Hello, I've a problem aligning tickmarks to an image. I've created a correlation matrix for 84 affy mouse chips. I'm visualizing the matrix as an image with colour coding according to the correlation coefficient. The 84 chips are distributed over three factors, but the desgin is unbalanced, so that the tickarks and the lables for the axis are must not evenly distributed. A regular grid via the 'grid' function aligns perfectly with the image cells, but the tickmarks seem to be shifted, and not aligned perfectly with the image cells. This offset is even stonger for the y-axis. The thing is that I don't want 84 lables at the axis, it's enough to have one lable for all the different factor level combinations, which results in 28 labels. Maybe you have an idea how to setup the command to align the tick marks. kind regards, Arne Here are my commands: > library(marrayPlots) # for the colors > col <- maPalette(low='white', high='darkred', k=50) > par(ps=8, cex=1, mar=c(1,5,5,1)) # space needed for lables @ axis 1 and 3 # a x and y tange from 1 to 84, x is the correlation matrix (dim = 84x84) > image(1:84, 1:84, x, col=col, xaxt='n', yaxt='n', xlab='', ylab='') # set up the axis > axis(3, i, labels=names(l), las=2, tick=T) > axis(2, i, labels=names(l), las=2, tick=T) > grid(84, col='black', lty='solid') # this is where i get the lables from > l NEW:4:0 NEW:4:100 NEW:4:250 NEW:4:500 NEW:4:1000 NEW:24:0 3 3 3 3 3 3 NEW:24:100 NEW:24:250 NEW:24:500 NEW:24:1000 OLD:4:0 OLD:4:100 3 3 3 3 4 3 OLD:4:250 OLD:4:500 OLD:4:1000 OLD:24:0 OLD:24:100 OLD:24:250 2 3 3 4 3 2 OLD:24:500 OLD:24:1000 PRG:4:0 PRG:4:100 PRG:4:250 PRG:4:1000 3 3 3 3 3 3 PRG:24:0 PRG:24:100 PRG:24:250 PRG:24:1000 3 3 3 3 # these are the positions along the axis for the tick marks, technical # replicates from 1 to 3 (replicates of one factor level combination), 4 to 6 # ... > i [1] 3 6 9 12 15 18 21 24 27 30 34 37 39 42 45 49 52 54 57 60 63 66 69 72 75 [26] 78 81 84