R devel - Nov 2015 - PDFs and SVGs containing rasterGrobs don't display correctly in some other software

I've just been trying to post-process some R-created heatmaps using
Inkscape, but I can't get them to display correctly in that software.

To reproduce:

library(grid)
r <- as.raster(matrix(runif(25), 5, 5))
pdf("test.pdf")
grid.newpage()
grid.raster(r, interpolate = FALSE)
dev.off()

This figure should be a five by five block of grey squares.  This is
what I see in the R GUI device window, and when I open test.pdf in
Abode Reader or SumatraPDF.

However, when I open the file in Inkscape or Firefox, each of the
squares is blurred.

I tried swapping grDevices::pdf for Cairo::CairoPDF and got the same
result.  I also tried generating SVGs using both grDevices::svg and
Cairo::CairoSVG, and also got the same result.

I see the same thing using R-devel and R3.2.2 under Windows, and (with
an older version of R) under Linux.

I don't know whether the problem is with grid's rasterGrobs, or how R
writes PDF and SVG files, or with Inkscape and Firefox's method of
rendering those files, or with me.  Please can you help me narrow it
down.

- Can you reproduce my problem?  That is, when you run the above code,
does the file look OK in a PDF reader but blurry in Inkscape?
- Do you know of any issues with using rasterGrobs in PDFs or SVGs?

-- 
Regards,
Richie

Learning R
4dpiecharts.com

On Thu, Nov 5, 2015 at 5:43 AM, Richard Cotton <richierocks at gmail.com>
wrote:
> I've just been trying to post-process some R-created heatmaps using
> Inkscape, but I can't get them to display correctly in that software.
>
> To reproduce:
>
> library(grid)
> r <- as.raster(matrix(runif(25), 5, 5))
> pdf("test.pdf")
> grid.newpage()
> grid.raster(r, interpolate = FALSE)
> dev.off()
>
> This figure should be a five by five block of grey squares.  This is
> what I see in the R GUI device window, and when I open test.pdf in
> Abode Reader or SumatraPDF.
>
> However, when I open the file in Inkscape or Firefox, each of the
> squares is blurred.
>
> I tried swapping grDevices::pdf for Cairo::CairoPDF and got the same
> result.  I also tried generating SVGs using both grDevices::svg and
> Cairo::CairoSVG, and also got the same result.
>
> I see the same thing using R-devel and R3.2.2 under Windows, and (with
> an older version of R) under Linux.
>
> I don't know whether the problem is with grid's rasterGrobs, or how
R
> writes PDF and SVG files, or with Inkscape and Firefox's method of
> rendering those files, or with me.  Please can you help me narrow it
> down.
>
> - Can you reproduce my problem?  That is, when you run the above code,
> does the file look OK in a PDF reader but blurry in Inkscape?
> - Do you know of any issues with using rasterGrobs in PDFs or SVGs?
Yes - many viewers (esp. OS X preview) interpolate them even when the
PDF requests that they shouldn't be. I worked through this with Paul
Murrell a couple of months ago - we're reasonably certain that R is
doing the right thing, it's the renderers that are failing.

Hadley

-- 
http://had.co.nz/

On Nov 5, 2015 03:45, "Richard Cotton" <richierocks at
gmail.com> wrote:
>
> I've just been trying to post-process some R-created heatmaps using
> Inkscape, but I can't get them to display correctly in that software.
>
> To reproduce:
>
> library(grid)
> r <- as.raster(matrix(runif(25), 5, 5))
> pdf("test.pdf")
> grid.newpage()
> grid.raster(r, interpolate = FALSE)
> dev.off()
>
> This figure should be a five by five block of grey squares.  This is
> what I see in the R GUI device window, and when I open test.pdf in
> Abode Reader or SumatraPDF.
>
> However, when I open the file in Inkscape or Firefox, each of the
> squares is blurred.
Not sure if it's related to how PNGs are rendered in Firefox, but it sounds
similar to the anti-aliasing used by Firefox when scaling up PNGs:

http://stackoverflow.com/questions/388492/firefox-blurs-an-image-when-scaled-through-external-css-or-inline-style

Firefox made anti-aliasing ("blurring") the new default many years
ago.
After complaints they provided a way to control this behavior via (a
Mozilla-specific) CSS specification.  See above thread (which is wire old;
there might be more up-to-date reference out there).

If you output a PNG and insert it in a HTML img where you scale up the
width and height, do you see the same problem in Inkscape as in Firefox?
>
> I tried swapping grDevices::pdf for Cairo::CairoPDF and got the same
> result.  I also tried generating SVGs using both grDevices::svg and
> Cairo::CairoSVG, and also got the same result.
If you inspect your generated SVG, is the raster image embedded as a PNG?
Then SVG is unlikely to change the rendering property compared PNGs
(sic!).  However, you might be able to control the anti-aliasing property
of embedded rather images in SVGs using embedded CSS if you want a
self-contained SVG file that renders properly everywhere. You can also do a
self-contained HTML in a similar way.

Don't know if there exist a workaround for PDFs (didn't even know about
it
until you mentioned it).

My $.02

Henrik
(from smartphone so sorry for typos etc)
>
> I see the same thing using R-devel and R3.2.2 under Windows, and (with
> an older version of R) under Linux.
>
> I don't know whether the problem is with grid's rasterGrobs, or how
R
> writes PDF and SVG files, or with Inkscape and Firefox's method of
> rendering those files, or with me.  Please can you help me narrow it
> down.
>
> - Can you reproduce my problem?  That is, when you run the above code,
> does the file look OK in a PDF reader but blurry in Inkscape?
> - Do you know of any issues with using rasterGrobs in PDFs or SVGs?
>
> --
> Regards,
> Richie
>
> Learning R
> 4dpiecharts.com
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
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