R help - Mar 2007 - alpha parameter in function rgb to specify color

Hi All, 

In function "rgb", alpha parameter is supposed to set
the transparency value. But in my following two
examples, it didn't work:

plot(1,col = rgb(1,0,0,alpha =0.8))
# as long as alpha < 1, there is no point in the plot.

plot(1,col = rgb(0,0,255, alpha=254,
maxColorValue=255))
# as long as alpha < 255, there is no point in the
plot. 

Do I use it in the right way? Any advice is
appreciated. 

Best,

Jun Ding


 
____________________________________________________________________________________
Expecting? Get great news right away with email Auto-Check.

Which graphics device are you using?

________________________________

From: r-help-bounces@stat.math.ethz.ch on behalf of Jun Ding
Sent: Wed 3/7/2007 9:47 PM
To: r-help@stat.math.ethz.ch
Subject: [R] alpha parameter in function rgb to specify color



Hi All,

In function "rgb", alpha parameter is supposed to set
the transparency value. But in my following two
examples, it didn't work:

plot(1,col = rgb(1,0,0,alpha =0.8))
# as long as alpha < 1, there is no point in the plot.

plot(1,col = rgb(0,0,255, alpha=254,
maxColorValue=255))
# as long as alpha < 255, there is no point in the
plot.

Do I use it in the right way? Any advice is
appreciated.

Best,

Jun Ding



____________________________________________________________________________________
Expecting? Get great news right away with email Auto-Check.

______________________________________________
R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.



	[[alternative HTML version deleted]]

Part of the problem is that alpha is a new and undocumented feature 
(note to developers: add this info into the pdf and rgb documentation). 
It only works in PDFs (maybe on quartz on Macs?), so you need to write 
to a PDF file:

pdf("out.pdf",version="1.4")
plot(1:10,col=rgb(1,0,0,alpha=seq(0,1,length.out=10)))
dev.off()

Now open up the PDF file...