nospam
In article <87y4tkzksh.fld@barrow.com>, Floyd L. Davidson <floyd@apaflo.com>wrote:

Floyd L. Davidson
UnSharpMask is not reversible.

nospam
it is with a non-destructive workflow.

Floyd L. Davidson
I'm sorry that you don't understand the meaning of that.

nospam
i absolutely do know the meaning, since it's all i use.

it's you who doesn't understand what a non-destructive workflow means

Floyd L. Davidson
A non-destructive workflow means you can *undo* and then *redo*.

That is not a reversible function.

nospam
it is to the user, which is what matters.

in other words, the user sharpens today and then tomorrow or next month or whenever, they can readjust it or remove it entirely. that means to the user, it's reversible.

that's why a non-destructive workflow is so powerful.

Floyd L. Davidson
Non-destructive is wonderful.

nospam
yes it is. it's one of the bests thing to happen to workflow.

Floyd L. Davidson
It especially impresses Chicken Little, Humpty Dumpty and nospam and probably other cartoon characters.

nospam
resorting to insults means you're full of shit.

a non-destructive workflow is *much* more flexible, powerful and productive than the old-fashioned way, which is why millions of photographers practice it, including ones more famous than you.

Floyd L. Davidson
But no matter how you try to squirm, no matter how you squeal, *unsharp mask is a nonreversible function*.

nospam
the function is not used standalone so that doesn't matter.

people use a non-destructive workflow so that any adjustment can be reversed and/or modified after the fact.

you need to climb out of you narrow-minded thinking and look at what the rest of the world actually does and why they do it.

Floyd L. Davidson
For example, you can add sharpening with a high pass sharpen tool to an image, save it as a JPEG, send it to someone else, and they can use a blur tool to reverse the sharpen.

nospam
not perfectly. you even said 'virtually reverses' in your description.

that's another way of saying 'there is some loss.'

Floyd L. Davidson
I don't see the term "virtually reverses" in that sentence.

nospam
look again:

Using one and then the other virtually reverses the results.

Floyd L. Davidson
But the previous reference is in fact precise. The reason for saying "virtually reverses"

nospam
so you admit you said it after all.

Floyd L. Davidson
is because if the sharpen and blur algorithms are not exactly the same and using precisely the correct parameters, the reversal isn't total. Which is to say that if it is done by inspection the result will be such that there is no visible difference.

nospam
no visible difference is another way of saying there's a difference, but you just can't see it.

there's no visible difference between a high quality jpeg and the original either. in fact, the difference is barely there even under close inspection.

Floyd L. Davidson
If it is actually measured, there will be an insignificant difference.

nospam
so there is a difference, just as i said.

Floyd L. Davidson
I'm sorry that you have so much difficulty with precision use of language.

nospam
i'm not the one with the difficulties.

Floyd L. Davidson
In article <87bnqh1mby.fld@barrow.com>, Floyd L. Davidson <floyd@apaflo.com>wrote:

nospam
Not the case. It is the high pass sharpen tool that is the inverse of blur. They can use the exact same algorithm with different parameters. Using one and then the other virtually reverses the results.

Floyd L. Davidson
If the sharpening is done with UnsharpMask that cannot be done. USM is not reversible.

nospam
in a destructive workflow that is true.

in a non-destructive workflow, it is not true.

Floyd L. Davidson
Obviously you didn't understand what the term "reversible" means, and thought non-destructive is the same. It isn't.

nospam
i didn't say it was the same.

Floyd L. Davidson
See: http://en.wikipedia.org/wiki/Reversible_computing

Then read this,

http://en.wikipedia.org/wiki/Undo

And note the distinction between reversible and a non-linear undo.

nospam
non-destructive workflow is not non-linear undo.

you are once again talking out your butt and refusing to acknowledge that you don't know something and that there are alternate ways of doing things.