Inkscape

Display and Cairo export rendering mismatch with transparent objects

Asked by stationary

Hi Inkscape people!

I've been trying to create a design that ultimately will be sent to the printers, and this design uses transparent bitmaps to add a bit of texture. I'm finding that Inkscape's drawing area and the Export Bitmap's PNG agree in appearance, but saving as a Cairo PNG or a PDF gives really obviously different results that ruin any visual balance of transparency achieved within the Inkscape drawing area. I'm using Inkscape 0.46+devel r21524, built Jun 9 2009.

Also, loading the Inkscape SVG into Scribus 1.3.5svn gives more prominent transparency effects just like the Cairo exports.

I've got a test case SVG file here (embedded texture - 1.8MB): http://www.cognilab.co.uk/inkscape_rendering/test_case.svg

And a comparison of the different outputs here (0.8MB): http://www.cognilab.co.uk/inkscape_rendering/comparison_screenshot.png

The texture overlays the whole area with a transparency value of 50% and becomes far more prominent (though noticably still transparent) once passed through Cairo PNG or PDF export filters. Can a nice Inkscape developer out there please confirm and explain this behaviour, and offer a possible workaround or advice?

Thanks very much!

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pbhj (pbhj) said : 		#1

I'm not a dev, sorry.

It looks like the Cairo PNG and PDF are rendering at about 75% the overlay. I think this is actually your problem. Why can't you just use the normal (correctly rendered) exported PNG for the print? It can be embedded in a PNG file but there's no real reason why the printer can't use it except lack of technical expertise on their behalf, IMO.

Interestingly my file manager preview (Dolphin, KDE4) and Firefox 3.0.11 render the SVG file as in the "wrong" renderings. Strange.

Fixing, well as it's the opacity that there's a problem with if you create your plasma (in The GIMP?) with the opacity you need and then in Inkscape display it as 100% O then it should work in PDFs (does for me) and I guess in Cairo PNG too. An alternate is to do a bitmap copy which will semi-flatten the plasma overlay (making the Inkscape opacity 100% and folding the opacity into the PNG bitmap copy itself).

Excellently asked question - wish everyone asked so well!

HTH.

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