[R] count pixels of same color in pixmap object?
Roger.Bivand at nhh.no
Thu Mar 9 18:47:57 CET 2006
On Thu, 9 Mar 2006, Christian Jost wrote:
> Dear all,
> I try to figure out how to use R to count the number of pixels of the
> same color in some gray-level picture. I managed to read it in either
> tiff or jpeg format, but the returned pixmap object keeps its
> information out of (my) reach. Is there an easy way to tabulate the
> different color/graylevel pixels and their numbers? Or should I use a
> completely different (free) software?
The objects are new-style class objects, so they are documented internally
- query by getSlots() or from ?"pixmap-class":
x <- read.pnm(system.file("pictures/logo.ppm", package="pixmap"))
z <- as(x, "pixmapGrey")
getSlots(class(z)) # lets you know what the slots are
greydata <- slot(z, "grey") # extract the slot object
summary(c(greydata)) # c() to flatten a matrix
length((c(greydata))) # rather a lot of different values, let's round:
rgreydata <- round(greydata*10)
length(unique(c(rgreydata))) # looks good
I assume that you converted from tiff or jpeg to pnm outside pixmap.
> Thanks for any hint, Christian.
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
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e-mail: Roger.Bivand at nhh.no
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