when you are loading an image file in an image control, the content is modified to FIT the control...
So if your image control is 800*600, you get an image containing 480000 pixels, EVEN if your original image was 400*300...
So saving that directly to a file will change the content, yes
On top of that (but I haven't tested that part), the image control itself is probably considered RAW format in your case, so even if you reiszed the control to the corrct size for your image before loading the image file in it, it would STILL probably be much bigger with your method, as there is no INPLIED dsauveimagejpg with a percentage of compression.