[luatex] png inclusion differs luatex vs pdftex

[Ulrike Fischer]

Am Tue, 30 Apr 2024 11:00:44 +0300 schrieb Linas Stonys:

> I get different colors of png image (attached europe.png) when I 
> compile  lualatex and pdfflatex.
> Image contains some "transparency group".
> Differences are seen in acrobat but pdfxchange and sumatra shows the 
> same (normaly like pdflatex did)

> Could luatex load png  like pdftex does?

You can add the Group key to the current page with

\pdfvariable pageattr{/Group <</S /Transparency /I true /CS
DeviceRGB>>}

or if you use the LaTeX pdfmanagement (with \DocumentMetadata{})
with 

\ExplSyntaxOn
\pdfmanagement_add:nnn{ThisPage}{Group}{<</S /Transparency /I~true
/CS /DeviceRGB>>}
\ExplSyntaxOff

pdftex adds that automatically if it detects a png with
transparency, but on the whole I prefer the luatex method, as there
is less danger that you end up with duplicated Group entries.

BTW: Adobe reader only shows a difference if you have set in the
preferences -> page display "Use overprint preview" to "always" or
to "automatic". 

-- 
Ulrike Fischer 
http://www.troubleshooting-tex.de/