>>>>> "Scott" == Scott Harrison <[EMAIL PROTECTED]>
>>>>> on Thu, 14 Oct 2004 11:13:16 -0400 writes:
Scott> Hi: Goal: use R to turn a matrix of 1's and 0's into
Scott> a corresponding image (e.g. png) of black and white
Scott> pixels.
Scott> Why R: Yes, I can do this more efficiently and
Scott> precisely with a perl module like Image::PBM. Been
Scott> there, done that many times, etc. (Just humor me.
Scott> I'm trying to do this with R for a number of
Scott> reasons.)
Scott> Problem: Difficult to get a perfect rasterization.
Scott> There can be appended or removed pixel columns or
Scott> pixel rows depending on plot region dimensions. I
Scott> witness this with both R version 1.8.1 and R version
Scott> 2.0.
<....>
Scott> There are alternatives to rect (plot with type="p",
Scott> pch=".", etc) and I have also tried png() instead of
Scott> bitmap(). (I do prefer bitmap so this can run
Scott> without x11.)
I think the "most typical" alternative is to use image()
which is probably the most efficient currently --- it is used by
the plot() method of "pixmap" objects in package 'pixmap' {which
you probably should really look at!}.
Note however that image() is still very inefficient for
high-resolution (already 1000x1000) images since it really fills
a rectangular polygon for each pixel. This e.g. leads to
horribly large postscript files when plotting such pixmaps.
In some way, this is a known "missing feature" in R's graphics
engines. However a nice implementation would probably use
properties of the graphics device:
A smartImage() function would ``see'' that for a given output
device, it should only draw pixels instead of rects(); even
smarter for even larger pixmaps (where there are less "pixels"
on the output device than you have in your image) it would even average
("color-smooth") neighboring pixmap pixels into device pixels.
Scott> I am guessing that R's internal region calculations
Scott> are vector based, which generally makes sense for
Scott> most statistical plots. However, I do have some
Scott> ideas for R and the presentation of cellular automata
Scott> results.
Scott> Any tips out there? (Is it just a matter of
Scott> height=50px to overcome the inches default,
Scott> etc?).....
Scott> Regards, Scott
Regards,
Martin Maechler
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