[Rd] Use cairo fallback resolution greater than 72dpi in cairo_pdf and cairo_ps in grDevices

[Prof Brian Ripley]

On 18/07/2015 09:09, Prof Brian Ripley wrote:
> The 'at a minimum' information requested by the posting guide is missing.
>
> According to their documentation the cairo default fallback resolution
> is now 300dpi, and when I run your example on Fedora 21 that is what the
> emitted postscript says it is.
>
> You can easily alter the R code to set it to something different: see
> http://cairographics.org/manual/cairo-cairo-surface-t.html for the call
> you would need to add.

I've added the ability to set the fallback resolution in R-devel, mainly 
because it seems to be system-specific (I still recommend using a bitmap 
format such as PNG directly).

>
> However, I would suggest that you generate a bitmap directly and use
> that, as PostScript does not support semi-transparency.
>
> On 14/07/2015 12:03, Tom Wenseleers wrote:
>> Dear all,
>> In grDevices R functions cairo_pdf and cairo_ps it is mentioned that
>> when transparency (alpha channels) are used in vector output, it will
>> rasterize the PDF or postscript exported graph at a resolution of 72
>> dpi :
>> https://stat.ethz.ch/R-manual/R-devel/library/grDevices/html/cairo.html
>>
>> You can see the problem if you try
>>
>> library(ggplot2)
>> cairo_ps(file = "test.eps",onefile = FALSE)
>> qplot(Sepal.Length, Petal.Length, data = iris, color = Species, size =
>> Petal.Width, alpha = I(0.7))
>> dev.off()
>>
>> as in the output (here zoomed in) the plot symbols are heavily
>> pixelated then, showing it is only using 72 dpi.
>>
>> I was wondering how the fallback resolution could be increased to 600
>> dpi? In library(RGtk2) there is a command
>> cairoSurfaceSetFallbackResolution, which I think is what is relevant
>> here, but I would not know how to make grDevices use that parameter.
>> Any thoughts?
>>
>> Using postscript() btw also doesn't work, since that doesn't support
>> transparency, and returns the error "semi-transparency is not
>> supported on this device: reported only once per page".
>>
>>
>> I know I can use svg or pdf instead and that this would solve the
>> problem, but problem is the journal (PloS) I would like to submit to
>> only accepts EPS. So is there any solution to increase the quality in
>> EPS, without having to rasterize everything to PNG?
>>
>> best regards,
>> Tom Wenseleers
>>
>>
>>
>>
>>
>>
>>     [[alternative HTML version deleted]]
>>
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>>
>
>


-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Emeritus Professor of Applied Statistics, University of Oxford
1 South Parks Road, Oxford OX1 3TG, UK