Re: Color Model

[Bernhard Herzog]

"C. Ecker" <address@hidden> writes:

> - CMYK: would be great to have. AFAIK, it requires to change the internal
> representation of the color, because CMYK contains additional information
> compared to RGB, i.e. by transforming a color from CMYK to RGB information
> is lost. Therefore each color in skencil should be represented internaly
> in CMYK-format instead of RGB as it is now.

I think Skencil should be able to work with both RGB and CMYK.  Both
color models have different gamuts and different uses.  If your Drawing
is intended for the web you want RGB, if it's for professional printing,
you want CMYK.  proper CMYK support needs some form of color management,
so adding CMYK isn't exactly trivial.


> - Transparency: In 0.7 transparency is limited to the fill.

Actually, it's limited to the uniform fill.  It should be extended to
all fills.

> Is there a
> reason for not allowing transparency also for the line color attribute ?

Lack of implementation, mostly.  Line opacity should be about as
difficult to add as fill opacity was.  Line opacity is as such is not
very useful if you fill and stroke an object, though, because the fill
shows through in half of the line.  Object opacity which defines the
opacity for an entire object (perhaps even a group) is probably more
useful in that case, but it's more work to implement.

> In other applications transparency and color values are always bundled,
> i.e.  everywhere a color appears there is an associated transparency
> value. 

I'm not sure that really is the best model to follow.  At least it's not
all of it.  It's quite desirable to be able to specify opacities in
places where a color as such doesn't make much sense, e.g. object
opacity.  Also, if you look at PDF or SVG, the opacity isn't part of the
color, although you can specifiy an opacity in addition to a color in
many places.

>   The "bundling" would mean to either directly implemented transparency
> into the color model or to introduce additional transparency parameters
> for the line color and gradients points.

I'd probably prefer the latter.

On the whole, anybody who wants to work on opacity should have a look at
how PDF (>= 1.4) and SVG handle it.  The models they use are important
because Skencil will have to be able to read and write those formats to
an extent.

   Bernhard

-- 
Intevation GmbH                                 http://intevation.de/
Skencil                                           http://skencil.org/
Thuban                                  http://thuban.intevation.org/