Why does the transparent background fill incorrectly when converting png to jpg?

Question

Yii

Good afternoon.
When uploading a png image to the site, you need to convert it to jpg to reduce the volume. The site runs on Yii and for this task I use this class (GD is used internally).
I encountered strange behavior of the program when converting images to a transparent background. Usually a transparent background is filled with black, but sometimes there are files that have a torn black stroke around the main object in the photo, and then everything is white. This problem does not occur with all files.
Here's an example of an image that converts fine (first a png, then a jpg result):

490Kb

But this is processed with an error:

525Kb

To convert I use the following code:

$h = new СImageHandler();
$h->load('source.png')->save('res.jpg', $h::IMG_JPEG, 90);

Tell me why this can happen? And how can you fight it?

Answer 1

It's all about saving png in some editors www.artlebedev.ru/tools/technogrette/img/png-3 Try gluing translucent images with a homogeneous background before saving to jpg.

Answer 2

GD is a strange thing. Try php5-imagick. It works faster, more stable and you need to write very little code with it.