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Problem with cex=0.1 when making jpegs

2 messages · davidfarr, David Winsemius

#
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
#
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)