Sandman
Well, we all know that YOU rarely have the first clue about what you're talking about, so I have no problem understanding why you're here supporting ignorant Floyd.

Eric Stevens
Floyd's usage is strictly in accordance with http://en.wikipedia.org/wiki/Reversible_process_%28thermodynamics%29

Sandman
Great input, if the topic had been about thermodynamics.

Eric Stevens
The article is about thermodynamics. The concepts and the mathematics and the concept of entropy apply to a number of topics including information processing which, in turn, includes image processing.

as it applies information theory. If you think there is no room for reversible processes in information theory see http://tinyurl.com/otp5pug

Sandman
Why can't you read?

1. Floyd thinks that HPS + JPG compression can be reversed. It can not.

Eric Stevens
He never claimed that the JPG can be reversed.

As I have already written, he said that the original image can be recovered after sharpening by HPS even after the image has been saved as a JPG.

Sandman
2. Floyd thinks that a non-destructive workflow is not a reversible process, it is.

Eric Stevens
It's not a reversible process in the way that he used the term.

You previously quoted from a dictionary. Here is what the New Shorter Oxford English Dictionary says of this particular usage of 'reversible':

"2 Physics. Of a change or process: that is capable of complete and detailed reversal; spec designating or undergoing an ideal change in which a system is thermodynamic equilibrium at all times."

As nospam has so often told us, Lightroom (and other software using side car files)

do not actually change the file being edited until it is in the process of being exported.

In most case, all you see on the screen is a simplified simulacrum of what the edited file will look like, when the editing instructions are executed.

Once you export the file - that's it. You cannot reverse the changes.

All you can do is edit the original all over again but this time slightly differently.

Now it's interesting that Lightroom does incorporate something a little bit like the reversible process that Floyd was talking about but neither nospam or Savageduck seem to realise the fact. See http://tinyurl.com/p5sus42 From blur to sharpness on the one slider. But this is not actually a reversible process: it's a change in the instruction to the final edit which will only be executed when the image is exported.

I do not know the type of sharpening used by Lightroom or whether or not it is truly reversible.

Sandman
Just the plain facts.

Eric Stevens
I'm afraid they are not as plain or as straightforward as you would like to have them.