I am getting some unusual results sometimes when i use the Neon Edge Detection Filter parameters: 9, 3.0
Is there someone I could correspond directly with to send an example original photo and the processed one. I did mention this briefly about a year ago but wish to go into it in more depth.
Thank you.

*- david *

*Regards,David RosenthalCitySoft, Inc.(917) 922-2113* *www.citysoftinc.com *

On Mon, Feb 15, 2016 at 2:24 AM, wrote:

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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
To: gimp-developer-list@gnome.org
Subject: Re: [Gimp-developer] Adding better LCH support to GIMP 2.10 Message-ID:
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
To: gimp-developer-list@gnome.org
Subject: Re: [Gimp-developer] Adding better LCH support to GIMP 2.10 Message-ID:
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
To: Gimp-developer
Subject: Re: [Gimp-developer] Adding better LCH support to GIMP 2.10 Message-ID:
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:
https://mail.gnome.org/mailman/listinfo/gimp-developer-list List archives: https://mail.gnome.org/archives/gimp-developer-list

------------------------------

Message: 4 Date: Sun, 14 Feb 2016 19:25:44 -0500 From: Partha Bagchi
To: Elle Stone , Sven Claussner
Cc: Gimp-developer
Subject: Re: [Gimp-developer] Adding better LCH support to GIMP 2.10 Message-ID:

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 address: gimp-developer-list@gnome.org List membership:
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------------------------------

Message: 5 Date: Mon, 15 Feb 2016 08:24:00 +0100 From: ?yvind Kol?s
To: Elle Stone
Cc: Gimp-developer
Subject: Re: [Gimp-developer] Adding better LCH support to GIMP 2.10 Message-ID:

Content-Type: text/plain; charset=UTF-8

On Mon, Feb 15, 2016 at 12:33 AM, Elle Stone 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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