I've noticed something that surprised me, don't understand it, hoping someone here might be able to explain it...has to do with a dramatic change in the file size after only a single post production tweak, like 'Sharpening'. An example I just tested: JPEG photo file size SOOC to my PC is 4,449 KB. I make a work copy and import it to Lightroom. I simply ran the 'sharpening' slider to its midpoint (75 units). Then exported / saved that work copy back onto my PC. Its file size was cut drastically from 4,449 KB down to 1,889 KB. PS: Same thing happens when I go through the exact same steps using Photobucket's editior...run sharpening slider halfway (50 units in that case) and the resultant file size is hugely reduced to an even lower size...from 4,449 KB way down to a mere 349 KB. In the case of Lightroom, I don't readily notice a physical difference in the size of the displayed image...I do notice a reduced physical size of the image saved back from Photobucket. Soooo...any "post processing reduced file size explanations for dummies" out there?? Two fold question really: "Why does this file size reduction occur"? And "how can this happen yet actually result in improved images"?