Re: minutes, SVG WG Seattle F2F 2011 day 3 - SVG Color

2011/8/2 Alex Danilo <alex@abbra.com>

> Hi All,
>
>        I have a couple of comments about the auto black
> switching stuff.
>
>        Anyway, as far as black preservation goes - this does
> need to be specified and preserved through the render engine.
>
>        It is quite common in printing to preserve black for an
> object even if it's overlayed with transparent things on top.
> So the example in the minutes with a gradient on top of a black
> object could still retain the full black channel underneath.
>

I agree.If you look how InDesign handles CMYK, it almost never touches them
when you go to output.
In 99.9% of all cases, designers don't want the application to touch their
CMYK.

Transparency does introduce some interesting problems.
Maybe the minutes weren't complete. What we discussed was a black box that
was transparent on top of a color managed image.
In that case, the black box really becomes filled with an darkened image and
might not follow black preservation rules.


>
>        This is done primarily for bleed/registration at the edges
> of objects such as glyphs, etc. The end result is that you have a mix
> of CMY as well as black in a channel (no under colour removal).
> So it's not uncommon to see something like (30%, 30%, 30%, 100%)
> for the CMYK channels. None of this matters for screen/pixel
> scenarios but is essential on any RIP used for printing.
>
>        The spot/named colour case is another where this kind of
> thing is mandated.
>

definitely. Spot colors need to be maintained as separate channels through
the pipeline, not just their CMYK values.


>
>        The upshot of this is that the objects do need to be
> tagged at the input, you can't do it automatically. All RIPs
> used in typesetting do this one way or another. So if we're
> going to let SVG be used for print workflows the colour
> management model needs beefing up.
>

There is a movement to not do this in the RIPs but upstream, either in your
publishing apps (like InDesign) or your document workflow system (like
AGFA's Apogee).


>
>        Don't know that these comments add much, but the printing
> people that care may want to add some RIP compatible suggestions
> so someone one day will stick native SVG in a printer...
>
> Alex
>
> --Original Message--:
> >No, the profile on the image is correct. I want the image to use rich
> black. That way any gradient in the image (the example image doesn’t really
> have one, but imagine a picture that fades to black on the edges) is nice
> and continuous.
> >
> >Therefore, if I put the image on a black background or want to put a black
> border on it, I want that black to be rich black as well.
> >
> >If we’re going to decide automatically that all solid filled black (and
> presumably gray) shapes and strokes will use preserve-black, this isn’t
> going to happen.
> >
> >That’s why I think we need an extra switch for the preserve black option.
> >
> >Lcms2 added this extra option (no-preservation, black only, black-plane)
> by duplicating its intents, but an optional switch seems cleaner to me. (
> http://sourceforge.net/apps/trac/mpc-hc/browser/trunk/src/thirdparty/lcms2/src/cmscnvrt.c?rev=3024see DefaultIntents[])
> >
> >
> >Nick Hofstede
> >
> >R&D Manager
> >
> >From: Rik Cabanier [mailto:cabanier@gmail.com]
> >Sent: maandag 1 augustus 2011 19:26
> >To: Nick Hofstede
> >Cc: www-svg@w3.org
> >Subject: Re: minutes, SVG WG Seattle F2F 2011 day 3 - SVG Color
> >
> >
> >Hi Nick,
> >
> >
> >I think this is a case where you want to ignore the profile that is
> attached to the image and swap it out with the destination profile instead.
> >
> >
> >There was a discussion at the f2f why we would need to swap out the
> attached profile. This seems to be a valid use-case for such a feature.
> >
> >
> >Rik Cabanier
> >
> >
> >On Mon, Aug 1, 2011 at 12:07 AM, Nick Hofstede <
> Nick.Hofstede@inventivegroup.com> wrote:
> >
> >Quick note on the black preservation:
> >
> >  ChrisL: last issue is preserving black.
> >  ... For example, in ICC if you specify cmyk(0,0,0,1),
> >  color-management systems tend to have a switch that specially treats
> >  that value.
> >  ... So even if the system does color-manipulation normally, that one
> >  color will instead stay solid, total black.
> >  ... This is so black text stays pure black and doesn't mix in other
> >  colors.
> >  ... So, similarly, we need to see if we need it, and see if it's an
> >  input or output feature.
> >
> >  cabanier: We have it in InDesign, and it's an output feature there.
> >  ... So we have some special cases there again; you don't want to
> >  preserve black on an image.
> >
> >  ChrisL: So that's basically actually being an input feature.
> >
> >  heycam: Does it make sense to have this controllable on images, or
> >  if we can magically just apply it to solid-color fills and strokes?
> >  ... Also, if you have some colored shapes which are composited
> >  together, and you happen to get black out of that, should that be
> >  preservable?
> >
> >  TabAtkins_: So it sounds like we can just specify that solid-color
> >  strokes and fills automatically preserve black, and nothing else
> >  does. It can be applied on output, and doesn't need to be specified
> >  on input.
> >
> >  cabanier: So we look at the operator on printing - if a shape is
> >  filled with an image or gradient, we don't preserve black. If it's
> >  filled with a color, we preserve.
> >
> >  TabAtkins_: So if you composite a partially-transparent gradient
> >  over a black rectangle, you wouldn't preserve the black in it.
> >
> >  heycam: So basically, for any image, track if the result color comes
> >  partially from a gradient or image. If so, don't preserve black;
> >  otherwise, preserve it.
> >
> >  TabAtkins_: So it sounds like we can do this automatically at the
> >  end, and thus don't need a property for it.
> >
> >  heycam: And in PDF, it's not controllable; it just happens
> >  automatically.
> >
> >I'm not sure automatically deciding when to use black preservation is a
> good idea. I don't think you can always deduce it automatically and I think
> you should therefore be able to specify it.
> >Consider the use case talked about here for example:
> >
> http://www.blog.spoongraphics.co.uk/articles/the-ultimate-guide-to-designing-with-black
> >If you would create this in SVG your underlying rectangle would become
> black-preserved black, and the black from the image would be rich black.
> >You're going to want to be able to trigger rich black on the solid-color
> fill.
> >
> >With kind regards,
> >
> >Nick Hofstede
> >
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