Re: [office] Draft for enhanced colors

[Regina Henschel <regina.henschel@libreoffice.org>]

Hi Andreas,

Andreas J Guelzow schrieb am 29.03.2023 um 22:04:
> Hi,
>
> I am missing the point of these "enhanced colours", or how these 
> "enhanced colours" are in fact enhanced.
>
> All colours are representable as #rrggbb. How they are presented by a 
> consumer or were presented by a producer of an ODF file is completely in 
> the control of that producer or consumer. So it seems to me that these 
> "enhanced colours" do not provide any new features that applications 
> using ODF could not already provide.
>
> On the other hand, adding the possibility of storing colours in these 
> other encoding ways in ODF requires all consumers to know how to 
> translate them into #rrggbb. So while it may be simpler for an 
> application that wants to use these "enhanced colours" to store them 
> directly, this is traded off against all other consumers having to be 
> able to understand these enhanced colours.
>
> So please elaborate what would be gained by this for the ODF community.

I have thought again about RGBZeroToOne. You are right. To be usable for 
the "scrgbClr" color type of OOXML we would have to specify the 
conversion to sRGB, an unnecessary effort for no benefit for the ODF 
community. I'll remove the related parts.

A "scheme" is a collection of colors that harmonize with each other and 
give the document a certain look. Such a scheme is stored in the 
document and individual colors are then selected by reference. This has 
the following advantages, for example:
* Because the colors combined in the scheme are stored completely in the 
document, these colors are also available on other computers even if 
individual colors have not yet been actively used. This makes it easier 
to work together on a document.
* Document templates with scheme colors can be passed on easily, because 
the colors combined in the scheme are stored completely in the document 
template.
* Since the scheme is stored in the document, the colors are available 
again after saving and loading. This makes it easier to edit documents 
that take longer to process.
* Objects designed with scheme colors automatically adapt to a new 
environment when copied and pasted. This makes it easier to reuse 
already existing objects in new environment.
* Without changing structure and content, different looks can be 
produced quickly by changing the scheme.

Apart from better interoperability with OOXML these are values in 
itself. LibreOffice is going to implement schemes.

Color transformations make it easy to create related color changes 
starting from a base color. The information which base color was used is 
now kept when saving and loading. This is advantageous when editing is 
not done in one go.
The possibilities already available through the "draw:start-intensity" 
and "draw:end-intensity" attributes are very limited because only a 
reduction of the intensity is possible and it is only available for 
gradients.
So extending color definitions with color transformations and providing 
the ability to store these information is useful. You could store the 
resulting sRGB-color, but that would lose the base color.
Color transformations give a better interoperability with OOXML. 
LibreOffice is going to implement color transformations for luminance.

And in regard to multi-color gradients, which are contained in my second 
draft: Multi-color gradients are a frequently expressed user wish. Such 
gradients are known from SVG (also in ODF). However, the gradient types 
of SVG differ from the gradients types defined with <draw:gradient> 
elements. In order to fulfill the user wishes, it should also be 
possible to define gradients with multiple colors for gradients defined 
with <draw:gradient> elements.

Kind regards,
Regina