Hi David

Thank you for that detailed feedback!

At home I did a short test with CorelDraw X6 and transparent image areas.
Corel preserves the tranparent parts in the image, but the transition seems
harder and more like a sawtooth effect (due to the limitation of emf).

You can see the results in the contained zip file.

Best Regards
Eric




2015-02-09 19:14 GMT+01:00 David Mathog <email address hidden>:

> The short answer is that EMF does not support transparency very well.
>
> In modern bitmap formats one specifies for each pixel RGB and in
> addition a 4th value that sets the transparency.  In such a bitmap any
> color can have any transparency.  No EMF record type supports that.
> EMF format does support a more limited form of transparency where a
> regular RGB image is defined and in addition one color is set as
> "transparent".  This is essentially the same thing as "green screening"
> in a movie, that one color is completely transparent and all others are
> completely opaque.   (Note that EMF and WMF do support 4 byte/pixel
> bitmaps, but section 2.1.1.4 of the WMF manual says "The high byte in
> each DWORD is not used".  In theory one could extend the format in an
> incompatible manner by storing the usual transparency byte there.
> However, since that byte can legally have any value whatsoever, one
> would have to expect to run into images produced by other applications
> with that number of bytes/pixel which would import with spurious
> transparency values.)
>
> EMF has half a dozen "BLT" record types and the Inkscape implementation
> supports many of them, but not EMR_TRANSPARENTBLT, which is the one you
> would need for even the more limited "green screen" form of transparency.
> I will give this some thought - I guess it would be possible to scan the
> incoming image (from SVG) and IF all transparent pixels
> are 100% transparent AND they are the same color AND that color exists
> nowhere else in the image then we could use
> the EMR_TRANSPARENBLT format.  Going the other way would be trivial, but
> it has not come up before now, since nobody has yet posted an example
> generated by any other application that uses this record type.  I would not
> be surprised if we found that perfectly valid EMR_TRANSPARENTBLT records
> were imported poorly or not at all by other applications.
>
> The EMF output you are seeing does appear to be correct for the current
> implementation.   The transparent image does appear to have black pixels
> in the areas shown - but with an opacity of 0.
>
> It _should_ have been possible to work around this by defining a
> clipping region and clipping the image, however I see that doesn't work.
> This is very odd, since a clipped path type object works, but adding an
> image and clipping both the path and the image is broken.  I will look
> into that.
>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1419686
>
> Title:
>   emf-export renders transparent image areas black
>
> Status in Inkscape: A Vector Drawing Tool:
>   Confirmed
>
> Bug description:
>   The transparent parts of images become black when exported into the
> emf-format.
>   I am using Inkscape 0.91 on Windows 7; the emf-file is viewd in
> Microsoft Word 2010.
>
>   Included is a Inkscape test file plus the resulting emf file.
>
>   I consider the Inkscape emf export fare superior to Adobe Illustrator
> and are very glad about the new version.
>   Thanks for the great wok!
>
>   Best Regards
>   Erich
>
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