Dear Jeremy, Thanks! Just a follow-up... some software (e.g. pyFerret we use) uses overlapping pixels to avoid aliasing effects; surprisingly, it works. A requirement is that all pixels should be present (no holes). Nonetheless, one cannot use transparency here at all.
I do not believe that setting higher DPI will fix the colour problem though. I do suspect that colour coding may not match, or there is a bug with transparency setting (e.g., https://github.com/OpenOrienteering/mapper/issues/482 ). Something similar is spotted in another Qt-based application (https://hub.qgis.org/issues/4641 )/. Indeed, it may be a ticked on Qt's PDF export. All the best, Serge > -----Original Message----- > From: Jeremy Sanders [mailto:[email protected]] > Sent: 12 May 2016 19:16 > To: Gromov, Sergey <[email protected]>; Michael Clerx > <[email protected]>; [email protected] > Subject: Re: [Veusz-discuss] Image to pdf conversion > > Hi all > > Interesting - I've seen the smoothing in SVG. I don't think there's any way to > switch it off in the file format. I don't think there are options to disable > compression Qt's PDF export. I should file a bug report about the Pdf, as I > don't > think it's the correct default behaviour (if anyone else has time please feel > free to > do this). > > As you suggest, using rectangles mostly works, though in practice, you get > annoying light lines between the rectangles due to anti-aliasing in PDF > viewers, > etc. > > One solution is to resample the image to a higher resolution - this should > reduce > the effect of the smoothing and the compression. In fact the default image > widget will do this if the image x and y grid is not regular. The downside is > the > extra space used in the output file. > > So Michael, you could try making the 2D dataset slightly irregular in its > gridding. > This should force veusz to resample the image to higher resolution. I can't > remember how it chooses the resampled image size, but I think it takes the > smallest difference between bin widths and resamples to that (with some > limit). > > I should add an option to resample to XXX DPI. > > Chers > > Jeremy > > On 05/12/2016 12:23 PM, Gromov, Sergey wrote: > > Hi all, > > > > I have the same issue on Windows, up to the latest version. > > My guess it has to do with extensive bitmap compression (it looks like jpg > > with > colour compression), through which the colours indeed change sometimes > substantially (read I cannot use this PDF for publication). SVG blurs the > bitmap, > which is also bad. > > See the example (pdf vs. png vs. svg) attached. > > > > I wonder if it is possible to produce PDFs with bitmaps replaced with > > primitives > (i.e. matrices of boxes) of given colour... I did this trick when I had to > produce a > vector output with image, i.e. reading the matrix and plotting it as 'xy' > with given > coordinates and square symbol emulating pixels. But that is usually a lot of > work... > > > > Sergey > > > > > >> -----Original Message----- > >> From: Veusz-discuss [mailto:[email protected]] On Behalf > >> Of Jeremy Sanders > >> Sent: 12 May 2016 10:31 > >> To: Michael Clerx <[email protected]>; [email protected] > >> Subject: Re: [Veusz-discuss] Image to pdf conversion > >> > >> On 11/05/16 23:24, Michael Clerx wrote: > >> > >>> I've used Veusz to create some nice 2d-density plots using the "image" > >>> widget. > >>> However, when I export my graph to PDF the colours change considerably. > >>> I'm using the bluegreen colormap (inverted). > >>> > >>> Has anybody else experienced similar problems? > >> > >> I don't see the problem with the mandelbrot example with bluegreen on > >> linux, after exporting to PDF. There is some smoothing introduced, > >> but the colours look ok. > >> > >> What version and platform are you using? > >> > >> Thanks > >> > >> Jeremy > >> > >> > >> _______________________________________________ > >> Veusz-discuss mailing list > >> [email protected] > >> https://mail.gna.org/listinfo/veusz-discuss > >> > >> > >> _______________________________________________ > >> Veusz-discuss mailing list > >> [email protected] > >> https://mail.gna.org/listinfo/veusz-discuss _______________________________________________ Veusz-discuss mailing list [email protected] https://mail.gna.org/listinfo/veusz-discuss
