Re: [Rd] pixmaps and R

From: Prof Brian Ripley <ripley_at_stats.ox.ac.uk>
Date: Mon 03 Apr 2006 - 10:28:58 GMT

On Mon, 3 Apr 2006, Thibaut Jombart wrote:

> Hello list,
>
> here is a question relative to pixmap pictures in R. Manipulating such
> objects is quite demanding for the RAM, as large matrices are created.
>
> For instance, try to execute the example of rimage library :
>
> ### R code ###
> library(rimage)
> x <- read.jpeg(system.file("data", "cat.jpg", package="rimage"))
> plot(x)
> object.size(x)
> save.image()
> ### end of R code ###
>
> Moreover, the '.RData' will be approximately the size of 'x' (around 4
> MB), despite the jpeg size is only 16 KB.

You can of course use compression when saving here, via save(compress=TRUE). But it will not help much, as you are storing a very simple image in a floating-point format with 24 bytes per pixel. I suggest you use a more suitable format: JPEG files are only 8bits per channel, so could be stored in a raw not numeric vector.

> Of course it is possible store only the expression reading the pictures
> instead.
> For instance:
>
> ### R code ###
> y=expression(read.jpeg(system.file("data", "cat.jpg", package="rimage")))
> object.size(y)
> object.size(eval(y))
> plot(eval(y))
> ### end of R code ###
>
> But... does anybody know if compressed pictures could be stored in R?
> And if yes, how ?
>
> Thanks,
>
> Thibaut.
>

-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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Received on Mon Apr 03 20:53:12 2006

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