R help - Jan 2010 - PNG resolution

Hi,

I expect that if I change only the resolution of an image, although the 
image would have more pixels, if viewed in the same physical size, the 
elements in the image would have the same physical size but with more 
detail.  However, when I use the "res" parameter of png() this is not 
what I see.  Would someone show me how I can just "increase the 
resolution" without changing the physical sizes of elements in my plot?

Maybe an example would help?  Below are three images.  I expect that if 
I print them out, let's say scaled to fit the page, then items such as 
the words "Title Text" would appear the same size.  Instead (for the 
last two) it appears that the same number of pixels are being used, thus 
the text size appears smaller.

What should I do to just increase the resolution?

png("72dpi.png", width=6+2/3, height=6+2/3, units="in",
res=72)
plot(0,0, main="Title Text")
dev.off()

png("300dpi.png", width=6+2/3, height=6+2/3, units="in",
res=300)
plot(0,0, main="Title Text")
dev.off()

png("600dpi.png", width=6+2/3, height=6+2/3, units="in",
res=600)
plot(0,0, main="Title Text")
dev.off()

Thanks in advance,

Matthew Walker

Matthew Walker wrote:
> 
> I expect that if I change only the resolution of an image, although the 
> image would have more pixels, if viewed in the same physical size, the 
> elements in the image would have the same physical size but with more 
> detail. 
> 
> 
The sample you provided create figures with the same relative size of text
and title on Windows and R 2.10.1. I remember, however, that I had similar
problem before, so possibly it has been fixed and you are using an older
version or a different operating system.

Also have a look at the Cairo devices; I have used them with good success in
similar cases.

Dieter


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Hello Matthew,

I do not have a direct answer to your problem, but you could try saving it
as an EPS and then rasterizing it using a graphics program (e.g., GIMP) to
whatever resolution you wanted.

Best luck finding a real solution.


Joshua



On Tue, Jan 26, 2010 at 9:05 AM, Matthew Walker
<matthew.walker.1@ulaval.ca>wrote:
> Hi,
>
> I expect that if I change only the resolution of an image, although the
> image would have more pixels, if viewed in the same physical size, the
> elements in the image would have the same physical size but with more
> detail.  However, when I use the "res" parameter of png() this is
not what I
> see.  Would someone show me how I can just "increase the
resolution" without
> changing the physical sizes of elements in my plot?
>
> Maybe an example would help?  Below are three images.  I expect that if I
> print them out, let's say scaled to fit the page, then items such as
the
> words "Title Text" would appear the same size.  Instead (for the
last two)
> it appears that the same number of pixels are being used, thus the text
size
> appears smaller.
>
> What should I do to just increase the resolution?
>
> png("72dpi.png", width=6+2/3, height=6+2/3, units="in",
res=72)
> plot(0,0, main="Title Text")
> dev.off()
>
> png("300dpi.png", width=6+2/3, height=6+2/3,
units="in", res=300)
> plot(0,0, main="Title Text")
> dev.off()
>
> png("600dpi.png", width=6+2/3, height=6+2/3,
units="in", res=600)
> plot(0,0, main="Title Text")
> dev.off()
>
> Thanks in advance,
>
> Matthew Walker
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
>
http://www.R-project.org/posting-guide.html<http://www.r-project.org/posting-guide.html>
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Joshua Wiley
Senior in Psychology
University of California, Riverside
http://www.joshuawiley.com/

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