min(255, $g));
    $b = max(0, min(255, $b));

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

// Example usage
$y = 150;
$cb = 120;
$cr = 170;

$rgb = ycbcr444_to_rgb($y, $cb, $cr);

// Output the result
echo "RGB: (R={$rgb[0]}, G={$rgb[1]}, B={$rgb[2]})";

Output:

RGB: (R=178.808, G=149.356, B=232.196)

In the example above, we have an input color in YCbCr444 format with luminance Y = 150, blue chrominance Cb = 120, and red chrominance Cr = 170. The PHP function ycbcr444_to_rgb is used to perform the conversion, and the resulting RGB values are then outputted.

This output indicates that the corresponding RGB values are approximately R = 178.808,  G = 149.356, and  B = 232.196. These values are then clamped to the valid range [0, 255] to ensure they fall within the acceptable color intensity range.

Conclusion:

In this blog, we have explored the conversion from YCbCr444 to RGB using PHP, providing code snippets and explanations for each step. We covered the formulas involved, implemented the conversion in PHP, and showcased an example with an output.