Sorry, I meanwhile realized -- specifying rgb(255, 128, 128, alpha=0.5*255, maxColorValue=255)
and rgb(1.0, 0.5, 0.5, alpha=0.5, maxColorValue=1) gives you (virtually) identical results, i.e., you need to also specify the "alpha" parameter in the range given by the "maxColorValue" argument. Sorry for the confusion, Christian On Fri, 2019-07-26 at 10:27 +0200, Christian Röver wrote: > Hi, > > I experienced a problem with the "rgb()" function. > These two calls should (and do) return identical results: > > rgb(255, 128, 128, maxColorValue=255) > rgb(1.0, 0.5, 0.5, maxColorValue=1) > > However, when I specify a non-default "alpha" channel (a > "transparent" > colour), I get differing results: > > rgb(255, 128, 128, alpha=0.5, maxColorValue=255) > rgb(1.0, 0.5, 0.5, alpha=0.5, maxColorValue=1) > > where only the latter version seems to yield the actually intended > result. > > Is this a bug? > > > You can check the actual colours' appearance this way: > > barplot(3:5, col=rgb(255, 128, 128, maxColorValue=255)) > barplot(3:5, col=rgb(1.0, 0.5, 0.5, maxColorValue=1)) > > barplot(3:5, col=rgb(255, 128, 128, alpha=0.5, maxColorValue=255)) > barplot(3:5, col=rgb(1.0, 0.5, 0.5, alpha=0.5, maxColorValue=1)) > > The apparently buggy version in this case seems to return white > instead > of red. > > > Thanks, > > Christian ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
