Checking colour contrasts

ColourContrast.R

# Visual comparison of the contrast between colours and different solid backgrounds

colourGrid=function(dimval=20,background="gray",colourfun=rainbow,ptsize=1){
  cols=colourfun(dimval^2)
  yvals=rep(seq(0,1,length.out=dimval),each=dimval)
  xvals=rep(seq(0,1,length.out=dimval),dimval)
  plot(xvals,yvals,type="n",xaxt="n",yaxt="n",ann=FALSE, bty="n")
  rect(par("usr")[1],par("usr")[3],par("usr")[2],par("usr")[4],col = background,border=NA)
  points(xvals,yvals,col=cols,pch=16,cex=ptsize)
}

dimval=20
ptsize=1
op=par(mfrow=c(2,2),mai=c(0.1,0.1,0.1,0.1))
  colourGrid(dimval,"gray",rainbow,ptsize)
  colourGrid(dimval,"white",rainbow,ptsize)
  colourGrid(dimval,"gray",cm.colors,ptsize)
  colourGrid(dimval,"white",cm.colors,ptsize)
par(op)