út 26. 5. 2020 v 1:50 odesílatel Ross Moore <ross.mo...@mq.edu.au> napsal:
> Hi Zdenek, > > On 26 May 2020, at 9:31 am, Zdenek Wagner <zdenek.wag...@gmail.com> wrote: > > út 26. 5. 2020 v 0:59 odesílatel Ross Moore <ross.mo...@mq.edu.au> napsal: > >> and at the time, that appeared to solve my problem. However, it would >> appear that since then "xdvipdfmx" has been enhanced to support >> transparency, as a result of which Khaled's suggested FFFFFF00 no longer >> works (the text is invisible, see attached). Could anyone tell me how, >> short of using \specials, I can achieve 100% white with 100% opacity (= 0% >> ink) in XeTeX ? >> >> >> I’m sorry, but this just doesn’t make any sense to me — but see further >> below. >> Surely 100% opacity means that the blend between background and >> foreground is 100% background, 0% foreground. >> Thus your text will be invisible, whatever colour has been specified; >> that this is white becomes irrelevant. >> >> The only way to get 100% white, over a coloured background, would be with >> 100% ink, so 0% opacity. >> Any other opacity level will allow some of the background colour to be >> mixed in. >> At least that is how I understand what colour mixing is all about. >> >> Sorry, correct me if my English is wrong but I would expect 100% ink = > 100% opacity = 0% transparency > > > You’re absolutely correct, my mistake. > Certainly I meant 0% *transparency*, the opposite of what Phil was trying > to do. > It was he who said 100% opacity (= 0% ink) which is where the error > lies. > Surely 100% ink = 100% opacity = 0% transparency, as you say. > > >> However, there is another PDF parameter called “knockout”. >> See this link for an brief description of the issue: >> >> >> https://www.enfocus.com/en/products/pitstop-pro/pdf-editing/knockout-white-text-in-a-pdf >> <https://protect-au.mimecast.com/s/tuWYCBNqgBCvBNrAuzR3NV?domain=enfocus.com> >> > > This is another topic. This addresses "black overprint" in printing. > > > Sure, but it is about knocking out the colour in the background. > Using black text is probably its most common usage. > But if you want the natural paper to come through, then surely this is the > only way to do it conveniently. > > Otherwise you would have to manually define regions outlining the letters, > and make these > boundary curves for your background. Totally impractical. > PDF does this for you, if you have used the correct way to ask for it. > > Yes, I know, but knocking out works always while overprint requires CMYK. The colour of an OpenType font can only be specified in RGBA. > > The idea is that process colours are printed in the following order: > cyan-magenta-yellow-black. If you want to print a yellow text on a cyan > background, RIP must erase the cyan plate to white where the characters > will later appear on the yellow plate, otherwise the text would not be > yellow. If the offset films are not precisely adjusted, you will see colour > artifacts at the boarders of the characters. If you want to type a dark > text (usually black) to a light background, it can just be overprinted. In > order to make it work, both colours must be defined in CMYK (not RGB, not > grayscale). Professional Acrobat since version 9 contains a prepress > checking function which can verify whether overprint was really used. Black > overprint is implemented in my zwpagelayout package. It was tested in > xelatex, pdflatex, and latex + dvips. The package does not my test files. > If you like, I can send them. > > > Sure; I’d love to see these. > I’m sure that this would most closely approach what Phil seems to want to > do. > > I will send in in the next mail. > > > Zdeněk Wagner > http://ttsm.icpf.cas.cz/team/wagner.shtml > http://icebearsoft.euweb.cz > > > > >> How to achieve knockout using TeX+gs or pdfTeX or XeTeX? >> I’m not at all sure. It must have a graphics state parameter. >> The next image shows what I think is the relevant portion of the PDF >> specs. >> >> <Screen Shot 2020-05-26 at 8.38.02 am.png> >> >> There’s a whole section on “Transparency Groups”, but mostly it is about >> how different transparent objects >> must combine to produce the final colour where objects overlap. >> > > Transparency should not be used for prepress. It works fine on office > printers but often come out as black on phototypesetters and CTP. > > > Phil hasn’t said what is his application. > > After a cursory look, I think you need to use a Form X Object, which can >> be done in pdftex using the \pdfxform primitive, >> with appropriate attributes specified. >> For XeTeX you would need to be using \special commands. >> Someone here must have some experience with this. >> >> > Zdeněk Wagner > http://ttsm.icpf.cas.cz/team/wagner.shtml > <https://protect-au.mimecast.com/s/TZFICD1vRkCX0ZzMs5cgKz?domain=ttsm.icpf.cas.cz> > http://icebearsoft.euweb.cz > <https://protect-au.mimecast.com/s/4H07CE8wlRCBMj2nhptby5?domain=icebearsoft.euweb.cz> > > > > >> >> Philip Taylor >> <Demo.pdf><Demo.tex><Lighter ground.pdf> >> >> > > Sorry for my error adding to confusion. > > Cheers. > Stay safe. > > Ross > > > Dr Ross Moore > Department of Mathematics and Statistics > 12 Wally’s Walk, Level 7, Room 734 > Macquarie University, NSW 2109, Australia > T: +61 2 9850 8955 | F: +61 2 9850 8114 > M:+61 407 288 255 | E: ross.mo...@mq.edu.au > http://www.maths.mq.edu.au > > CRICOS Provider Number 00002J. Think before you print. > Please consider the environment before printing this email. > > This message is intended for the addressee named and may > contain confidential information. If you are not the intended > recipient, please delete it and notify the sender. Views expressed > in this message are those of the individual sender, and are not > necessarily the views of Macquarie University. <http://mq.edu.au/> > <http://mq.edu.au/> > >
