A question about downloading photos from iCloud on PC.

I have a 200GB iCloud plan, and my storage is almost full. I downloaded all of my photos / videos from my iCloud to my PC and then realized that the amount of storage that all my photos / videos took on my PC was 30GB, but on iCloud it was taking up ~185GB of the 200. Im just wondering, are any of my photos / videos not being downloaded? Is it being compressed? I would like to know the reason, thanks 😊