[R] Q: obtaining non-transparent background in png

[Gavin Simpson]

On Tue, 2007-07-31 at 10:22 -0600, D. R. Evans wrote:
> I am not understanding something about generating PNG plots.
> 
> I have tried several ways to obtain something other than a transparent
> background, but nothing I've done seems to change the background.
> 
> For example:
> 
> dev.print(png, width=800, height=600, bg='red', filename='example.png')
> 
> which I thought would give a red background, simply gives the same
> transparent background I always get.

?dev.print says:

     'dev.print' copies the graphics contents of the current device to
     a new device which has been created by the function specified by
     'device' and then shuts the new device.

Note "copies" - given that you've already drawn a figure with a white
background, should this then produce one that is red? However, you are
correct that it does produce a plot with a transparent background.

I find it easier to wrap my plotting commands in the relevant device,
e.g. this works with the desired background:

> png("mypng.png", height = 400, width = 400, bg = "red", 
      pointsize = 12)
> plot(1:10)
> dev.off()

Whereas these do not give "red" backgrounds as one might have expected,
but transparent ones:

> plot(1:10)
> dev.print(png, height = 400, width = 400, bg = "red", pointsize = 12, 
            filename = "mypng2.png")
X11
  2
> dev.copy(png, height = 400, width = 400, bg = "red", pointsize = 12, 
           filename = "mypng3.png")
PNG
  3
> dev.off()
X11
  2

Not sure whether this is as intentional or not, but it does not appear
to be passing the bg argument on to the 'device', or if it does, it is
not being used/respected - perhaps all that is need is clarification as
to what can be specified in '...' in ?dev.print

> version
               _
platform       i686-pc-linux-gnu
arch           i686
os             linux-gnu
system         i686, linux-gnu
status         Patched
major          2
minor          5.1
year           2007
month          07
day            05
svn rev        42131
language       R
version.string R version 2.5.1 Patched (2007-07-05 r42131)

G

> 
> And I also don't understand why the default background is transparent,
> when the documentation seems to say that it's white:
>   png(filename = "Rplot%03d.png", width = 480, height = 480,
>          pointsize = 12, bg = "white",  res = NA,...)
> 
> (This is on a Kubuntu dapper 64-bit system.)
> 
> [I looked through the mail archives, and there seem to be a few very
> old postings talking about the opposite problem, but nothing recent;
> so I conclude that I'm doing something wrong.]
> 
> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
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