media upload image being processed long time

Hello, i have a problem with the media manager of wordpress.

The upload of a picture is ok and it’s doing quickly. But after the upload there is a treatment and this is writen (in french) something like this “being processed”.
The time of this step is very long and my website become very long to respond until the processing is finish.

I don’t know what’s is doing and why it’s so long. I have deactivate in the option the thumbnail generator and it’s always so long to upload a file due to this long processing time

Any idea of how to optimize this ?

thanks for your help