Today’s Question: In Lightroom if you edit a raw file and save as JPEG I understand the edits are nondestructive to the original raw file. If you then re-edit the JPEG, are the new edits destructive to the JPEG file?
Tim’s Quick Answer: All of the adjustments in the Develop module in Lightroom are non-destructive to the source image file you are currently working on. That includes JPEG images (among other supported file formats) in addition to raw captures.
More Detail: When you apply an adjustment to an image in Lightroom’s Develop module, the changes you apply aren’t actually altering the source image file on your hard drive. Instead, your adjustment settings are essentially metadata updates stored in the Lightroom catalog. This approach ensures Lightroom will be non-destructive to the information in your source images.
When you export an image, you are creating a new file and the adjustments you applied will be incorporated into the pixel values for that image. So, for example, if you export a JPEG image based on a raw capture you’ve adjusted in Lightroom, the source raw file remains unchanged, but the JPEG will reflect the adjustments you applied.
If you import that JPEG image into your Lightroom catalog, you can of course apply new adjustments to that image. Those adjustments will still be non-destructive, meaning the source JPEG image file on your hard drive won’t be altered based on the new adjustments you applied. Of course, if you create a new JPEG based on the existing JPEG using the Export feature, the adjustments will be incorporated into the pixel values for that new JPEG version of the image.
So, in a way, you can think of the adjustments in Lightroom as always being only metadata updates that are non-destructive to the source image. However, exporting a new copy will cause the adjustments to be incorporated into the pixel values for the new image file created as part of that process.