Prestashop image resize - loss of quality - php

Question

I'm using the newest version of Prestashop (1.6.1.5), and I've got some problems with quality of product images.
While resizing (creating thumbnails like large_default, home_default etc) grey stripes appears on destination image.
I followed prestashop code and noticed that it happens after imagecopyresized() function, I tried to replace it with imagecopyresampled() but it doesn't help much.
Here is a link to the original image http://postimg.org/image/ib42bh81t, and here is a link to resized one (the one with grey stripes) http://postimg.org/image/i3tpda7sx
Prestashop resize() method:
public static function resize($src_file, $dst_file, $dst_width = null, $dst_height = null, $file_type = 'jpg',
$force_type = false, &$error = 0, &$tgt_width = null, &$tgt_height = null, $quality = 5,
&$src_width = null, &$src_height = null)
{
if (PHP_VERSION_ID < 50300) {
clearstatcache();
} else {
clearstatcache(true, $src_file);
}
if (!file_exists($src_file) || !filesize($src_file)) {
return !($error = self::ERROR_FILE_NOT_EXIST);
}
list($tmp_width, $tmp_height, $type) = getimagesize($src_file);
$rotate = 0;
if (function_exists('exif_read_data') && function_exists('mb_strtolower')) {
$exif = #exif_read_data($src_file);
if ($exif && isset($exif['Orientation'])) {
switch ($exif['Orientation']) {
case 3:
$src_width = $tmp_width;
$src_height = $tmp_height;
$rotate = 180;
break;
case 6:
$src_width = $tmp_height;
$src_height = $tmp_width;
$rotate = -90;
break;
case 8:
$src_width = $tmp_height;
$src_height = $tmp_width;
$rotate = 90;
break;
default:
$src_width = $tmp_width;
$src_height = $tmp_height;
}
} else {
$src_width = $tmp_width;
$src_height = $tmp_height;
}
} else {
$src_width = $tmp_width;
$src_height = $tmp_height;
}
// If PS_IMAGE_QUALITY is activated, the generated image will be a PNG with .jpg as a file extension.
// This allow for higher quality and for transparency. JPG source files will also benefit from a higher quality
// because JPG reencoding by GD, even with max quality setting, degrades the image.
if (Configuration::get('PS_IMAGE_QUALITY') == 'png_all'
|| (Configuration::get('PS_IMAGE_QUALITY') == 'png' && $type == IMAGETYPE_PNG) && !$force_type) {
$file_type = 'png';
}
if (!$src_width) {
return !($error = self::ERROR_FILE_WIDTH);
}
if (!$dst_width) {
$dst_width = $src_width;
}
if (!$dst_height) {
$dst_height = $src_height;
}
$width_diff = $dst_width / $src_width;
$height_diff = $dst_height / $src_height;
$ps_image_generation_method = Configuration::get('PS_IMAGE_GENERATION_METHOD');
if ($width_diff > 1 && $height_diff > 1) {
$next_width = $src_width;
$next_height = $src_height;
} else {
if ($ps_image_generation_method == 2 || (!$ps_image_generation_method && $width_diff > $height_diff)) {
$next_height = $dst_height;
$next_width = round(($src_width * $next_height) / $src_height);
$dst_width = (int)(!$ps_image_generation_method ? $dst_width : $next_width);
} else {
$next_width = $dst_width;
$next_height = round($src_height * $dst_width / $src_width);
$dst_height = (int)(!$ps_image_generation_method ? $dst_height : $next_height);
}
}
if (!ImageManager::checkImageMemoryLimit($src_file)) {
return !($error = self::ERROR_MEMORY_LIMIT);
}
$tgt_width = $dst_width;
$tgt_height = $dst_height;
$dest_image = imagecreatetruecolor($dst_width, $dst_height);
// If image is a PNG and the output is PNG, fill with transparency. Else fill with white background.
if ($file_type == 'png' && $type == IMAGETYPE_PNG) {
imagealphablending($dest_image, false);
imagesavealpha($dest_image, true);
$transparent = imagecolorallocatealpha($dest_image, 255, 255, 255, 127);
imagefilledrectangle($dest_image, 0, 0, $dst_width, $dst_height, $transparent);
} else {
$white = imagecolorallocate($dest_image, 255, 255, 255);
imagefilledrectangle($dest_image, 0, 0, $dst_width, $dst_height, $white);
}
$src_image = ImageManager::create($type, $src_file);
if ($rotate) {
$src_image = imagerotate($src_image, $rotate, 0);
}
if ($dst_width >= $src_width && $dst_height >= $src_height) {
imagecopyresized($dest_image, $src_image, (int)(($dst_width - $next_width) / 2), (int)(($dst_height - $next_height) / 2), 0, 0, $next_width, $next_height, $src_width, $src_height);
} else {
ImageManager::imagecopyresampled($dest_image, $src_image, (int)(($dst_width - $next_width) / 2), (int)(($dst_height - $next_height) / 2), 0, 0, $next_width, $next_height, $src_width, $src_height, $quality);
}
$write_file = ImageManager::write($file_type, $dest_image, $dst_file);
#imagedestroy($src_image);
return $write_file;
}
I also tried to change quality parameter to 100 or even changed image format to PNG in prestashop - no changes.
What else can I change to fix this quality issues? Any ideas?