Thread: [Lcms-user] How to create a gray profile with L-star grey response?

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[Lcms-user] How to create a gray profile with L-star grey response?

From: Marco F. <Mar...@en...> - 2016-05-24 10:54:22

Hi!

I'm trying to create a gray profile that has an L* (L-star) response curve, but I'm a little confused about the "parametric tone curve" syntax.

Is there an example how to create the correct tone curve? I guess I need the inverted version of L* companding, right? Would that be a 4 parametric curve, with:
y(Gamma) = 3.0
a=1.0/1.16
b=0.16/1.16
c=100.0/903.3
d=0.008856*903.3/100.0

So in code something like that:
cmsFloat64Number lStarParams[5] = { 3.0, 1.0/1.16, 0.16/1.16, 100.0/903.3, 0.008856*903.3/100.0 };
cmsBuildParametricToneCurve( ctx, 4, lStarParams );
???

Or is it as easy as passing a NULL for the TransferFunction parameter in cmsCreateGrayProfileTHR() because the response matches the PCS response?

Thanks,
Marco

Re: [Lcms-user] How to create a gray profile with L-star grey response?

From: Elle S. <ell...@ni...> - 2016-05-24 12:31:30

On 05/24/2016 06:54 AM, Marco Freudenberger wrote:
> Hi!
>
> I'm trying to create a gray profile that has an L* (L-star) response
> curve, but I'm a little confused about the "parametric tone curve" syntax.
>
> Is there an example how to create the correct tone curve? I guess I need
> the inverted version of L* companding, right? Would that be a 4
> parametric curve, with:
>
> y(Gamma) = 3.0
>
> a=1.0/1.16
>
> b=0.16/1.16
>
> c=100.0/903.3
>
> d=0.008856*903.3/100.0
>
> So in code something like that:
>
> cmsFloat64Number lStarParams[5] = { 3.0, 1.0/1.16, 0.16/1.16,
> 100.0/903.3, 0.008856*903.3/100.0 };
>

FWIW (I'm no expert!), I use these parameters to make the Lab parametric 
curve:

cmsFloat64Number labl_parameters[5] =
{ 3.0, 1.0/1.16, 0.16/1.16, 2700.0/24389.0, 0.08000 };

The parameters are from these two pages:

http://brucelindbloom.com/index.html?Eqn_RGB_to_XYZ.html
http://brucelindbloom.com/index.html?LContinuity.html

Where does the equation for your last parameter come from? I've always 
used Lindbloom's values and he gives 0.08.

Best,
Elle
-- 
http://ninedegreesbelow.com
Color management and free/libre photography

Re: [Lcms-user] How to create a gray profile with L-star grey response?

From: Marco F. <Mar...@en...> - 2016-05-24 13:07:29

Hi !

Thanks for your response,

looks like I'm on the right path, your solution looks pretty similar - and BTW, I take your comment that you are no expert as an understatement, I've visited your website a couple of times and think it's a great reference and shows a lot of knowledge and experience :-)

Regarding my last parameter value:
I indirectly took it off Bruce Lindbloom's site as well :-) Unfortunately, I missed the page you linked with the "Inverse Companding" somehow, I started at the "(forward) Companding" page (http://brucelindbloom.com/index.html?Eqn_RGB_to_XYZ.html) and did the math to revert it.

For the last parameter I started with:
e(epsilon) = 0.008856, K(kappa) = 903.3 
so I'm calculating: e' = e * K / 100.0 (as e <= e). It's very close to 0.08 anyways :-)

However, I used the numbers that Bruce lists as "Actual CIE Standard". Thanks to your second link (and I've seen that page before, but didn't remember it when I needed it ...) I realized that the values given as "Intent of the CIE Standard" as you are using them are probably the better values... and with e = 216/23489 and K = 23489/27, e' turns out to be 216/2700 = 2/25 = exactly 0.08...

Thanks and best regards,
Marco

PS - to the group: I'm still wondering what would happen if I'd simply set the TransferFunction to NULL...

-----Original Message-----
From: Elle Stone [mailto:ell...@ni...] 
Sent: Dienstag, 24. Mai 2016 14:08
To: lcm...@li...
Subject: Re: [Lcms-user] How to create a gray profile with L-star grey response?

On 05/24/2016 06:54 AM, Marco Freudenberger wrote:
> Hi!
>
> I'm trying to create a gray profile that has an L* (L-star) response 
> curve, but I'm a little confused about the "parametric tone curve" syntax.
>
> Is there an example how to create the correct tone curve? I guess I 
> need the inverted version of L* companding, right? Would that be a 4 
> parametric curve, with:
>
> y(Gamma) = 3.0
>
> a=1.0/1.16
>
> b=0.16/1.16
>
> c=100.0/903.3
>
> d=0.008856*903.3/100.0
>
> So in code something like that:
>
> cmsFloat64Number lStarParams[5] = { 3.0, 1.0/1.16, 0.16/1.16, 
> 100.0/903.3, 0.008856*903.3/100.0 };
>

FWIW (I'm no expert!), I use these parameters to make the Lab parametric
curve:

cmsFloat64Number labl_parameters[5] =
{ 3.0, 1.0/1.16, 0.16/1.16, 2700.0/24389.0, 0.08000 };

The parameters are from these two pages:

http://brucelindbloom.com/index.html?Eqn_RGB_to_XYZ.html
http://brucelindbloom.com/index.html?LContinuity.html

Where does the equation for your last parameter come from? I've always used Lindbloom's values and he gives 0.08.

Best,
Elle
--
http://ninedegreesbelow.com
Color management and free/libre photography

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Re: [Lcms-user] How to create a gray profile with L-star grey response?

From: Florian H. <lis...@ho...> - 2016-05-24 13:18:58

Hi,

Am 24.05.2016 um 15:07 schrieb Marco Freudenberger:
> PS - to the group: I'm still wondering what would happen if I'd simply set the TransferFunction to NULL...

That would result in a gamma 1.0 response I think (according to the ICC
spec).

Florian.

Re: [Lcms-user] How to create a gray profile with L-star grey response?

From: Marco F. <Mar...@en...> - 2016-05-24 14:14:33

Marti,
 sorry, I'm not sure I understand your answer.

My intention is gray with L*, not Linear gray (Gamma 1.0), using the cmsBuildGamma would give me a gamma 1.0 response curve, though - at least when used with cmsCreateGrayProfile, right? Or am I missing something?

Are you suggesting I'm creating the profile "low level"? Something like:

cmsHPROFILE hProfile = cmsCreateProfilePlaceholder(ctx);
cmsSetProfileVersion(hProfile, 4.3);
cmsSetDeviceClass(hProfile, cmsSigDisplayClass);	// or better abstract?    
cmsSetColorSpace(hProfile, cmsSigGrayData);   
cmsSetPCS(hProfile, cmsSigLabData);
cmsSetHeaderRenderingIntent(hProfile, INTENT_RELATIVE_COLORIMETRIC);
SetTextTags(hProfile, L"gray L-star")
cmsCIEXYZ wpxyz;
cmsxyY2XYZ(&wpxyz, WhitePoint);
cmsWriteTag(hProfile, cmsSigMediaWhitePointTag, &wpxyz);
cmsToneCurve* tc = cmsBuildGamma(ctx, 1.0); // 1.0 gamma from Lab = L* ???????
cmsWriteTag(hProfile, cmsSigGrayTRCTag, (void*)tc));
cmsFreeToneCurve(tc);




-----Original Message-----
From: Marti Maria [mailto:mar...@li...] 
Sent: Dienstag, 24. Mai 2016 15:50
To: Marco Freudenberger; 'Florian Höch'; lcm...@li...
Subject: RE: [Lcms-user] How to create a gray profile with L-star grey response?

Right, mark the PCS as Lab and use cmdBuildGamma(NULL, 1.0). You only need to add the white point and this curve.

Marti Maria
The LittleCMS project
http://www.littlecms.com 

-----Original Message-----
From: Florian Höch [mailto:lis...@ho...]
Sent: martes, 24 de mayo de 2016 15:19
To: lcm...@li...
Subject: Re: [Lcms-user] How to create a gray profile with L-star grey response?

Hi,

Am 24.05.2016 um 15:07 schrieb Marco Freudenberger:
> PS - to the group: I'm still wondering what would happen if I'd simply 
> set
the TransferFunction to NULL...

That would result in a gamma 1.0 response I think (according to the ICC spec).

Florian.

----------------------------------------------------------------------------
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Mobile security can be enabling, not merely restricting. Employees who bring their own devices (BYOD) to work are irked by the imposition of MDM restrictions. Mobile Device Manager Plus allows you to control only the apps on BYO-devices by containerizing them, leaving personal data untouched!
https://ad.doubleclick.net/ddm/clk/304595813;131938128;j
_______________________________________________
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Re: [Lcms-user] How to create a gray profile with L-star grey response?

From: Marti M. <mar...@li...> - 2016-05-24 13:48:15

Right, mark the PCS as Lab and use cmdBuildGamma(NULL, 1.0). You only need
to add the white point and this curve.

Marti Maria
The LittleCMS project
http://www.littlecms.com 

-----Original Message-----
From: Florian Höch [mailto:lis...@ho...] 
Sent: martes, 24 de mayo de 2016 15:19
To: lcm...@li...
Subject: Re: [Lcms-user] How to create a gray profile with L-star grey
response?

Hi,

Am 24.05.2016 um 15:07 schrieb Marco Freudenberger:
> PS - to the group: I'm still wondering what would happen if I'd simply set
the TransferFunction to NULL...

That would result in a gamma 1.0 response I think (according to the ICC
spec).

Florian.

----------------------------------------------------------------------------
--
Mobile security can be enabling, not merely restricting. Employees who bring
their own devices (BYOD) to work are irked by the imposition of MDM
restrictions. Mobile Device Manager Plus allows you to control only the apps
on BYO-devices by containerizing them, leaving personal data untouched!
https://ad.doubleclick.net/ddm/clk/304595813;131938128;j
_______________________________________________
Lcms-user mailing list
Lcm...@li...
https://lists.sourceforge.net/lists/listinfo/lcms-user

Re: [Lcms-user] How to create a gray profile with L-star grey response?

From: Marti M. <mar...@li...> - 2016-05-24 14:17:31

Hi,

Yes, that one. If you use cmsBuildGamma() you are forced to XYZ PCS, but if
you use low-level you can use Lab PCS as well.

Regards
Marti Maria
The LittleCMS project
http://www.littlecms.com 


-----Original Message-----
From: Marco Freudenberger [mailto:Mar...@en...] 
Sent: martes, 24 de mayo de 2016 16:14
To: Marti Maria <mar...@li...>; 'Florian Höch'
<lis...@ho...>; lcm...@li...
Subject: RE: [Lcms-user] How to create a gray profile with L-star grey
response?

Marti,
 sorry, I'm not sure I understand your answer.

My intention is gray with L*, not Linear gray (Gamma 1.0), using the
cmsBuildGamma would give me a gamma 1.0 response curve, though - at least
when used with cmsCreateGrayProfile, right? Or am I missing something?

Are you suggesting I'm creating the profile "low level"? Something like:

cmsHPROFILE hProfile = cmsCreateProfilePlaceholder(ctx);
cmsSetProfileVersion(hProfile, 4.3);
cmsSetDeviceClass(hProfile, cmsSigDisplayClass);	// or better
abstract?    
cmsSetColorSpace(hProfile, cmsSigGrayData);   
cmsSetPCS(hProfile, cmsSigLabData);
cmsSetHeaderRenderingIntent(hProfile, INTENT_RELATIVE_COLORIMETRIC);
SetTextTags(hProfile, L"gray L-star") cmsCIEXYZ wpxyz; cmsxyY2XYZ(&wpxyz,
WhitePoint); cmsWriteTag(hProfile, cmsSigMediaWhitePointTag, &wpxyz);
cmsToneCurve* tc = cmsBuildGamma(ctx, 1.0); // 1.0 gamma from Lab = L*
???????
cmsWriteTag(hProfile, cmsSigGrayTRCTag, (void*)tc)); cmsFreeToneCurve(tc);




-----Original Message-----
From: Marti Maria [mailto:mar...@li...]
Sent: Dienstag, 24. Mai 2016 15:50
To: Marco Freudenberger; 'Florian Höch'; lcm...@li...
Subject: RE: [Lcms-user] How to create a gray profile with L-star grey
response?

Right, mark the PCS as Lab and use cmdBuildGamma(NULL, 1.0). You only need
to add the white point and this curve.

Marti Maria
The LittleCMS project
http://www.littlecms.com 

-----Original Message-----
From: Florian Höch [mailto:lis...@ho...]
Sent: martes, 24 de mayo de 2016 15:19
To: lcm...@li...
Subject: Re: [Lcms-user] How to create a gray profile with L-star grey
response?

Hi,

Am 24.05.2016 um 15:07 schrieb Marco Freudenberger:
> PS - to the group: I'm still wondering what would happen if I'd simply 
> set
the TransferFunction to NULL...

That would result in a gamma 1.0 response I think (according to the ICC
spec).

Florian.

----------------------------------------------------------------------------
--
Mobile security can be enabling, not merely restricting. Employees who bring
their own devices (BYOD) to work are irked by the imposition of MDM
restrictions. Mobile Device Manager Plus allows you to control only the apps
on BYO-devices by containerizing them, leaving personal data untouched!
https://ad.doubleclick.net/ddm/clk/304595813;131938128;j
_______________________________________________
Lcms-user mailing list
Lcm...@li...
https://lists.sourceforge.net/lists/listinfo/lcms-user

Re: [Lcms-user] How to create a gray profile with L-star grey response?

From: Marco F. <Mar...@en...> - 2016-05-24 14:21:46

OK, I'll give it a shot and try it. 

Thanks again, Elle, Marti, Florian for your answers!

Marco

-----Original Message-----
From: Marti Maria [mailto:mar...@li...] 
Sent: Dienstag, 24. Mai 2016 16:19
To: Marco Freudenberger; 'Florian Höch'; lcm...@li...
Subject: RE: [Lcms-user] How to create a gray profile with L-star grey response?

Hi,

Yes, that one. If you use cmsBuildGamma() you are forced to XYZ PCS, but if you use low-level you can use Lab PCS as well.

Regards
Marti Maria
The LittleCMS project
http://www.littlecms.com 

-----Original Message-----
From: Marco Freudenberger [mailto:Mar...@en...]
Sent: martes, 24 de mayo de 2016 16:14
To: Marti Maria <mar...@li...>; 'Florian Höch'
<lis...@ho...>; lcm...@li...
Subject: RE: [Lcms-user] How to create a gray profile with L-star grey response?

Marti,
 sorry, I'm not sure I understand your answer.

My intention is gray with L*, not Linear gray (Gamma 1.0), using the cmsBuildGamma would give me a gamma 1.0 response curve, though - at least when used with cmsCreateGrayProfile, right? Or am I missing something?

Are you suggesting I'm creating the profile "low level"? Something like:

cmsHPROFILE hProfile = cmsCreateProfilePlaceholder(ctx); cmsSetProfileVersion(hProfile, 4.3);
cmsSetDeviceClass(hProfile, cmsSigDisplayClass);	// or better
abstract?    
cmsSetColorSpace(hProfile, cmsSigGrayData);   
cmsSetPCS(hProfile, cmsSigLabData);
cmsSetHeaderRenderingIntent(hProfile, INTENT_RELATIVE_COLORIMETRIC); SetTextTags(hProfile, L"gray L-star") cmsCIEXYZ wpxyz; cmsxyY2XYZ(&wpxyz, WhitePoint); cmsWriteTag(hProfile, cmsSigMediaWhitePointTag, &wpxyz);
cmsToneCurve* tc = cmsBuildGamma(ctx, 1.0); // 1.0 gamma from Lab = L* ???????
cmsWriteTag(hProfile, cmsSigGrayTRCTag, (void*)tc)); cmsFreeToneCurve(tc);

-----Original Message-----
From: Marti Maria [mailto:mar...@li...]
Sent: Dienstag, 24. Mai 2016 15:50
To: Marco Freudenberger; 'Florian Höch'; lcm...@li...
Subject: RE: [Lcms-user] How to create a gray profile with L-star grey response?

Right, mark the PCS as Lab and use cmdBuildGamma(NULL, 1.0). You only need to add the white point and this curve.

Marti Maria
The LittleCMS project
http://www.littlecms.com 

-----Original Message-----
From: Florian Höch [mailto:lis...@ho...]
Sent: martes, 24 de mayo de 2016 15:19
To: lcm...@li...
Subject: Re: [Lcms-user] How to create a gray profile with L-star grey response?

Hi,

Am 24.05.2016 um 15:07 schrieb Marco Freudenberger:
> PS - to the group: I'm still wondering what would happen if I'd simply 
> set
the TransferFunction to NULL...

That would result in a gamma 1.0 response I think (according to the ICC spec).

Florian.

----------------------------------------------------------------------------
--
Mobile security can be enabling, not merely restricting. Employees who bring their own devices (BYOD) to work are irked by the imposition of MDM restrictions. Mobile Device Manager Plus allows you to control only the apps on BYO-devices by containerizing them, leaving personal data untouched!
https://ad.doubleclick.net/ddm/clk/304595813;131938128;j
_______________________________________________
Lcms-user mailing list
Lcm...@li...
https://lists.sourceforge.net/lists/listinfo/lcms-user