# clear everything:
rm(list=ls(all=TRUE))
detach()
graphics.off()
# make a test matrix:
( m<- matrix((1:12)/12, 3, 4) )
library(gplots)
# display the test matrix:
image(m, col=colorpanel(12, "darkblue", "yellow", "white"), axes=FALSE)
# here's the action part (no index checking, lame, illustrative code only,
with advance apologies, &c.):
image.ij<- function(i,j) return( t(m)[dim(t(m))[1]:1,][i,j] )
# we're seeing a "1" in the top right-hand corner of the image at
coordinates:
i<- 1
j<- 3
image.ij(i,j)
# cf. what's in the matrix at those coordinates:
m[i,j]
> Hello.
>
>
> I have a matrix whit n1 rows and n2 columns called example.
> If I do image(example), R shows me an image with 480x480 pixels.
>
> How can I obtain the gray level of the pixel of row i and column j?
>
> Thanks,
>
> Arnau.
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