[luatex] luatex doesn't set /Smask in pdf 2.0

Ulrike Fischer luatex at nililand.de
Wed Jun 30 15:01:39 CEST 2021


I lost transparency in a png used in a pdf 2.0 document. 

It looks as if luatex decides if to use a /Smask by looking only at
the minor version. So 1.4-1.9 work, 2.0-2.3 fail, 2.4 works again


\pdfvariable compresslevel=0
\pdfvariable objcompresslevel=0
\pdfvariable majorversion =2
\pdfvariable minorversion =0 % or 4
\saveimageresource {transparent.png}
\useimageresource\lastsavedimageresourceindex
xxx
\bye

Result 

minor 0:
<< /Type /XObject /Subtype /Image /Width 50 /Height 50
/BitsPerComponent 8 /ColorSpace /DeviceRGB /Length 7500 >>

minor 4:
<< /Type /XObject /Subtype /Image /Width 50 /Height 50
/BitsPerComponent 8 /ColorSpace /DeviceRGB /SMask 7 0 R /Length 7500
>>

transparent.png is an arbitrary image with transparency. 


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



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