Eric Stevens
And I have pointed out that you cannot reverse a change which has not actually been made. Even if it is reversible, you can't reverse something before you have done it.

nospam
the change *has* been made, just not to the pixels themselves.

Eric Stevens
And to what has the change been made?

Sandman
To the pixels. nospam is incorrect here. All LR adjustments are applied to a preview file and saved to disk.

nospam
the changes are rendered on the fly and may be cached to disk (which is the preview file you're talking about). the latter is optional.

Eric Stevens
What do you exactly mean by 'on the fly'.

nospam
it is not a pixel editor.

Eric Stevens
It can't make changes to the pixels and not be a pixel editor. Something is wrong here.