Emailing photos and res size

[SsSsSsSsSnake]

I tried 2 different ways to email myself a photo.
this is using mail on my iMac.
1st one used actual size e.g. 20mb by dragging the photo into mail
2nd way using the attachment icon in mail which was about 450kb

when I got them on my iPad i opened the attachment then saved to photos
the larger 20mb full res one i was asked to dl from the cloud i did auto into photos.

looking at the 2 photos there is no difference discernible,can anyone explain why?

thanks

 

[petersmart]

Because in all photos there is a lot of redundancy which can be used to reduce the filesize without seriously impacting on the image quality - unless you go really silly.

I take it the photos you received were JPEGs?

I use a small program called easy thumbnails to resize my edited pics before uploading them to Flickr and that does exactly the same thing.

It can easily reduce a 12 Mb image to about 1.5 Mb with no discernible difference.
.