Preview inflating file size when cropping images

I have a series of images. They are in JPG format. They show up as occupying ~900kb each. I am trying to trim away the borders of these to clean them and save space in printing.

I am cropping the images in Preview. I select what I want, crop, image is trimmed neatly. Great.

When I save the files, however, the size balloons to roughly 1.8MB each. What the hell? I just REMOVED information by cropping the files... roughly 30% to 50% of the image area is getting cropped out and deleted. They are still .JPG files, same as they were before.

What is increasing the file size? I'm assuming it's some kind of profile data getting tacked on; is this correct? How can I get rid of that extra data? Is there a way to set Preview to not do this?

In the meantime, I have tried PNG lossless compression online (Smush.It) in hopes of stripping down the file size, but could only remove ~100kb from each file.

Please help me. ;_;

When you've finished cropping it in Preview File > Save As... PNG, you should get the best quality and file size.

Okay, I'll try it. You know that PNGs aren't always the best size-to-quality ratio, right? Although the files I'm messing with right now are mostly grey scale, so I'd expect they'd make good candidates for PNGs.

The images I'm working with are of general two types: full color images (photographs the size of a sheet of letter paper, scanned in) and grey scale graphic with text (diagrams, also the size of a letter sheet of paper, scanned in).

the full color photograph will hereafter be called Image1
AND
the grey scale graphic will be called Image2

Image1 begins as the unaltered scan, format JPG, file size = 1.0MB.
Image2 is also an unaltered scan, format JPG, file size = 596kb.

Image1 saved as a PNG becomes... 11.6MB.
Image2 saved as a PNG turns into... 4.7MB.

So... uh, that's not working.

Now let's try it from the intermediate step of the cropped JPG with mysteriously inflated file size:

Image1 with some of the border cropped in Preview was saved as a JPG and became 1.9MB. Saving this file again as a PNG makes it 10.8MB.

Image2 with even more border cropped off was saved as a JPG and became 868kb. Saving this file again as a PNG makes it 3.4MB.

What the hell, Preview? There's got to be some crazy metadata getting thrown in there, or a bunch of profiles or something... the mystery remains. ;_: