Yii2 imagecreatefrompng do not work with transparent - php

Question

I use custom model to crop and commpress my image file when uploading. The problem is when upload image/png ... it crop and compress the image, but transparent background replace with black background ... i can not see my mistake ...
here is upload function in controller
$model->imageFiles = UploadedFile::getInstances($model, 'imageFiles[' . $imgKey . ']'); // get the imageFiles
$pic = Yii::getAlias('#frontend/web') . '/product_photos/thumb-270/' . $model->getImageFolderName() . '/' . $fileName; // set the thumb path
$pic2 = Yii::getAlias('#frontend/web') . '/product_photos/' . $model->getImageFolderName() . '/' . $fileName; // set reale image path
$file->saveAs(Yii::getAlias('#frontend/web') . '/product_photos/' . $model->getImageFolderName() . '/' . $fileName);
$image = file_get_contents(Yii::getAlias('#frontend/web') . '/product_photos/' . $model->getImageFolderName() . '/' . $fileName);
file_put_contents($pic, $image);
$model->resizeImg($pic);
if($file->type!='image/png') {
$settings->compress($pic, $pic, 90);
$settings->compress($pic2, $pic2, 90);
}
here is a model function resizeimg:
public function resizeImg($img) {
$sz = getimagesize($img);
$ratio = $sz[0] / $sz[1]; // w/h
$w2 = Yii::$app->params['thumbswidth']; // thumb 1 width
$image = new SimpleImage();
$image->load($img);
$image->resize($w2, round($w2 / $ratio));
$image->save($img);
}
and here is all model SimpleImage:
var $image;
var $image_type;
function load($DATA, $FORMNAME = NULL) {
$image_info = getimagesize($DATA);
$this->image_type = $image_info[2];
if( $this->image_type == IMAGETYPE_JPEG ) {
$this->image = imagecreatefromjpeg($DATA);
} elseif( $this->image_type == IMAGETYPE_GIF ) {
$this->image = imagecreatefromgif($DATA);
} elseif( $this->image_type == IMAGETYPE_PNG ) {
$this->image = imagecreatefrompng($DATA);
}
}
function save($filename, $image_type=IMAGETYPE_JPEG, $compression=100, $permissions=null) {
if( $image_type == IMAGETYPE_JPEG ) {
imagejpeg($this->image,$filename,$compression);
} elseif( $image_type == IMAGETYPE_GIF ) {
imagegif($this->image,$filename);
} elseif( $image_type == IMAGETYPE_PNG ) {
imagepng($this->image,$filename);
}
if( $permissions != null) {
chmod($filename,$permissions);
}
}
function output($image_type=IMAGETYPE_JPEG) {
if( $image_type == IMAGETYPE_JPEG ) {
imagejpeg($this->image);
} elseif( $image_type == IMAGETYPE_GIF ) {
imagegif($this->image);
} elseif( $image_type == IMAGETYPE_PNG ) {
imagepng($this->image);
}
}
function getWidth() {
return imagesx($this->image);
}
function getHeight() {
return imagesy($this->image);
}
function resizeToHeight($height) {
$ratio = $height / $this->getHeight();
$width = $this->getWidth() * $ratio;
$this->resize($width,$height);
}
function resizeToWidth($width) {
$ratio = $width / $this->getWidth();
$height = $this->getheight() * $ratio;
$this->resize($width,$height);
}
function scale($scale) {
$width = $this->getWidth() * $scale/100;
$height = $this->getheight() * $scale/100;
$this->resize($width,$height);
}
function resize($width,$height) {
$new_image = imagecreatetruecolor($width, $height);
imagecopyresampled($new_image, $this->image, 0, 0, 0, 0, $width, $height, $this->getWidth(), $this->getHeight());
imagesavealpha($new_image, true);
$this->image = $new_image;
}