Why do jpeg's cause file size to increase significantly?

[B_C_E_75]

I just created several sets of 2 sided business cards. One side was a full color image, and the other was all of the business info with a small logo and solid black background. All objects were vector except for the full color image. The image was a jpeg and saved to the correct card size with bleed. All text was outlined. 

Full color jpeg image file size- 1.64 MB

Business card file size with jpeg embedded- 32.48 MB

(Adobe pdf settings- high quality print, preserve Illustrator editing capabilities, show trim marks, no compression.)

Ok, something isn't right here? Final file size is HUGE! I check everything. No objects hiding outside the art board, nothing hiding behind something else, only the things that should be there. Re-save and no change in file size. 

I decide to check the jpeg but there is nothing unusual. So I save it as a png to see what happens. 

Full color png image file size- 1.21 MB

Business card file size with png embedded- 5.31 MB ( a reduction of 27 MB!?)

This seems much more realistic. I'm curious as to why the file size with the embedded jpeg was so massive? Without the image embedded, the file size was about 2.5 MB. Something seems messed up with the way Illustrator handles embedded jpegs.  

[Monika Gause · Accepted solution]

Illustrator takes away any kind of compression when embedding a pixel file. On top of that the image will again be embedded in the PDF part of the AI file.

[B_C_E_75]

That doesn't make any sense. The jpeg image file is saved at the size it is. It's always going to be 1.64 MB. That's how it was saved out of photoshop. Those pixels are gone. The original tiff file I saved it from was only 6.44 MB. How is Illustrator undoing any compression? It can't add what's not there. What aren't other pixel files causing the file size to skyrocket?  Saving the same card file with an uncompressed tiff of the same image, saved to the same dimensions, creates a file that is 5.50 MB. How is it that Illustrator is adding 27 MB when there is nothing in the file that remotely adds up to that amount?  

I'm not trying to be argumentative, it's just that I'm not understanding how this is possible.  

[Monika Gause]

JPEG files always have compression added. You might want to read about how that works in the Wikipedia.

[B_C_E_75]

Ah, I see how this is going to go. 

Thanks. 

[Larry G. Schneider]

What happens if you resave the original and replace the existing one with the new version? If you just do a serial save of the original, then any test images you might have used could still be in the unused portions of the original.