Why Hidpi Image Is Larger Than The Original Uploaded Image?

I enabled the HiDPI addon.

I uploaded an Image with 1600px ca580kb

After upload, i got two images.

the image@2.jpg is 580kb but with 800px

the image.jpg is 2.7MB and also 800px

Can someone explain, why the original image now is 2.7MB?

And why it is still 800px?

The HiDPI image will use for iphone and else. But i cant use an 2.7MB image for mobile devices. It is to much datavolume for the customer.

Looks like tbirnseth faced similar problem:

http://forum.cs-cart.com/topic/42705-stumped-huge-files-created-on-image-resize/

If on php 5.6 or greater, make sure fileinfo is compiled into your version of php.