[R] gray background in png

[Deepayan Sarkar]

On Sunday 18 July 2004 10:29, Liaw, Andy wrote:
> Seems like a bug to me.  I tried setting theme=col.whitebg in
> arguments to trellis.device, same result.  Setting
> options(lattice.theme=col.whitebg) also does the same thing.  The
> same thing happens win.metafile() for me. This is on WinXPPro,
> R-1.9.1 and

Definitely a bug, but probably not where you would think. Note that 
col.whitebg() is misnamed, the background is actually  'transparent'. 
As far as I can make out, the first plot is the one that's wrong, all 
the subsequent ones are fine. (The apparent 'grayness' of the 
background is probably just a feature of your png displayer.) 

The workaround depends on whether you really want a white or transparent 
background.


For transparent:

library(lattice)
z <- expand.grid(A = LETTERS[1:8], B = letters[1:6], x = 1, y = 1)

trellis.device(png, file = "test%02d.png")
par(bg = "transparent")
lset(col.whitebg())

xyplot(y ~ x | A * B, data = z, layout = c(4, 6))
dev.off()


For white:

library(lattice)
z <- expand.grid(A = LETTERS[1:8], B = letters[1:6], x = 1, y = 1)

trellis.device(png, file = "test%02d.png") 
par(bg = "white")
lset(col.whitebg())
lset(list(background = list(col = "white")))

xyplot(y ~ x | A * B, data = z, layout = c(4, 6))
dev.off()


The reason for this, I think, is that grid seems to use par("bg") for 
the background of the first plot, but not for the rest. See, for 
example. the results of 

png(bg = "yellow")
grid.lines()
grid.newpage()
grid.lines()
dev.off()

I'll have to think about the best way to fix this. 

Deepayan