Trimming/Rotating JPEG files

When I trim a jpeg file, will the trimmed (remaining) portion retain the same image quality as the original?

My thinking is that since the trimmed portion will be saved as a separated jpeg file, this introduces jpeg compression which in turn might result in loss of image quality to a certain degree. If I subsequently print the trimmed portion to its full size, I might not be able to see the same sharpness or shadow details as would the original. Am I correct?

I assume the same holds true when I do a jpeg file rotation. If I do a rotation followed by some trimming, the resulting quality might even be worse. Correct?

In my experience (mostly jpeg) triming or any change is re saved and some quality is lost....
It is at this point I move to a lossless format such as .psd or .xcf or even a .tiff.....I return to a .jpeg save after completing the work on the photo.....

I do loss-less rotation and croping in my browser (FastStone or XnView) prior to working on the images...some editing software will do auto rotation on opening......

Most of all, I don't worry too much about it......:)

If your camera is so equipped, why not take your shots in RAW format and save them as such.

You can then process these for use and save as jpegs (or TIFF etc if you want to remain in a lossless format).

Some cameras have the ability to save a RAW & jpeg at the same time which can be useful.

However, unless you are creating giant enlargements, as Willgoss says, don't worry about it too much.

Some programs like FastStone Viewer and IrfanView offer a lossless jpg rotation. Saving a jpg as a jpg is throwing data away, simple solution: save as .tif. If you must use .jpg then save at 100% to minimize data loss. You'll be hard pressed to see the difference, but the file size may show it. When preparing jpg files for the web a program like Advanced Jpg Compressor is helpful, giving a lot of control over what gets thrown away in the course of optimization, resulting in better looking files with much smaller file sizes than Photoshop can produce.

In FastStone you can crop without loss less and it saves as a jpg with .cr added to the name....

I have tested it with 12 crops in a row, overwriting the previous....I can see no loss compared with the original jpg image.....

I have also tested repeated saves in the program at 97%, without making any change and I find little loss over 5 saves....

It's when you start making changes to the image that the image changes with accomping loss...

Thanks for the info. By FastStone are you referring to FastStone Photo Resizer, or FastStone Image Viewer? Both of them seem to have the rotate/crop functions... I'm not sure which one has the lossless crop.

I am using the FastStone Image Viewer as I also use it as my Browser for all of my Graphics programs....it has lots of other features such as email, different screen captures, resizing......

XnView is also good with more file type options...but beyond that, I like FastStone better...