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.

Sandman
Incorrect.

Eric Stevens
No, quite correct. See, for example: http://tinyurl.com/mbrhs3e

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.

Sandman
Yes, he did. His example included JPG compression and the recieving end being able to reverse a process that took place before the JPG compression.

Eric Stevens
I've just explained that in another article.

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
Which is incorrect.

Eric Stevens
Yes, it should be that the original sharpening can be recovered.

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.

Sandman
I don't care how you think he "used" the term. A non-destructive workflow is a reversible process in every sense of the term.

Eric Stevens
I *know* how he used the term and I have already explained in detail. A non-destructive work flow is not a fully reversible process.

Say I have a bomb, and cause it to explode. If I then with superhuman speed capture all the escaping gases and stuff them back into the ruptured casing, and then slam the casing shut, I might be said to have fully reversed the process. (In fact, that would not be correct in thermodynamic terms).

Say I have another bomb and after I have exploded the first bomb I put the second bomb in it's place. It might now look as if the first bomb had never explodedbut I have not reversed the changes to the first bomb: I have merely substituted for it.

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

Sandman
My quote was *from* Oxford.

Eric Stevens
Then you should have found the part I just quoted.

"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."

Sandman
Funny how you had to ignore the part of the Oxford dictionary that wasn't about physics - which has nothing to do with image processing - and was specifically about "of the effects of a process or condition" which is exactly what we're talking about:

(of the effects of a process or condition) capable of being reversed so that the previous state or situation is restored

Eric Stevens
You will see why this does not apply to the LR situation when you consider my example of the bombs.

Sandman
Don't quote dictionaries if you don't know which part of them to quote.

Eric Stevens
But I do know which part to quote.

I quoted the bit that I did to show Floyd was correct in his usage.

That doesn't mean that it is the only possible meaning for the term reversible but, in this case, the use of the other meanings is incorrect.

Sandman
Incorrect. The file is *never* changed. Lightroom has a preview file that is constantly being updated to reflect the adjustment changes you make. This is a JPG file that resides on your hard drive at all times. For every single adjustment you make in Lightroom, it creates a current-state preview file on disk. The original file is never touched.

Eric Stevens
True, but it is neither of these which is 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.

Sandman
Incorrect, what you see on the screen is exactly what the exported file - if you even export it - will look like. It's not simplified, and it's not a representation of something else.

Eric Stevens
How can it be identical, how can it contain the same amount of image information if it is a much smaller file.

I've already commented mine are generally between 50% and 20% of the size of the original?

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

Sandman
Incorrect. All changes are still non-destructive in your workflow and you can reverse 100% of them at all times. Just because you can't reverse them *in the exported file* doesn't mean they're not reversible. This is what you need to learn.

Eric Stevens
Thhe fact that you can't reverse them in the image file is what this argument is all about.

Doing them over again but differently is not reversing them.

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

Sandman
It is 100% truly reversible.

Eric Stevens
Not necessarily in the sense that Floyd and I use the term.

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.

Sandman
Yes they are, you just don't understand them. Nothing to be ashamed of, there are lots of things you don't understand.

Eric Stevens
You should ponder on those words.