image-to-gradient.php

<?php

$file = $argv[1];
$threashold = $argv[2] ?? 5;
// Load image
$image = imagecreatefrompng($file);
if (!$image) {
	exit(2);
}

$width = imagesx($image);
$height = imagesy($image);

echo 'file:'.$file.', '.$width.'px X '.$height.'px'.PHP_EOL;

// Convert RGB values to hex
function rgb2hex(array $c)
{
	$g = $c['green'];
	$b = $c['blue'];
	$r = $c['red'];
	$a = $c['alpha'];
	if ($a > 0) {
		return sprintf('rgba(%d,%d,%d,%d)', $r, $g, $b, $a);
	}
	return sprintf('#%02x%02x%02x', $r, $g, $b);
}

$a = [];
// Get color at left (0,0) and right (width,0) edges
$lc = null;
for ($i = 0; $i < $height; $i++) {
	$color = imagecolorsforindex($image, imagecolorat($image, 0, $i));
	for ($j = 1; $j < $width; $j++) {
		$colorj = imagecolorsforindex($image, imagecolorat($image, $j, $i));
		if (rgb2hex($color) != rgb2hex($colorj)) {
			echo "ERR: " . $j . ',' . $i . ' color differs in row: ' . rgb2hex($color) . ', ' . rgb2hex($colorj) . PHP_EOL;
			exit(1);
		}
	}
	if ($i > 1 && $i < $height - 1) {
		$next = imagecolorsforindex($image, imagecolorat($image, 0, $i + 1));

    $delta = abs($next['red'] - $color['red'] - ($color['red'] - $lc['red'])) +
		abs($next['green'] - $color['green'] - ($color['green'] - $lc['green'])) +
		abs($next['blue'] - $color['blue'] - ($color['blue'] - $lc['blue'])) +
		abs($next['alpha'] - $color['alpha'] - ($color['alpha'] - $lc['alpha']));
		if ($delta < $threashold) {
			echo "\033[0;33m".$delta."\033[0m ";
			
			$lc = $color;
			continue;
		}
		echo "\033[1;31m".$delta."\033[0m ";
	}
	$lc = $color;
	$a[] = rgb2hex($color) . ' ' . round(($i) / ($height - 1) * 100, 1) . '%';
}
echo PHP_EOL;
echo 'background: linear-gradient(to bottom, ' . implode(', ', $a) . ');';
echo PHP_EOL;