You could apply a contrast enhancement using the stretch argument:

library(raster)

slogo <- stack(system.file("external/rlogo.grd", package="raster"))
slogo <- slogo - 100
slogo

plotRGB(slogo, stretch = 'lin')



On Fri, Aug 9, 2013 at 9:02 AM, amluiz <amommendes@hotmail.com> wrote:

>
>
> Thanks Etienne
> I was trying to plot three PCA axes (each one representing R, G and B
> color bands) in the map, but without success in R. I only can do this in
> GIS software...
> Any suggestion?
>
> Date: Tue, 6 Aug 2013 13:51:55 -0700
> From: ml-node+s2731867n7584357h83@n2.nabble.com
> To: amommendes@hotmail.com
> Subject: Re: plotRGB - negative values
>
>
>
>         Amom, you could probably offset your values and make sure you set
> scale to
>
> the right value. If your lowest value is 1 and the highest value then
>
> becomes 2, then something like
>
> plotRGB(all.pca + 1, scale = 2)
>
>
> I don't think you can use negative values in plotRGB.
>
>
> Etienne
>
>
>
> 2013/8/6 amluiz <[hidden email]>
>
>
> > Hello,
>
> >
>
> > I'm trying to use plotRGB. But I've negative values in my rasters cells
> and
>
> > I get the following error:
>
> >
>
> > plotRGB(all.pca)
>
> > Error in rgb(RGB[, 1], RGB[, 2], RGB[, 3], alpha = alpha, max = scale) :
>
> >   color intensity -1, not in 0:255
>
> >
>
> > Is there some way to solve this?
>
> >
>
> > Thanks in advance,
>
> >
>
> > Amom
>
> >
>
> >
>
> >
>
> >
>
> >
>
> > --
>
> > View this message in context:
>
> >
> http://r-sig-geo.2731867.n2.nabble.com/plotRGB-negative-values-tp7584356.html
> > Sent from the R-sig-geo mailing list archive at Nabble.com.
>
> >
>
> > _______________________________________________
>
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-- 
*Andrew P. Vitale*
Masters Student
Department of Geography
University of Nevada, Reno
(412) 915-3632
vitale232@gmail.com

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