Re: [Lcms-user] How to transform across profiles with different whitepoints?

[Lukas S. <som...@gm...>]

Thanks a lot for the explication!

Lukas Sommer


Am Mo., 27. Okt. 2025 um 13:00 Uhr schrieb <mar...@li...>:

> Hi Lukas,
>
>
>
> Human vision is capable to discount the chromaticity of media or the light
> that illuminates that media.
>
>
>
> https://en.wikipedia.org/wiki/Chromatic_adaptation
>
>
>
> The ICC way to do color management assumes you want this behavior by
> default. Light used to illuminate the media is always discounted.
> Chromaticity of the media is controlled by the rendering intent. “absolute
> colorimetric” means to NOT discount the media color. You normally should
> use “perceptual” or “relative colorimetric plus black point compensation” ,
> as you normally want to model full adaptation. That is, consider unprinted
> paper is “white” no matter different papers may be of different color.
>
>
>
> LittleCMS can also deal with the light, by using cmsSetAdaptationState(),
> but this is an advanced feature that may confuse you. Use only if strictly
> needed.
>
>
>
> So, to answer your question, you have just to use intent perceptual or
> relative colorimetric and white points are handled automatically by
> profiles.
>
>
>
> Hope that helps
>
>
>
> Marti Maria
>
> The LittleCMS Project
>
> https://www.littlecms.com
>
>
>
>
>
>
>
> *From:* Lukas Sommer <som...@gm...>
> *Sent:* Monday, October 27, 2025 1:31 PM
> *To:* Lcm...@li...
> *Subject:* [Lcms-user] How to transform across profiles with different
> whitepoints?
>
>
>
> Hello!
>
>
>
> I've a question about correct treatment of profiles with different
> whitepoints.
>
>
>
> Consider the following code:
>
>
>
> ///////////////////////////////////////////////////////////////////////////
>
>             cmsHPROFILE srgbProfileHandle = cmsCreate_sRGBProfile(); //
> D65?
>
>
>
>             cmsHPROFILE cielabProfileHandle = cmsCreateLab4Profile(
>                 // nullptr means: Default white point (D50)
>                 // TODO Does this make sense? sRGB, for example, has
>                 // D65 as whitepoint…
>
>                 nullptr);
>
>
>
>             auto m_transform = cmsCreateTransform(
>                 cielabProfileHandle, // input profile handle
>                 TYPE_Lab_DBL, // input buffer format
>                 rgbProfileHandle, // output profile handle
>                 TYPE_RGB_DBL, // output buffer format
>                 INTENT_ABSOLUTE_COLORIMETRIC, // rendering intent
>                 cmsFLAGS_NOCACHE // flags
>
>             );
>
> ///////////////////////////////////////////////////////////////////////////
>
>
>
> Now, I suppose srgbProfileHandle is D65 and cielabProfileHandle is D50?
>
>
>
> Is it allowed to create simply the transform like in the example, and to
> rely on LCMS to do the conversion? Or do I have to make a white point
> adaption before?
>
>
>
> Best regards
>
>
>
> Lukas
>