Lenses and sharpening

On 2014-10-04 20:41:46 +0000, Eric Stevens said:

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?

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.

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.


--
Regards,

Savageduck

On 2014.10.04, 16:47 , Eric Stevens wrote:
On Sat, 04 Oct 2014 10:57:31 -0400, Alan Browne
wrote:

On 2014.10.03, 23:29 , Eric Stevens wrote:
On Thu, 18 Sep 2014 19:14:58 -0400, nospam
wrote:

--- snip ---

and the one after that,

RGBLABRGB is damage free, but CMYKLABCMYK is not.
I disagree. If you start out with all of the same spaces for RGB and
CMYK, and use only those spaces - then convert to and from Lab, you
will get some quantization errors with both.

and andrew rodney's post:
RGBLABRGB is damage free
You1re not serious are you Dan?
Take an RGB file. Duplicate it. Do an RGB to LAB to RGB conversion
and subtract the two. You can turn on or off the 8 bit dither. When
you subtract the two and create a new document and look at the
Histogram in Levels, you will see there certainly is data loss and a
change. Move the sliders of the Levels Histogram over and you1ll see
the effects of what differences between the two files you produced.
Are you saying this isn1t data loss?

that test is trivial to do. try it yourself.

This one continues to bother me. I am still inclined to agree with Dan
Margulis. I'm not quite sure what procedure Andrew Rodney is proposing
to prove his point so, using Photoshop CC, I have carried out my own
test as follows:

1. Find a JPG with a suitable range of colors. This one came from my
wife's collection:
https://dl.dropboxusercontent.com/u/...20IMG_2154.jpg
I saved a copy as a PSD (see below for the reason).

2. Copy and convert to Lab. I couldn't save to JPG from Lab so I saved
to PSD. See
https://dl.dropboxusercontent.com/u/...54-via-Lab.jpg

3. I then loaded the two PSD files into a new file as separate layers.
(1) above was the background layer and (2) was the next. I subtracted
the 2nd layer from the first with the result shown in
https://dl.dropboxusercontent.com/u/...Difference.jpg
That's right: solid black.

4. To confirm the point I took a screen shot. See
https://dl.dropboxusercontent.com/u/...t%20Screen.jpg
Note the histogram. All of the pixels appear to be down at the zero
end of the scale: that is, jet black.

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.

I'm not wedded to the perfection of the method I have used and I would
be interested to hear from anyone who has a meaningful criticism.

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

Procedu

1. An original in JPG
2. The original converted to LAB version
3. The LAB version converted to JPG.

delta 1-2, delta 2-3.

In the deltas you will see the actual difference (hard to see unless
your screen is turned up bright) and it is not something that would be
noticeable in an actual screen or print of a shot.

I couldn't see the difference at all, but then I didn't want to push

On a good screen (which I have) I don't need to brighten up to see them,
but I do have to look hard.

the screen with excessive brightness. Instead I relied on the
subtraction and the histogram to find the differences, which were
almost zero.

'subtraction' is what I mean by 'delta' above. Same difference wot.


--
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 10/4/14 PDT, 2:45 PM, Savageduck wrote:
On 2014-10-04 20:41:46 +0000, Eric Stevens said:

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?

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.

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.


Using LAB in your workflow is 20th C. But some like it that way. Heck,
get out the chemicals if you want!

So, the Duck is right on the mark, again.

On Sat, 04 Oct 2014 17:08:28 -0400, nospam
wrote:

In article , Eric Stevens
wrote:

4. To confirm the point I took a screen shot. See
https://dl.dropboxusercontent.com/u/...t%20Screen.jpg
Note the histogram. All of the pixels appear to be down at the zero
end of the scale: that is, jet black.

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.


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.

compare a high quality jpeg with the original and you'll see black as
you did above, but there are definitely differences (and actually, less
of a difference than the rgb-lab conversion).

What is the difference with rgb-Lab-rgb conversions and what causes
them?

read the link and pay attention to andrew rodney.

Do you mean where he says:

"ANY colorspace conversion can cause these quantization errors (RGB
to RGB as an example)."

that's part of it.

ignore marguilis, not just in that link but in general. he has claimed
that 16 bit editing was a waste, which it absolutely is not. i dunno if
he still claims it but he probably does.

I bet you are quoting him out of context.

nope.

http://www.brucelindbloom.com/index.html?DanMargulis.html
...If an example is presented that shows an 8-bit/16-bit difference,
a rule is immediately created, on-the-spot, that disqualifies the
image. None of Dan's original six conditions would disqualify a
ProPhoto image (you can read these conditions below in section I),
but it appears as though ProPhoto images are no longer acceptable. If
one takes this technique to its logical conclusion, Dan's 16-bit
challenge would become "When considering all images showing no 16-bit
advantage, 16-bit images show no advantage."

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.

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.

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

(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.
--

Regards,

Eric Stevens

On Sat, 4 Oct 2014 14:45:01 -0700, Savageduck
wrote:

On 2014-10-04 20:41:46 +0000, Eric Stevens said:

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

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.
--

Regards,

Eric Stevens

On Sat, 04 Oct 2014 17:08:30 -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. For
some reason the conversion of RGB -- Lab has been particularly
singled out for criticism in this respect.

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

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

Regards,

Eric Stevens

On 2014.10.04, 18:58 , John McWilliams wrote:
On 10/4/14 PDT, 2:45 PM, Savageduck wrote:
On 2014-10-04 20:41:46 +0000, Eric Stevens said:

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?

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.

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.


Using LAB in your workflow is 20th C. But some like it that way. Heck,
get out the chemicals if you want!

For some colour work it is the shortest path. I don't use it often, but
it's saved me time when really needed.


So, the Duck is right on the mark, again.

Surely - and he pointed out that there are exceptions too.


--
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 10/4/2014 4:48 AM, nospam wrote:
In article , Eric Stevens
wrote:

4. To confirm the point I took a screen shot. See
https://dl.dropboxusercontent.com/u/...t%20Screen.jpg
Note the histogram. All of the pixels appear to be down at the zero
end of the scale: that is, jet black.

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

Anyway I still got an
apparently all-black screen and here is the screen shot showing the
histogram:
https://dl.dropboxusercontent.com/u/...screen%202.jpg

An even tighter all-black bar than previously.

this is all explained in the link you gave. try reading it.

You don't have to be rude. Try reading it yourself and then explain
step by step what you think he is proposing.

i'm not trying to be rude. the answers really are in the link and i've
said this many times already.

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?

compare a high quality jpeg with the original and you'll see black as
you did above, but there are definitely differences (and actually, less
of a difference than the rgb-lab conversion).

What is the difference with rgb-Lab-rgb conversions and what causes
them?

read the link and pay attention to andrew rodney.

ignore marguilis, not just in that link but in general. he has claimed
that 16 bit editing was a waste, which it absolutely is not. i dunno if
he still claims it but he probably does.

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.

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.

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).


IOW you you have never worked in LAB

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.

The above are "edge cases."

--
PeterN

In article , PeterN
wrote:

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


IOW you you have never worked in LAB

i have, and quite a bit. lab is useful for certain tasks, but photo
editing isn't one of them.

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.

The above are "edge cases."

if you say so.

On 10/4/2014 10:57 AM, Alan Browne wrote:
On 2014.10.03, 23:29 , Eric Stevens wrote:
On Thu, 18 Sep 2014 19:14:58 -0400, nospam
wrote:

In article , Eric Stevens
wrote:

I have found that using high pass on the luminiscence layer in LAB
tends to minimize halos.

Actually it is a good idea to do any/all/most sharpening on a
luminosity layer, LAB or not.

not always, since the conversion to lab and back is not lossless.

Not strictly correct:

it is completely correct.

we went through this about six months ago, and apparently will again.

https://www.ledet.com/margulis/ACT_p...LAB-damage.htm


" I have always thought that moving from either CMYK or RGB to Lab
and back was a damage free process, that is, you would end up with
the same color co-ordinates when you arrived back from Lab mode.

"RGBLABRGB is damage free, but CMYKLABCMYK is not. The damage
isn't all that great, so in many images it pays to come out of CMYK
so as to take advantage of LAB's strengths; sharpening, however, is
not one of these cases.
....
Dan Margulis"

you clearly don't understand what you're reading, since that link
agrees with what i said!

as the other posts in your link clearly show, dan margulis is wrong (as
he is about a lot of things).

read the *very* next post, from chris murphy,

Converting to and from Lab has never been a damage free process.

and the one after that,

RGBLABRGB is damage free, but CMYKLABCMYK is not.
I disagree. If you start out with all of the same spaces for RGB and
CMYK, and use only those spaces - then convert to and from Lab, you
will get some quantization errors with both.

and andrew rodney's post:
RGBLABRGB is damage free
You1re not serious are you Dan?
Take an RGB file. Duplicate it. Do an RGB to LAB to RGB conversion
and subtract the two. You can turn on or off the 8 bit dither. When
you subtract the two and create a new document and look at the
Histogram in Levels, you will see there certainly is data loss and a
change. Move the sliders of the Levels Histogram over and you1ll see
the effects of what differences between the two files you produced.
Are you saying this isn1t data loss?

that test is trivial to do. try it yourself.

This one continues to bother me. I am still inclined to agree with Dan
Margulis. I'm not quite sure what procedure Andrew Rodney is proposing
to prove his point so, using Photoshop CC, I have carried out my own
test as follows:

1. Find a JPG with a suitable range of colors. This one came from my
wife's collection:
https://dl.dropboxusercontent.com/u/...20IMG_2154.jpg
I saved a copy as a PSD (see below for the reason).

2. Copy and convert to Lab. I couldn't save to JPG from Lab so I saved
to PSD. See
https://dl.dropboxusercontent.com/u/...54-via-Lab.jpg


3. I then loaded the two PSD files into a new file as separate layers.
(1) above was the background layer and (2) was the next. I subtracted
the 2nd layer from the first with the result shown in
https://dl.dropboxusercontent.com/u/...Difference.jpg
That's right: solid black.

4. To confirm the point I took a screen shot. See
https://dl.dropboxusercontent.com/u/...t%20Screen.jpg
Note the histogram. All of the pixels appear to be down at the zero
end of the scale: that is, jet black.

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.

I'm not wedded to the perfection of the method I have used and I would
be interested to hear from anyone who has a meaningful criticism.

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

Procedu

1. An original in JPG
2. The original converted to LAB version
3. The LAB version converted to JPG.

delta 1-2, delta 2-3.

In the deltas you will see the actual difference (hard to see unless
your screen is turned up bright) and it is not something that would be
noticeable in an actual screen or print of a shot.


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

--
PeterN