[Rd] Strange behaviour of image (PR#510)
Fri, 7 Apr 2000 17:04:17 +0100 (BST)
On 6 Apr 2000, Peter Dalgaard BSA wrote:
> J.C.Rougier@durham.ac.uk writes:
> > The following commands
> > z <- matrix(seq(0, 1, len=1000))
> > image(z, 1, z, zlim=c(0, 1), col=gray(1:10/10))
> > appear to violate the image functionality as described on the
> > help page. As I understand it, by specifying a zlim of c(0, 1)
> > and a colour vector of length 10, the colours should correspond
> > to the intervals (0, 0.1), (0.1, 0.2), ..., (0.9, 1.0), this
> > being 10 equally-spaced intervals on (0, 1). It is clear from
> > the image that this has not occurred. In fact the intervals are
> > apparently (0, 1/18), (1/18, 3/18), ..., (15/18, 17/18), (17/18,
> > 1). Have I misunderstood something?
> I don't see that anything else is being promised...
> If someone actually thought about this, then the choice might be
> related to the behavior at peaks and troughs. (since a circle with
> radius r looks wide compared to the region between two circles with
> diameter n*r and (n+1)*r)
I'm not quite sure I follow. My feeling is that the displayed behaviour
of image is unreasonable, and, I hazard, not what most people who use
image expect. I think the default behaviour of image should be to give
colour bands of equal widths, and, if I may append to the wish list, I
woud like to be able to specify a "breaks" argument to have unequal widths
should I so choose.
Jonathan Rougier Science Laboratories
Department of Mathematical Sciences South Road
University of Durham Durham DH1 3LE
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