- From: Rik Cabanier <cabanier@gmail.com>
- Date: Tue, 22 Nov 2011 15:18:02 -0800
- To: Cyril Concolato <Cyril.Concolato@cisra.canon.com.au>
- Cc: Alex Danilo <alex@abbra.com>, "www-svg@w3.org" <www-svg@w3.org>, "public-fx@w3.org" <public-fx@w3.org>
- Message-ID: <CAGN7qDB9qDF=KpeE3Q-5F2xP=q12j7JbcSwGPZ+QxT_K4S4zdA@mail.gmail.com>
On Tue, Nov 22, 2011 at 1:50 PM, Cyril Concolato < Cyril.Concolato@cisra.canon.com.au> wrote: > Hi Alex, > > Thank you for your answer. See my comments below. > > -----Original Message----- > From: Alex Danilo [mailto:alex@abbra.com] > Sent: Tuesday, 22 November 2011 1:01 PM > To: www-svg@w3.org; public-fx@w3.org > Subject: RE: [css-compositing] some proposals > > -- > NB: Sorry for the spam www-svg (note to self: debug mailer agent;-( > -- > Hi Cyril & Rik, > > Sorry I've been a bit busy of late so following up now. > > First, one thing that's been missed is that in Porter-Duff the > alpha channel represents a mask. The crux of the original paper is > representing what happens with shape overlap on a pixel and so in the > compositing spec. we reproduce the 'square with 4 areas' > that has the top section multi-coloured, the left yellow, the right blue > and the bottom white. > > Those areas represent 0, A, B, and AB in the original P-D paper. > > In the spec. further down where it says: > "The operation used to place objects onto the background is as follows" > > there are these equations: > Dca' = f(Sc, Dc) × Sa × Da + Y × Sca × (1-Da) + Z × Dca × (1-Sa) > Da' = X × Sa × Da + Y × Sa × (1-Da) + Z × Da × (1-Sa) > > The Porter-Duff mode chosen affects X, Y, and Z. > > The blend mode is f(Sc, Dc). > [Cyril] So I understand that the proposal to split the modes into two > parts (P-D and blending) is purely syntactic sugar and it does not change > the model, right? > > So for example if you chose blend-mode:multiply, comp-op:src-in; > you would get: > > f(Sc,Dc) = Sc × Dc > X = 1 > Y = 0 > Z = 0 > [Cyril] According to the current draft: src-in is f(Sc,Dc)=Sc and X=1 and > Y=Z=0. Multiply is f(Sc,Dc)=Sc x Dc and X=Y=Z=1. So you are saying that > when you use both the compositing and the blending modes, you keep the > value of f(Sc,Dc) from the blending and you keep the X, Y, Z values from > the compositing mode. It make sense but it's not obvious. I would have > thought that you would somehow compose them. Anyway, I think that if we > split the spec, the merging of equation needs to be documented. > > The model is that you calculate the blended image first (= f(Sc, Dc)) and then composite it with whatever mode was specified. The current spec always assumes that you do src-over with blending and that is changing. So in the new spec: - multiply becomes f(Sc,Dc)=Sc x Dc (no more x, y, z) - src-in becomes X=1, Y=Z=0 (no more f(Sc, Dc)) Rik
Received on Tuesday, 22 November 2011 23:18:33 UTC