Lenses and sharpening

In article , Eric Stevens
wrote:

I couldn't see the difference at all, but then I didn't want to push
the screen with excessive brightness. Instead I relied on the
subtraction and the histogram to find the differences, which were
almost zero.

'almost zero' is not zero.

you are actually proving my point.

nospam has backed off considerably from his original views but I
expect that won't stop him from trumpeting them again in the future.

i have *not* done any such thing. stop lying and twisting what i say.

i have *always* said it's not lossless and it is not.

There is nothing you do in image processing which is not lossless.

straw man.

For
some reason the conversion of RGB -- Lab has been particularly
singled out for criticism in this respect.

it's a bad workflow because what can be done with an rgb-lab-rgb
conversion can be done *without* the conversion and with better
results.

this is a fact, no matter how much you or anyone else say otherwise.

It's as lossless as anything else you can do.

it's more lossy than not doing the conversions.

In article , Eric Stevens
wrote:

Yes, and it's common to evrything you do. So why does converting to
Lab allegedly make it so much worse?

The bigger question is; Why would anybody use LAB at all these days,
but for some arcane process few folks are using?

Read http://tinyurl.com/malzpsu

a book by dan margulis is a complete waste of time and money. he has
constantly been proven wrong by pretty much everyone else in the
industry.

a much better choice is color management for photographers by andrew
rodney, and/or real world color management by bruce fraser, chris
murphy and fred bunting. they know what they're talking about.

short answer: there is no reason to use lab except in very specific
edge cases that just about everyone will never encounter.

There is no real benefit from using LAB in a daily Photoshop workflow
given the massive changes in the various tools and PS algorithms since
the days of PS6 & PS7, you might have noticed that PS CC 2014 is
currently = PS 15.1.0.

Quite true.

So far the only reason those who actually use LAB for some purpose or
another can give (Peter says he likes to sharpen in LAB, when what he
means is he likes to over sharpen using any method he can get his hands
on) is some guru writing 20 years ago has claimed that it is the way to
go. Frankly for most photographers running current editions of PS
CS5/CS6/CC/CC 2014), using LAB for anything other than some sort of
specialized work, is a waste of time, and trying to find some way to
defend its use in a never ending Usenet screech-fest thread, is an even
bigger waste of time.

For a start, it's great for getting rid of haze.

switching to lab to get rid of haze??

In article , Eric Stevens
wrote:

notice the differences at the left end of the histogram.

however, this is about round-tripping from rgb to lab and then back.
you only did half.

Fir comment. I've just compared the original JPG with a copy -- Lab
-- JPG again. JPGs are RGB are they not?

usually but not always

Then what else might they be and under what circumstances?

cmyk

OK, but RGB is the default.

not if your source image is cmyk.

The only conclusion I can reach is that there is no difference
between
a PSD created from a RGB file and a PSD created from the same image
when it has first been converted from RGB to Lab.

there is. it may not be a huge difference, but there is a difference.

As soon as you do anything in Photoshop there is a difference due to
rounding errors (quantization) but is this all you are objecting to?

you do realize that adds up, right?

Yes, and it's common to evrything you do. So why does converting to
Lab allegedly make it so much worse?

i didn't say converting to lab was much worse.

i said that rgb-lab-rgb is not lossless. you may not care about the
loss, but it's definitely there.

margulis is wrong.

Read this extract from the exchange at
https://www.ledet.com/margulis/ACT_p...LAB-damage.htm

================================================== ===========
From: Dan Margulis,
Date: Tue, Apr 24, 2001, 9:53 AM
[colortheory] A real world example of the RGBLABRGB debate...

Stephen writes,

I was very shocked at the effects of the simple mode change from
RGBLABRGB on APS4 and 5.5. Here are the links so you can view the
differences, and download and see for yourself:

What seems to have happened here is that the file was intended to
be Adobe RGB, but during conversion to LAB it was assumed that it was
an sRGB file. That will, of course, hose all the colors. The
possibility of such hijinks is a major reason that many users avoid
Adobe RGB.

Treating this as an Adobe RGB file, and converting RGBLABRGB
five times, I get the normal result, no variation of any significance,
quality-wise or statistical.

Dan Margulis

P.S. If this file were properly converted to sRGB, this would be
an example of the kind of file that *wouldn't* convert well, because
so much of it is close to the edge of the gamut. But sRGBLABsRGB,
although not lossless, would be better than, for example, sRGBAdobe
RGBsRGB.
================================================== =============

Dan Margulis is not making simple blanket statements capable of being
rebutted in the same fashion. Also, look at the date.

the date is irrelevant.

the math hasn't changed.

he's changing the rules, as he always does. *that* conversion might
have had argb/srgb issues but *others* don't.

he was wrong then and he's still wrong.


do you see people arguing to edit jpegs? of course not.

What exactly do you mean by that?

you say you can't see a difference in an rgb-lab-rgb conversion and you
subtracted them and saw all black, therefore, you have deemed them to
be equivalent.

I didn't say that. Read it all again carefully. I compared an
rgb-lab-rgb conversion to the original JPG.

you said you saw black when subtracting them.

I also pointed out the significance of the resulting histogram.

that's where the differences can be seen.

if you do the same for jpeg, you will also not see a difference, and if
you subtract, you'll also see all black. therefore, a jpeg should be
equivalent to an original raw.

That is squiffy logic and it's not even a good parody of what I did.

it's *exactly* the same logic.

you're position is if you can't see it then there is no difference.

Rubbish. My position is that even if there is a difference, the
difference doesn't matter if you can't see it.

that may be true now, but what if somewhere down the line you want to
do further processing? you now have a degraded image.

that's why people shoot and edit raw, because even though you can't see
a difference with jpeg, it makes a difference.

the reality is that there *is* a difference. you might not consider the
difference to be significant (and indeed it is is very small), but
there *is* a difference, therefore it is *not* lossless.

bottom line: rgb-lab-rgb offers no benefit (other than possibly
contrived edge cases nobody will ever encounter).

You have backed off considerably from your original opinion on this
matter.

no i haven't at *all*.

stop lying about what i say.

Don't be such an overly sensitive git. I said nothing specific about
what you said. I said that you have backed off considerably from your
original opinion in this matter. That is nothing that you said. It is
something that *I* said.

i have not backed off at all. i have always said it's a lossy process.

you saying i have backed off is a lie.

I've done considerable reading about this matter since you raised it
and I now have a much better understanding about where the problems
might lie. The conversion to and from say RGB to Lab and vice versa
can be lossy,

is lossy.

but so too can the conversions from (say) ProPhotoRGB to
aRGB, from aRGB to sRGB and vice versa.

yes, and?

Also, to or from any of these
to CMYK. The problem is not the colour system but the colour space
used by that system. You can see that that is really the problem when
you read the discussion cited by nospam.

you cited it.

(Any) RGB to Lab is not a problem as Lab has an enormously wide gamut,
way into the regions of imaginary colours. But it's very easy to
create colours in Lab for which there is no place in any system using
RGB. Now that is where things can get lost.

that's a different issue.

On 10/5/2014 9:05 PM, nospam wrote:
In article , PeterN
wrote:

However, LAB is great for color changes that maintain subtle
tonality. e.g channel swapping.

you must be kidding.

Why?

channel swapping is hardly subtle, *especially* in lab.

Who said channel swapping was subtle.

you did.

Where? Show thee message #.


--
PeterN

On 10/5/2014 9:05 PM, nospam wrote:
In article , PeterN
wrote:


I gaae him some common uses. He typically uses "edge case' to give him
wriggle room.

wrong again.

what i call an edge case is an edge case and what you're calling common
can be done *without* lab more easily and with better quality results.

in other words, you're blaming others for your own lack of knowledge
and unwillingness to learn.

Well then explain with facts and detail.
Warning. I have Dan's book and will use it as a reference.

that's your problem. dan is wrong and reading his books has led you
astray.

if you read other books, you'll see that they consistently prove just
how much of an idiot dan really is. i've mentioned two such books in
this thread and other books in other threads.


The procedures in his book work just fine for me, and others.
http://www.dgrin.com/showthread.php?t=18308


I presented proof. As usual, you have presented nothing.
You want to persist., go argue with yourself.


--
PeterN

On 10/5/2014 9:05 PM, nospam wrote:
In article , PeterN
wrote:

You have never noticed the ease of a color change in LAB, compared to
making a similar color change in RGB.

YOu have never brought out color using LAB that could not easily be
brought out in RGB.

nonsense.

you just don't know how to do it in rgb.

Well let's see a FACTUAL comparison.

read the books i've already mentioned.

you won't, because you only want to argue.


Show some proof. As I said earlier, I just want to keep people from
believing your nonsense.
You have never proven a thing, except yur favorite line.

--
PeterN

On 10/5/2014 9:05 PM, nospam wrote:
In article , Eric Stevens
wrote:

I couldn't see the difference at all, but then I didn't want to push
the screen with excessive brightness. Instead I relied on the
subtraction and the histogram to find the differences, which were
almost zero.

'almost zero' is not zero.

you are actually proving my point.

nospam has backed off considerably from his original views but I
expect that won't stop him from trumpeting them again in the future.

i have *not* done any such thing. stop lying and twisting what i say.

i have *always* said it's not lossless and it is not.

There is nothing you do in image processing which is not lossless.

straw man.

For
some reason the conversion of RGB -- Lab has been particularly
singled out for criticism in this respect.

it's a bad workflow because what can be done with an rgb-lab-rgb
conversion can be done *without* the conversion and with better
results.

Yes it can be done in RGB, but with a lot more effort.
Take a simple example stock photo and change the color in RGB, and then
make the same color change in LAB.

Or, simply increase color saturation n RGB and make the same change in LAB.
All yo do is sout questionable theory. Show some real life proof.



this is a fact, no matter how much you or anyone else say otherwise.

It's as lossless as anything else you can do.

it's more lossy than not doing the conversions.



--
PeterN

On 2014.10.05, 20:55 , PeterN wrote:
On 10/5/2014 6:57 PM, Alan Browne wrote:
On 2014.10.05, 14:42 , PeterN wrote:

We went through all this some many months ago. I demonstrated clearly
that the amount of 'loss' was negligible in practical terms.


I would use the terem "color change." anstead of loss.

Any change is a quality loss. Whether that is colour difference, tone,
brightness, sharpness ... whatever, it's a loss.


Then you are using a different definition of quality.

Not at all. A non lossy process would have:

RGB-A -- X-format -- RGB-B

with RGB-A identical to RGB-B

But - the fact is that with Lab

RGB-A -- Lab -- RGB-B

RGB-A =/= RGB-B, therefore there was quality loss.

--
Among Broad Outlines, conception is far more pleasurable
than “carrying [the children] to fruition.”
Sadly, “there’s a high infant mortality rate among
Broad Outlines—they often fall prey to Nonstarters.”
"Bestiary of Intelligence Writing" - CIA

On Sun, 05 Oct 2014 21:05:19 -0400, nospam
wrote:

In article , PeterN
wrote:


I gaae him some common uses. He typically uses "edge case' to give him
wriggle room.

wrong again.

what i call an edge case is an edge case and what you're calling common
can be done *without* lab more easily and with better quality results.

in other words, you're blaming others for your own lack of knowledge
and unwillingness to learn.

Well then explain with facts and detail.
Warning. I have Dan's book and will use it as a reference.

that's your problem. dan is wrong and reading his books has led you
astray.

if you read other books, you'll see that they consistently prove just
how much of an idiot dan really is. i've mentioned two such books in
this thread and other books in other threads.

You seem to have a thing about Lab color. Your comments are quite
unbalanced. You don't seem to have a good comment about *any* aspect
of it. What happened to you?
--

Regards,

Eric Stevens

On Sun, 05 Oct 2014 21:05:21 -0400, nospam
wrote:

In article , Eric Stevens
wrote:

I couldn't see the difference at all, but then I didn't want to push
the screen with excessive brightness. Instead I relied on the
subtraction and the histogram to find the differences, which were
almost zero.

'almost zero' is not zero.

you are actually proving my point.

nospam has backed off considerably from his original views but I
expect that won't stop him from trumpeting them again in the future.

i have *not* done any such thing. stop lying and twisting what i say.

i have *always* said it's not lossless and it is not.

There is nothing you do in image processing which is not lossless.

straw man.

Not at all. If you are going to criticise conversions to Lab on the
graonds that they incur losses, then you have to acknowledge that
there are other things you can do in Photoshop which are equally
lossy.

For
some reason the conversion of RGB -- Lab has been particularly
singled out for criticism in this respect.

it's a bad workflow because what can be done with an rgb-lab-rgb
conversion can be done *without* the conversion and with better
results.

'Bad' is a value judgement. Why should your value judgement be taken
any more seriously than anyone elses?

this is a fact, no matter how much you or anyone else say otherwise.

It's as lossless as anything else you can do.

it's more lossy than not doing the conversions.

So is editing/retouching the image.
--

Regards,

Eric Stevens