A coupla points:
- Personally, I would do any changes of this sort to a copy
only, never an original, because they are irreversible! In digital media of any sort, it is trivially easy to lose quality that you can never get back. I always archive originals as they are, keeping multiple copies.
- if you have Microsoft Office on a PC, it comes with the Office Picture Manager that is pretty good for basic image management stuff, including colour corrections, cropping and resizing.
- It's also possible to make a JPEG file take up less space,
without resizing it, by changing the JPEG compression/quality setting. Office Picture Manager can do it in the Export function, and I think IrfanView can too. Typically, JPEG quality from source is around 97%, which is good, but overkill for use on a website or other non-critical application.
Example: I just took a JPEG straight from my camera, at 2.2MB, and played around with the "Save a copy" function in
GIMP. Saved at 100% it took 3MB, but when I lowered the quality to 90%, it took 1.2MB on disk. At 80% it took 700kB, and 500kB at 70% - without resizing it from the original 3000x2000. It was hard to see any difference between the original and 70% when the pictures were viewed side-by-side at 100% zoom - though I bet more experienced "pixel peepers" than me would.
