Lenses and sharpening

On 10/4/2014 4:41 PM, Eric Stevens wrote:
On Sat, 04 Oct 2014 04:48:23 -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?

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.

Do you mean where he says:

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

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?

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)."

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.

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.

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.

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.


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

--
PeterN

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.

In article , PeterN
wrote:

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

hilarious.

then someone with amnesia doesn't have memory loss, it's that their
memories have changed. got it!

On 10/4/2014 5:45 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.



Since the new smaret sharpen algorithm came out, I rarely sue LAB for
sharpening. However, LAB is great for color changes that maintain subtle
tonality. e.g channel swapping.

--
PeterN

In article , PeterN
wrote:

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

you must be kidding.

On Sun, 05 Oct 2014 14:57:51 -0400, 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?
--

Regards,

Eric Stevens

In article , Eric Stevens
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.

On 10/5/2014 2:41 PM, nospam wrote:
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.


Such as?


--
PeterN

On 10/5/2014 2:41 PM, nospam wrote:
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.


Well let's see a FACTUAL comparison.


The above are "edge cases."

if you say so.



--
PeterN

On 10/5/2014 2:41 PM, nospam wrote:
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.


Well explain exactly what you call edge cases.
Should be easy for you, since you have experience workng in LAB..




--
PeterN