[PHP] Know the Compression Rate

Hello,

I wrote a PHP script that loads an image, rotates it, and saves it.
My problem is that I want the saving to occur in the same format (jpeg, png, or other) and especially with the same compression rate as the original image.
For the format, it's not an issue; I just need to check the file name.

But is there a way to know the compression rate of a jpeg or png image in PHP?

Thank you,

Xavier

Configuration: Windows XP / Firefox 3.6.9