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Today's Topics:
1. Re: Adding better LCH support to GIMP 2.10 (Elle Stone)
2. Re: Adding better LCH support to GIMP 2.10 (Sven Claussner)
3. Re: Adding better LCH support to GIMP 2.10 (Elle Stone)
4. Re: Adding better LCH support to GIMP 2.10 (Partha Bagchi)
5. Re: Adding better LCH support to GIMP 2.10 (?yvind Kol?s)
----------------------------------------------------------------------
Message: 1
Date: Sun, 14 Feb 2016 12:44:04 -0500
From: Elle Stone <ellestone ninedegreesbelow com>
To: gimp-developer-list gnome org
Subject: Re: [Gimp-developer] Adding better LCH support to GIMP 2.10
Message-ID: <56C0BCE4 2020809 ninedegreesbelow com>
Content-Type: text/plain; charset=windows-1252; format=flowed
I received an email complaining that it was not true that as located on
the LCH color wheel, sRGB Blue was blatantly violet, sRGB Red was on the
orange side of red, sRGB Green was on the yellow side of green, and sRGB
Yellow as on the green side of yellow.
There is a sliver of truth in the complaint. On the LCH color wheel, my
statement is true.
However, LAB/LCH was designed to measure color differences, not to serve
as a color appearance model, even though it often gets used as such.
Also the LAB color space is particularly bad when it comes to dealing
with blues and violets.
For comparison, here are JCH and LCH values reported using the ArgyllCMS
xicclu tool:
Hue JCH/LCH
sRGB Blue 301 [LCh]
sRGB Blue 273 [JCh] (still on the violet side of blue, but not
blatantly violet)
sRGB Green 134 [LCh]
sRGB Green 140 [JCh] (not as far towards yellow)
sRGB Red 41 [LCh]
sRGB Red 32 [JCh] (not as far towards orange)
sRGB Yellow 100 [LCh]
sRGB Yellow 111 [JCh] (farther towards green)
As you can see from these values, according to JCH model, sRGB Blue is
still on the violet side of the JCH color wheel. But it's not nearly as
far on the violet side of the JCH color wheel as it is on the LCH color
wheel.
For both color wheels, sRGB Green is on the yellow side of green, sRGB
Red is on the orange side of red, and sRGB Yellow is on the green side
of yellow.
If you would like to check for yourself:
Here's the handprint.com CIECAM (JCH) color wheel:
http://www.handprint.com/HP/WCL/cwheel06.html
Here's the handprint.com CIELAB (LCH) color wheel:
http://www.handprint.com/HP/WCL/labwheel.html
Here's the xicclu commands for checking the LCH/JCH values for sRGB
colors using an sRGB ICC profile:
xicclu -ir -pJ sRGB-elle-V2-g10.icc
xicclu -ir -pL sRGB-elle-V2-g10.icc
Here's a link to the xicclu documentation:
http://argyllcms.com/doc/xicclu.html
Here's a link to download ICC profiles:
http://ninedegreesbelow.com/photography/lcms-make-icc-profiles.html
It would be very nice if GIMP users had a way to pick colors using the
LCH color wheel or better yet the JCH color wheel. Either color space is
a vast improvement over the pathetically inadequate HSV.
Best,
Elle
------------------------------
Message: 2
Date: Sun, 14 Feb 2016 21:56:19 +0100
From: Sven Claussner <scl gplus gmail com>
To: gimp-developer-list gnome org
Subject: Re: [Gimp-developer] Adding better LCH support to GIMP 2.10
Message-ID: <56C0E9F3 3060605 gmail com>
Content-Type: text/plain; charset=windows-1252; format=flowed
Hi,
@Elle: you are speaking here of the JCH color model (or space) and
mentioned
on your website [1] that JAB and JCH have outdated LAB and LCH
(which are often considered the high end image editing color
spaces/models).
Searching a while for more information about JCH I found only very few
information, even not on other color management and FOSS graphics devel
mailing lists. Only on the PXLab website [2] I see a short description:
JCH:=The CIE Color Appearance Model (1997) with viewing and scene
conditions
to be defined separately.
I'm failing to understand all its implications.
Can you tell us more about JCH and JAB and why you consider it to
be a good choice, please? What about LAB and LCH then?
Does somebody else here know more about it?
Thank you in advance
Sven
[1]
http://ninedegreesbelow.com/photography/high-bit-depth-gimp-tutorial-edit-tonality-color-separately.html
[2]
http://irtel.uni-mannheim.de/pxlab/doc/api/de/pxlab/pxl/ColorSpaceCodes.html#CS_JCh
------------------------------
Message: 3
Date: Sun, 14 Feb 2016 18:33:39 -0500
From: Elle Stone <ellestone ninedegreesbelow com>
To: Gimp-developer <gimp-developer-list gnome org>
Subject: Re: [Gimp-developer] Adding better LCH support to GIMP 2.10
Message-ID: <56C10ED3 3070000 ninedegreesbelow com>
Content-Type: text/plain; charset=windows-1252; format=flowed
On 02/14/2016 03:56 PM, Sven Claussner wrote:
Hi,
@Elle: you are speaking here of the JCH color model (or space) and
mentioned
on your website [1] that JAB and JCH have outdated LAB and LCH
(which are often considered the high end image editing color
spaces/models).
Searching a while for more information about JCH I found only very few
information, even not on other color management and FOSS graphics devel
mailing lists. Only on the PXLab website [2] I see a short description:
JCH:=The CIE Color Appearance Model (1997) with viewing and scene
conditions
to be defined separately.
I'm failing to understand all its implications.
Can you tell us more about JCH and JAB and why you consider it to
be a good choice, please? What about LAB and LCH then?
I can't tell you very much about JCH/JAB because I'm still trying to
figure it all out myself.
You might try plowing your way through this PDF:
http://rit-mcsl.org/fairchild/PDFs/AppearanceLec.pdf
This page has links to some equations:
https://en.wikipedia.org/wiki/CIECAM02
This page briefly talks about color appearance models in more
down-to-earth terms:
http://www.rit-mcsl.org/fairchild/WhyIsColor/Questions/4-8.html
An internet search on terms like Color appearance model, Mark Fairchild,
and CIECAM02 will turn up a lot of material. None of it is easy reading.
LAB answers the question "how far apart do colors have to be before the
average human observer will say 'those are different colors'". The
"home" of LAB was for use with quality control for colors in textiles,
printing, and such. LAB wasn't designed to be used as a color space for
editing, but it works pretty well for a lot of different editing tasks.
A full understanding of LAB would require understanding the kinds of
experiments that were done to map out "when is color X different enough
from color Y to be seen as visually different?" I have no idea what kind
of experiments were done or how the mathematical model was constructed
from the experimental results. But the resulting equations to convert
from XYZ to LAB and then LCH are pretty straightforward.
Color appearance models are designed to answer a very different and much
more complicated set of questions. They try to answer questions like
"How to describe colors?", "Why does the appearance of one color change
when juxtaposed next to another color?", and "Why does a surface look
the same color even when the light shining on it changes drastically
(for example from bright daylight to deep shade or to tungsten lighting,
or even in the shadow side of an object)?".
These are complicated questions, being answered using complicated
research and complicated resulting models described by complicated sets
of equations. Also color appearance models are a very active area of
ongoing research, so what's considered really good today might be
superceded tomorrow.
My reasons for suggesting that for use in GIMP (1)LAB/LCH is good and
(2)JAB/JCH is probably better are so simplistic that you'll all just laugh:
1. Bruce MacEvoy's handprint.com website on watercolor pigments switched
from using LCH to using JCH to give paint pigment colors, and I respect
Bruce MacEvoy as an authority on giving useable values for paint
pigments: http://handprint.com/HP/WCL/water.html,
http://handprint.com/LS/CVS/color.html
2. Mark Fairchild seems to think CIECAM02 is a pretty good color
apperance model, though again this is a field of active research, and
much of what Mark Fairchild writes goes right over my head.
3. ArgyllCMS and LCMS already incorporate the equations for JAB/JCH in
their code, as does RawTherapee, so it has to be not too difficult to
code up for GIMP. But my (very limited) efforts to make sense of the
ArgyllCMS/LCM/RT code have so far been unsuccessful.
I find the LCH blend modes, color picker, and Hue-Chroma tool to be
incredibly useful. The few people who've written to me about using my
patched GIMP seem very enthusiastic.
JCH apparently is more accurate than LCH for describing colors. I'm not
sure how much difference the "more accurate" would make in the digital
darkroom. It would be nice to be able to give JCH a try, but in the
meantime I can't imagine going back to editing without LCH.
Does somebody else here know more about it?
No doubt even my short description above needs a lot of corrections!
Thank you in advance
Sven
[1]
http://ninedegreesbelow.com/photography/high-bit-depth-gimp-tutorial-edit-tonality-color-separately.html
[2]
http://irtel.uni-mannheim.de/pxlab/doc/api/de/pxlab/pxl/ColorSpaceCodes.html#CS_JCh
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List address: gimp-developer-list gnome org
List membership:
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------------------------------
Message: 4
Date: Sun, 14 Feb 2016 19:25:44 -0500
From: Partha Bagchi <partha1b gmail com>
To: Elle Stone <ellestone ninedegreesbelow com>, Sven Claussner
<scl gplus gmail com>
Cc: Gimp-developer <gimp-developer-list gnome org>
Subject: Re: [Gimp-developer] Adding better LCH support to GIMP 2.10
Message-ID:
<CAOW9c=9+UuSCbbTeWeE32rLq036vtefyguxPG=
VanDOy3ui9PA mail gmail com>
Content-Type: text/plain; charset=UTF-8
First hit when you google:
http://www.colourphil.co.uk/lab_lch_colour_space.shtml
On Sun, Feb 14, 2016 at 6:33 PM, Elle Stone <
ellestone ninedegreesbelow com>
wrote:
On 02/14/2016 03:56 PM, Sven Claussner wrote:
Hi,
@Elle: you are speaking here of the JCH color model (or space) and
mentioned
on your website [1] that JAB and JCH have outdated LAB and LCH
(which are often considered the high end image editing color
spaces/models).
Searching a while for more information about JCH I found only very few
information, even not on other color management and FOSS graphics devel
mailing lists. Only on the PXLab website [2] I see a short description:
JCH:=The CIE Color Appearance Model (1997) with viewing and scene
conditions
to be defined separately.
I'm failing to understand all its implications.
Can you tell us more about JCH and JAB and why you consider it to
be a good choice, please? What about LAB and LCH then?
I can't tell you very much about JCH/JAB because I'm still trying to
figure it all out myself.
You might try plowing your way through this PDF:
http://rit-mcsl.org/fairchild/PDFs/AppearanceLec.pdf
This page has links to some equations:
https://en.wikipedia.org/wiki/CIECAM02
This page briefly talks about color appearance models in more
down-to-earth terms:
http://www.rit-mcsl.org/fairchild/WhyIsColor/Questions/4-8.html
An internet search on terms like Color appearance model, Mark Fairchild,
and CIECAM02 will turn up a lot of material. None of it is easy reading.
LAB answers the question "how far apart do colors have to be before the
average human observer will say 'those are different colors'". The "home"
of LAB was for use with quality control for colors in textiles, printing,
and such. LAB wasn't designed to be used as a color space for editing,
but
it works pretty well for a lot of different editing tasks.
A full understanding of LAB would require understanding the kinds of
experiments that were done to map out "when is color X different enough
from color Y to be seen as visually different?" I have no idea what kind
of
experiments were done or how the mathematical model was constructed from
the experimental results. But the resulting equations to convert from XYZ
to LAB and then LCH are pretty straightforward.
Color appearance models are designed to answer a very different and much
more complicated set of questions. They try to answer questions like "How
to describe colors?", "Why does the appearance of one color change when
juxtaposed next to another color?", and "Why does a surface look the same
color even when the light shining on it changes drastically (for example
from bright daylight to deep shade or to tungsten lighting, or even in
the
shadow side of an object)?".
These are complicated questions, being answered using complicated
research
and complicated resulting models described by complicated sets of
equations. Also color appearance models are a very active area of ongoing
research, so what's considered really good today might be superceded
tomorrow.
My reasons for suggesting that for use in GIMP (1)LAB/LCH is good and
(2)JAB/JCH is probably better are so simplistic that you'll all just
laugh:
1. Bruce MacEvoy's handprint.com website on watercolor pigments switched
from using LCH to using JCH to give paint pigment colors, and I respect
Bruce MacEvoy as an authority on giving useable values for paint
pigments:
http://handprint.com/HP/WCL/water.html,
http://handprint.com/LS/CVS/color.html
2. Mark Fairchild seems to think CIECAM02 is a pretty good color
apperance
model, though again this is a field of active research, and much of what
Mark Fairchild writes goes right over my head.
3. ArgyllCMS and LCMS already incorporate the equations for JAB/JCH in
their code, as does RawTherapee, so it has to be not too difficult to
code
up for GIMP. But my (very limited) efforts to make sense of the
ArgyllCMS/LCM/RT code have so far been unsuccessful.
I find the LCH blend modes, color picker, and Hue-Chroma tool to be
incredibly useful. The few people who've written to me about using my
patched GIMP seem very enthusiastic.
JCH apparently is more accurate than LCH for describing colors. I'm not
sure how much difference the "more accurate" would make in the digital
darkroom. It would be nice to be able to give JCH a try, but in the
meantime I can't imagine going back to editing without LCH.
Does somebody else here know more about it?
No doubt even my short description above needs a lot of corrections!
Thank you in advance
Sven
[1]
http://ninedegreesbelow.com/photography/high-bit-depth-gimp-tutorial-edit-tonality-color-separately.html
[2]
http://irtel.uni-mannheim.de/pxlab/doc/api/de/pxlab/pxl/ColorSpaceCodes.html#CS_JCh
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List membership:
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List archives: https://mail.gnome.org/archives/gimp-developer-list
_______________________________________________
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List address: gimp-developer-list gnome org
List membership:
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List archives: https://mail.gnome.org/archives/gimp-developer-list
------------------------------
Message: 5
Date: Mon, 15 Feb 2016 08:24:00 +0100
From: ?yvind Kol?s <pippin gimp org>
To: Elle Stone <ellestone ninedegreesbelow com>
Cc: Gimp-developer <gimp-developer-list gnome org>
Subject: Re: [Gimp-developer] Adding better LCH support to GIMP 2.10
Message-ID:
<CAKjrkdNbdbmgz8ruVC=
b3j4qVFHObVYmQZ0E7j0f7Y11P7jw3A mail gmail com>
Content-Type: text/plain; charset=UTF-8
On Mon, Feb 15, 2016 at 12:33 AM, Elle Stone
<ellestone ninedegreesbelow com> wrote:
This page briefly talks about color appearance models in more
down-to-earth
terms: http://www.rit-mcsl.org/fairchild/WhyIsColor/Questions/4-8.html
An internet search on terms like Color appearance model, Mark Fairchild,
and
CIECAM02 will turn up a lot of material. None of it is easy reading.
Color Appearance Models are even more in the realm of the subjective
phenomenological experience of color than CIE XYZ / CIE Lab - and less
useful in an attempt at absolutely defining/describing a color outside
the context/scene where it is experiences/observed. With a color
appearance model the squares A and B in the Checker Shadow Illusion (
https://en.wikipedia.org/wiki/Checker_shadow_illusion ) would have
different colors - since they *appear* to have different colors.
Through color constancy this affects not only the apparent luminanace
but also the apparent hue of colors in a scene.
/pippin
------------------------------
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