Message-ID: <CANVKczOCThmBqhZTAsxWYAPa0fgua3Esa2nAh0P+rvSeXJ=83Q@mail.gmail.com>
Date: 2013-11-26T10:12:51Z
From: Barry Rowlingson
Subject: specify breaks in divergent palette in RColorBrewer: was divergent colors around zero in levelplot()
In-Reply-To: <c1e075cf5f724ea387e7ba261b331863@EX-1-HT0.lancs.local>
On Tue, Nov 26, 2013 at 9:58 AM, Prof Brian Ripley
<ripley at stats.ox.ac.uk> wrote:
>> But the image function (and probably levelplot) doesn't allow that so
>
> Mis-information alert! The help says
>
> col: a list of colors such as that generated by ?rainbow?,
> ?heat.colors?, ?topo.colors?, ?terrain.colors? or similar
> functions.
>
> and look at what they generate. Or see e.g. ?col2rgb .
>
> Although base graphics has the concept of a palette of colours, AFAIK it
> has always been bolted on top of a general colour specification,
> originally RGB and for many years already RGBA.
Yes image allows you to specify col=, but it always specifies a
palette. The matrix values are scaled from 1:length(col) and looked up
in that palette. You can't call image with z as matrix of colours and
get those colours, nor set col to a matrix of colours and a see those
colours laid out. This is unlike points() where specifying col= as a
vector of the same length as the number of points gives you a 1:1
mapping of points to colours.
To do image() with a 1:1 mapping of cell values to colours requires a
tiny bit of hoop-jumping.
Barry