[tlbuild] writepng.c: No transparency with PDF/A-1b

[Martin Schröder]

2014/1/7 Florian Breitwieser <florian.bw at gmail.com>:
> I am trying to create PDF/A-1b compliant documents with (pdf)LaTeX.
> PDF/A-1 is based on PDF v4, however unlike the former it does not
> allow transparency (and is very strict about all its rules).
>
> ./texk/web2c/pdftexdir/writepng.c only writes the alpha channel when
> pdfminorversion is >= 4, and excludes it otherwise. Eg in line 523:
>
>     /* alpha channel support */
>     if (fixedpdfminorversion < 4
>         && png_get_color_type(png_ptr(img), png_info(img)) |
> PNG_COLOR_MASK_ALPHA) {
>         png_set_strip_alpha(png_ptr(img));
>         png_copy = false;
>     }
>
> Would it be feasible to add a 'notransparency' or 'pdfa1' flag to
> generate a no-transparency PDF 4 document?

AFAIK it's based on 1.3 (the main addition of 1.4 is transparency),
so can't you just set pdfminorversion to 3?

Best
   Martin

PS: Crossposted to the pdftex-devel list