Re: [CREATE] ORA spec: adding additional layer effects

Hi,

I'm working on a new CSS composting spec that will add those missing blend
modes.
There will be a new CSS keyword 'blending' that will let you specify a
blend mode on an HTML or SVG element.

Rik

On Sat, Feb 25, 2012 at 7:06 AM, Alexandre Prokoudine <
alexandre.prokoudine@gmail.com> wrote:

> Hi,
>
> As far as I can tell,
> http://dev.w3.org/SVG/modules/compositing/master/ doesn't cover the
> use case either.
>
> What would be your recommendation?
>
> Alexandre Prokoudine
> http://libregraphicsworld.org
>
> ---------- Forwarded message ----------
> From: Andrew Chadwick <a.t.chadwick@gmail.com>
> Date: Sat, Feb 25, 2012 at 2:19 AM
> Subject: [CREATE] ORA spec: adding additional layer effects
> To: create@lists.freedesktop.org, mypaint-discuss <mypaint-discuss@gna.org
> >
>
>
> The OpenRaster spec currently states (working from memory here) that
> ORA files may use uses the SVG compositing ops[1]. These do not
> provide colorize layer modes, nor modes for luminosity-setting,
> hue-setting or saturation-setting. I'd quite like to implement these
> but because it would require a change to the OpenRaster specification,
> I haven't yet. Users are clamouring for it however, and I think
> MyPaint should implement colourize at least (not to mention I have
> some sample code kicking around locally).
>
> Currently layers with compositing modes other than "svg:src-over" are
> written to layers.xml with a suitable "composite-op" attribute:
>
>  <layer composite-op="svg:src-over" opacity="1.0"
> src="data/layer001.png" visibility="visible" x="0" y="0" />
>
> What I suggest doing is extending the current definition with the
> following modes:
>
> * SOMEPREFIXhue - src hue, and luminance and saturation of the dst
> * SOMEPREFIXsaturation - saturation of the src layer, with the hue and
> luminance of the dst
> * SOMEPREFIXcolor - hue and saturation of the src, with the luminance of
> the dst
> * SOMEPREFIXluminosity - luminance of the src, over the hue and
> saturation of the dst
>
> Definitions of these blending modes can be found in various PDF
> specifications[2], and work well up until one has to composite with an
> opacity setting using scaled ints. Which is a whole new kind of fun.
>
> What should we use for SOMEPREFIX? "pdf:blend-" is one possibility if
> we want to slavishly adopt that... but I'd rather refer to a more open
> specification if I can (not to mention that I want to use the Rec. 709
> primaries[3] for the perceptual-ish bit). Current SVG specification
> (1.1) is indeed luminosity/luma aware for feColorMatrix, but does not
> define these blend modes, sadly.
>
> MyPaint could of course just do its own thing here, or copy Krita.
> I've had a quick poke around the Krita and GIMP implementations of
> these layer modes, but they seem to use HSV only, which seems
> limiting. Is there any particular reason for this?
>
>
> [1] http://www.w3.org/TR/SVGCompositing/
> [2] The shortest and most relevant one is probably the "PDF Blend
> Modes: Addendum" for the PDF Reference, fifth edition, version 1.6,
> dated Jan 23 2006 - available from Adobe via your search engine of
> choice.
> [3] https://en.wikipedia.org/wiki/Rec._709
>
> --
> Andrew Chadwick
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