Re: CSS overprinting

On Wed, Jul 30, 2014 at 4:13 PM, Lea Verou <lea@verou.me> wrote:

> On Jul 31, 2014, at 01:59, Rik Cabanier <cabanier@gmail.com> wrote:
>
> On Wed, Jul 30, 2014 at 3:34 PM, Lea Verou <lea@verou.me> wrote:
>
>> Resurrecting this thread as no resolution has been reached, to mention
>> that AntennaHouse also has its own proprietary syntax for overprinting [1]
>
>
> A device dependent feature such as overprinting doesn't belong in CSS.
> Prepress workflows have the necessary logic to deal with automatically
> create overprinted colors depending on the colors, content used and
> transparency effects.
>
>
> Like it has already been mentioned in the thread, overprinting cannot
> always be determined algorithmically, and even when it could, it would be
> risky to assume that this is the intent in many cases.
>

Can you cite any examples where it can not be determined?
For those cases, could the same effect be produced by blending?


> Transparency has little to do with overprinting.
>

uhm, yes it does. Opacity and blending interact with overprinting.
See chapter 7.6.3 in the PDF reference manual [1] for the mess that this
creates. It's likely that nobody resolved all the problems in this area.


> For example, can you do [1][2] with alpha transparency (or anything else,
> really)?
> This is why every native app for print work has an overprint option
> (InDesign [3], Illustrator [4], etc),
>

Adobe applications routinely strip out the overprint from native and placed
content because it causes so many issues on output.

Note that you likely don't just want the old school overprint with deals
with CMYK and spot but instead want to tread the process colors as if they
were spot channels (So CMYK black overprints a CMYK color)


> and the most popular print formatters have proprietary syntax for it
> (Prince [5], AntennaHouse [6]). Do we want CSS to be able to compete with
> DTP apps or not? Cause I thought that being able to do serious print work
> with CSS *is* one of our goals, non?
>

Yes, eventually we want to do serious print work. This is why we should NOT
introduce overprinting since it was designed for a workflow that predates
opacity, filters and blending.
Let the postprocessors deal with this. They know best what colors they
output and the characteristics of the output device. They also determine
overprint AFTER opacity and blending is resolved so they can make the right
decision.

[1]:
http://blog.spoongraphics.co.uk/articles/how-to-overprint-colors-to-create-cool-print-effects
[2]:
http://blog.spoongraphics.co.uk/articles/showcase-of-designs-made-with-cool-overprint-effects
-> these examples only work if you print with spot or turn on OPP. The
output will look completely wrong when printing CMYK or viewing it in Apple
Preview

[3]: http://helpx.adobe.com/indesign/using/overprinting.html
-> notice all the warnings in this page

[4]:
http://help.adobe.com/en_US/illustrator/cs/using/WS714a382cdf7d304e7e07d0100196cbc5f-6495a.html
-> this page is really old

1:
http://wwwimages.adobe.com/content/dam/Adobe/en/devnet/pdf/pdfs/pdf_reference_archives/PDFReference15_v5.pdf