R help - Jan 2009 - Problem with cex=0.1 when making jpegs

I am using the following script to make .jpg files. 

jpeg('plotx.jpg')

ddat <-read.table("file",header=T)
attach(ddat)
tdat<-read.table("file1")
plot(xx1,yy1,type='p',pch=1,col="blue",cex=0.2,xlim=c(0,3.5),ylim=c(-75,75))
points(tdat,col="green",pch=1,cex=0.2)

dev.off()

The problem is that I want the points to be very small; however, if I make
cex any smaller than 0.2 the plot in the .jpg file is blank. If I run the
commands from the console (on a Mac) - with the exception of jpeg() and
dev.off() then it works even if cex < 0.2. I've tried making .ps files
and
converting to .jpg but then I run into different problems with the animation
software (imageJ).

Thanks for any suggestions
-- 
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Looking at ?points I see information that appears directed at this  
question:

Value pch="." (equivalently pch = 46) is handled specially. It is a  
rectangle of side 0.01 inch (scaled by cex). In addition, if cex = 1  
(the default), each side is at least one pixel (1/72 inch on the pdf,  
postscript and xfig devices).

The points appear with plot(1:10, pch = ".", cex=1)

I can still see the points in a pdf output when pch="." and cex=0.5,  
but when directed to a jpg file, the points are no longer visible on  
my Mac 10.5.6 running R 2.8.1 Patched (2009-01-07 r47515)

-- 
David Winsemius

On Jan 21, 2009, at 8:48 PM, davidfarr wrote:
>
> I am using the following script to make .jpg files.
>
> jpeg('plotx.jpg')
>
> ddat <-read.table("file",header=T)
> attach(ddat)
> tdat<-read.table("file1")
> plot 
> (xx1 
>
,yy1,type='p',pch=1,col="blue",cex=0.2,xlim=c(0,3.5),ylim=c(-75,75))
> points(tdat,col="green",pch=1,cex=0.2)
>
> dev.off()
>
> The problem is that I want the points to be very small; however, if  
> I make
> cex any smaller than 0.2 the plot in the .jpg file is blank. If I  
> run the
> commands from the console (on a Mac) - with the exception of jpeg()  
> and
> dev.off() then it works even if cex < 0.2. I've tried making .ps  
> files and
> converting to .jpg but then I run into different problems with the  
> animation
> software (imageJ).
>
> Thanks for any suggestions
> -- 
> View this message in context:
http://www.nabble.com/Problem-with-cex%3D0.1-when-making-jpegs-tp21593744p21593744.html
> Sent from the R help mailing list archive at Nabble.com.
>
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