It's very inefficient to compress all my site's images in Google's preferred compresion by running webpage after webpage in Google GPI, downloading all images and upload one by one to my CMS image directory.
I would prefer doing so only if no one outside Google know what compression mechanism they use (their compression mechanism is most likely not the one used by tinyPNG).
What image compressor Google Pagespeed Insights uses?
I ask since I thought just to simplify everything by downloading all images to my PC, compress them that way, and thus saving all stages of the GPI valuable-but-sisyphic process.
If it's only a matter of compression percentages, please note the minimal percentage needed to "satisfy" GPI.
If any manipulation by ImageMagick is the efficient way to go, please remind it in your answer.
Why I believe this is not a duplicate:
Here's why I believe this is not a duplicate and should be untagged as such:
The question "Google Pagespeed: New image compression rules?" that appears as such asking about changing of the algorithm in a specific time and place. It is not the same as "What is the compressor used", not by means of question theme or by means of my aim to bring more people to WM SE from Google searched regarding my specific question. Please remove duplication notification.