- From: Rik Cabanier <cabanier@gmail.com>
- Date: Tue, 8 Nov 2011 21:25:13 -0800
- To: Alex Danilo <alex@abbra.com>
- Cc: www-svg <www-svg@w3.org>, public-fx@w3.org
- Message-ID: <CAGN7qDDAj=v2xnbO42tcFE-AaTvHE1N-kVJzm=MprHT7BMC3Hw@mail.gmail.com>
On Tue, Nov 8, 2011 at 9:22 PM, Alex Danilo <alex@abbra.com> wrote: > Hi Rik, > > --Original Message--: > > > > > >>a. split up the spec in 2 sections: Porter-Duff & Blending. > > > >Agreed, it separates the two concepts properly. > > > >>Porter-Duff are compositing primitives that describes how 2 images > (src+dst) can be merged. > > > >Here, I'd agree with David Baron's comment and change the names to > 'source' and 'dest' in > >line with CSS spec. readability. > > > >That sounds fine. > > > > > > > >>Blending describes how the top image will 'blend' with its underlying > colors. The result of this is a new blended image. So far, we assume that > after blending, this image is composited with Porter-Duff src-over. > > > >No it doesn't. > > > >The SVG compositing spec does. > >Some of the blending modes talk about doing 'src-over' or 'dst-over' > depending on the color, but I believe that's a bug. > > That is a bug for sure. > > >If the blending was designed to be compatible with Adobe's model, > src-over IS implied. > >If you look at basic compositing formula in the PDF reference manual ( > https://www.adobe.com/content/dam/Adobe/en/devnet/pdf/pdfs/PDF32000_2008.pdf section > 11.3.3), you will see that it is using 'src-over'. > > I am intimately knowledgable with those functions and yes PDF is using > src-over. But there's > no reason to limit it to just that. > Great! I believe we're in agreement. > > > > >Blending describes how the colour channels mix. It is independent of the > P-D operators. > >The diagram in the existing spec. attempts to describe that. i.e. the one > that has a square > >with 4 sections - one multi-coloured, one blue, one yellow and one white. > > > >Blending applies only to the multi-colour area whilst P-D manages how the > different > >'regions' combine. There is no reason that a blending mode can't apply to > a different > >P-D operator. > > > >>I am tempted to split the spec, but keep the comp-op keyword the same > for both PD and blending. > > > >I think this is a mistake. We should split them. > > > >For example, I have two circles as part of a Venn diagram and I want to > apply a blend > >to their intersection - I can P-D 'src-in' the objects and apply > comp-op="overlay" or similar. > >The result of that is an area which has the 'overlay' applied to just the > intersection of > >the objects. > > > >I can't remember if 'Shake' was able to do that, but it did handle P-D > and blending IIRC. > > > >>This does imply that you won't be able to do xor or src-in with blended > content. Does anyone believe that this is a use case? > > > >Yes it's a use case. I think you'll find that sort of thing used in > high-end video editing etc, > > > > > >OK. Unless anyone objects, let's make them 2 separate properties. It is > cleaner that way. > > > >The 'comp-op' keyword will only apply to the PD blend modes. 'src-over' > will be the default. > >The 'blend' keyword will specify what blending mode to use. 'Normal' will > be the default. > > In ASV the blend keyword was 'adobe-blending-mode' and it handles all the > examples > in the spec dealing with blending if you go: > > s/comp-op/adobe-blending-mode/g > > in a text editor. > > So, I'd suggest 'blend-mode' or 'blending-mode' may be nicer. > OK. 'blend-mode' sounds better. > > Alex > > >Rik > > > > > > > > > >
Received on Wednesday, 9 November 2011 05:25:51 UTC