Color and tone adjustments specifications need improvement

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

Hi all,

This is about problems I see in the specification of draw:blue, 
draw:red, draw:gree, draw:luminance, draw:contrast, and draw:gamma. I 
have not written a JIRA issue yet, because I do not know, how cases with 
multiple, connected problems are handled.

1.
The ODF specification does not provide any information how the 
draw:gamma value has to be used when rendering an image.
The .png format has a chunk gAMA, which holds a gamma value. 
http://www.w3.org/TR/PNG/#3gamma. And in that specification you get a 
detailed description, how this value is to be used for displaying a .png 
picture. http://www.w3.org/TR/PNG/#13Decoder-gamma-handling. I think the 
ODF specification needs such kind of description too.

2.
The attribute draw:blue has already a description (and thereby 
draw:green and draw:red).Such description is missing for draw:contrast 
and draw:luminance.

3.
In the specification of draw:blue the output value is restricted to the 
interval given by the color depth. But in AOO this restriction is done 
only after draw:luminance, draw:contrast, and draw:gamma are applied 
too. ODF 1.2 specification does not consider the other filters at all.

4.
The gamma-filter is non-linear. When combining it with another filter, 
the result depends on the order in which the filters are applied. ODF 
1.2 specification does not contain an information about the order. The 
schema has <interleave> for the elements of 
"style-graphic-properties-attlist".

5.
The data type of draw:gamma is "percent". That would include 
non-positive values too. But in all cases I have found, it is a positive 
value. In fact applications often restrict the values in the UI, e.g. 
PaintShopPro 0.2 to 5.0, IrfanView 0.01 to 6.99, AOO 0.1 to 10.0.

6.
It is possible to set a background to an image using draw:fill. ODF1.2 
specification does not state, whether the filters are applied to the 
background too. In AOO the background is not affected.

7.
ODF 1.2 specification uses "pixel image" and "bitmap or raster graphic". 
It is not clear to me, whether that is the same. If yes, the same 
wording should be used in all places.

8.
In AOO the color and tonal adjustments work on metafiles and .svg 
graphics too, for example characters in metafiles or gradients in .svg 
graphics are affected by the color filters. Therefore "pixel" or 
"raster" might not be correct at all.

I have written a description based on the way AOO does it. Because plain 
text is not so good for formulas, I have attached the description as 
.odt document. The document is not meant as ready proposal, but to 
illustrate, what I'm missing.

Kind regards
Regina

Attachment: OASIS.odt
Description: application/vnd.oasis.opendocument.text