Why does this PHP image conversion method create completely transparent images? - php

Question

I am using the below method to batch convert images to the .webp format (borrowed from here):
public function convertToWebp($file, $compression_quality = 80) {
// check if file exists
if (!file_exists($file)) {
return false;
}
// If output file already exists return path
$output_file = $file . '.webp';
if (file_exists($output_file)) {
return $output_file;
}
$file_type = strtolower(pathinfo($file, PATHINFO_EXTENSION));
if (function_exists('imagewebp')) {
switch ($file_type) {
case 'jpeg':
case 'jpg':
$image = imagecreatefromjpeg($file);
break;
case 'png':
$image = imagecreatefrompng($file);
imagepalettetotruecolor($image);
imagealphablending($image, true);
imagesavealpha($image, true);
break;
case 'gif':
$image = imagecreatefromgif($file);
break;
default:
return false;
}
// Save the image
$result = imagewebp($image, $output_file, $compression_quality);
if (false === $result) {
return false;
}
// Free up memory
imagedestroy($image);
return $output_file;
} elseif (class_exists('Imagick')) {
$image = new Imagick();
$image->readImage($file);
if ($file_type === 'png') {
$image->setImageFormat('webp');
$image->setImageCompressionQuality($compression_quality);
$image->setOption('webp:lossless', 'true');
}
$image->writeImage($output_file);
return $output_file;
}
return false;
}
In the view file:
foreach ($images as $image) {
<img class="img-responsive" src="<?= convertToWebp($image);?>"/>
}
The problem
While most of the images are converted successfully, some are completely transparent.
What is missing?
If the Imagick library does not have support for .webp what's a good workaround?