    # 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.




	[[alternative HTML version deleted]]


