One thing to note when using this add-on is the online services like Optimus.io and Imagify.io are pretty much worthless if you are trying to bulk resize all of the images that have already been uploaded to your websites. Those services have like a 5MB limit for each request. It will bottleneck and stop when trying to do a mass bulk conversion. Kraken is the only one that is half way decent in that regard and they have a much larger 32MB limit. I resized all of my images with Kraken, but I had to go in there and keep manually forcing the queue list log to finish until it was fully completed. You will never even get that far using Optimus.io and Imagify.io. Even Ewww.io has the 5MB limit. There is the one bug I found with Ewww.io that has not yet been corrected, but he has already acknowledged that one is real.
I think Kraken.io now is also doing png files so that’s the one I’m am using and without any problems for normal site image upload traffic. I do want to try Ewww.io again though after he corrects the bug, but forget using the other two for bulk conversions. It’s a waste of time. Even Ewww.io will probably bottleneck and stop too when doing mass resize conversions.
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