FW: Proposed resolution of DR 17-0019 and DR 17-0028

[Rex Jaeschke]

We’ve just reviewed and agreed to adopt the following text, probably with “may” changed to “might” in various places.

 

Rex

 

From: Francis Cave [mailto:francis at franciscave.com] 
Sent: Tuesday, November 14, 2017 4:14 PM
To: Rex Jaeschke (rex at RexJaeschke.com) <rex at rexjaeschke.com>; MURATA, Makoto (eb2m-mrt at asahi-net.or.jp) <eb2m-mrt at asahi-net.or.jp>
Subject: Proposed resolution of DR 17-0019 and DR 17-0028

 

Rex, Murata-san

Here is my proposed resolution of both DR 17-0019 and DR 17-0028. The DR text is largely the same, because they both concern the same element, schemeClr, specified in §20.1.2.3.29. There is tutorial text about color spaces in §L.4.1.5 and about color transforms in §L.4.8.3. As I have stated previously, the fact that color transforms can be used in combinations is not clearly explained anywhere, and there is only one example (in §20.1.2.3.16) of more than one color transform element being used in combination.

I have thought about adding references from the normative text in §20.1.2.3 to the Primer, but this would be inconsistent - I cannot find any specific references from normative text to the Primer. Instead, I propose to add some more normative text to provide some cross-references to the main elements for specifying colors.

Here is revised text for the introduction to §20.1.2.3, based upon my earlier contribution

Kind regards,

Francis

 

20.1.2.3 Colors

Given its own section within DrawingML Basics, cColors are an integral part of the DrawingML framework. Colors are used in virtually every object to help describe it's appearance when it is rendered on the screen. Since not every generating application wishes to represent color in the same manner, it is possible to specify color in a number of different ways.



A color is specified by a base color value, which may optionally be modified by one or more color transforms. A base color value is specified in accordance with one of the following color models:

- Red, Green, Blue (RGB) color model, with values expressed either as percentages (§20.1.2.3.30) or as hex digits (§20.1.2.3.32)
- Hue, Saturation, Luminance (HSL) color model (§20.1.2.3.13)
- Scheme-based color model (§20.1.2.3.29)
- Color Presets color model (§20.1.2.3.22)
- Operating system color model (§20.1.2.3.33)

A base color may be modified by one or more transforms. The effect of specifying a color using a combination of several transforms is application-dependent.



[Note: When combining multiple color transforms, the order in which the transforms are specified is likely to be significant in terms of how the color is rendered by the application. end note]

I propose that there should be some additional guidance in the Primer on these points. 



L.4.1.5 Colors

...

These different models allow document authors the choice as to which color model would be appropriate for their particular application. Each of these is detailed within the DrawingML Basics reference material. For further guidance see §L.4.8.2.

...

L.4.8.2 Color Models

There are several methods of expressing color: scrgbClr, srgbClr, hslClr, sysClr, schemeClr, and prstClr. Although srgbClr is the most commonly used model, the rationale for having various equivalent color models stems from a desire to have different ways of naturally expressing a color choice. A color may also be expressed by specifying a base color using any of the above methods and transforming this in a systematic way using one or more color transforms. For further guidance on color transforms see §L.4.8.3.

...

L.4.8.3 Color Transforms

...

*	invGamma: Yields the inverse sRGB gamma shift of its input color.

Any number of color transforms may be combined in order to modify a base color. The order in which the color transforms are specified is significant in terms of the end result of the transformation. The effect is application-dependent and may or may not make sense in specific cases.





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