One problem with the TransPDF filter (Windows), which I also used to experience
with !OEPS when importing EPSs under RISC OS, is that the preview image
inevitably has a solid background (i.e. no alpha channel) even if the EPS/PDF
has a transparent background. If the EPS or PDF is placed in a transparent
frame it will print correctly to a Postscript device but be displayed
incorrectly on screen with a white background. Using built-in EPS previews this
is unavoidable. Using GhostScript to produce a preview for either EPSs or PDFs
a transparent background could be possible, because Ovation Pro correctly
displays transparent TIFFs, but GhostScript doesn’t produce TIFFs with an alpha
channel, hence the white background. However, it would produce PNGs with an
alpha channel, by changing '-sDEVICE= tiff24nc’ to '-sDEVICE=pngalpha’ (in the
second line of transpdf.txt). But of course Ovation Pro doesn’t display PNGs
directly, so it would be necessary to add an extra step to TransPDF then to
translate that PNG to a TIFF. That ought to be possible by whatever means the
TransPNG filter already uses to convert PNGs to TIFFs, except that the TransPNG
filter too ignores any alpha channel and also gives a white background.
Imagemagick (https://www.imagemagick.org ;<https://www.imagemagick.org/>) is a
superb utility for Linux/Windows/OS X which does everything (and far more) for
which one might use ChangeFSI on RISC OS. If it is installed in Windows
alongside Ghostscript (and the path to it perhaps included in transpdf.txt just
as the path to Ghostscript currently is) this could be done adding the simple
Imagemagick command ‘convert <previewfile.png> <previewfile.tif>’ to convert
the PNG output from the GhostScript command generated using the second line of
transpdf.txt to an alpha-channel TIFF to be used as the preview. And
similarly, Imagemagick could be used in TransPNG to make a better job of
importing PNGs than the present version does. (At present I always convert
TIFFs to PNG to avoid this problem.)
In fact, Imagemagick could be used for the first stage of making the TIFF
preview, anti-aliased and with transparency, directly from the PDF without
going via GhostScript. The equivalent to the GhostScript command generated by
line 2 of transpdf.txt, to convert the first page of a PDF to TIFF:
<ghostscriptpath>\gs -dSAFER -dBATCH -dNOPAUSE -sDEVICE=tiff24nc
-dTextAlphaBits=4 -dGraphicsAlphaBits=4 -sOutputFile=outfile.tif -r300 -q
-dFirstPage=1 -dLastPage=1 infile.pdf
(but anti-aliased and with an alpha channel if necessary, by default) would be:
<imagemagickpath>\convert -density 300 -depth 8 infile.pdf[0] outfile.tif
‘-depth 8’ seems to be necessary because otherwise it defaults to a
16-bits-per-channel (e.g. 48-bit RGB) TIFF which Ovation Pro will not handle.
That’s not necessary when converting from PNG to TIFF because by default it
preserves resolution and bit depth when converting between raster formats.
That produces a transparent TIFF which Ovation Pro displays correctly,
therefore ought to be suitable as a preview image for a PDF (or EPS).
This would be a better way than the present one to generate the TIFF preview
but GhostScript is still needed as before to convert from PDF to EPS for
printing because ImageMagick creates raster images only; although it will
output PDFs or EPSs they contain just a rasterised version of the input file.
Because the Ovation Pro filters are supplied as ready-built .exe files this is
not something I can experiment further with, unfortunately.
Peter.
