I have figured out what I wanted to do using pixmap. Pixmap writes .pgm files which I will batch convert to .bmp using Irfanview.
Thanks for your help. Cheers, Bill On 1/2/12, William Simpson <[email protected]> wrote: > Duncan, I checked out as.raster as you suggested. However, I can't > find info on how to display and save a raster object. What a raster > object is eludes me. These were fruitless > ?as.raster > ?grDevices > library(help="grDevices") > ?windows > ?savePlot > > x<-as.raster(matrix(runif(n*n),nrow=n)) > > How to display x? plot(x) and image(x) don't work. > How to save the bitmap image x? > > Not sure if I need to scale x to be in range 0-255 before doing > as.raster(). > > I see that x contains elements like "#676767". > col2rgb("#676767") > [,1] > red 103 > green 103 > blue 103 > That doesn't help me display and save bitmap images. > > I see there is a package called raster but I'd rather avoid it, given > my very simple needs. Maybe package pixmap will work, then convert the > saved images to .bmp (e.g. using Irfanview in batch mode). > > Thanks very much for any help! > Bill > > > On 1/1/12, Duncan Murdoch <[email protected]> wrote: >> On 12-01-01 9:05 AM, William Simpson wrote: >>> When using bmp() under Windows XP, I find that the saved image is a >>> shifted version of the correct image. Try this: >> >> The image() function isn't designed to be able to do pixel-level >> addressing, so it's not too surprising that some rounding error >> somewhere leads to this. You could look through the Windows graphics >> device code to fix it. >> >> However, if you really need pixel level addressing, you should be using >> raster objects. I don't know if someone has written code to output a >> .bmp file, but it's a very simple format, so it shouldn't be too hard, >> especially if you only need a limited range of pixel formats (e.g. >> grayscale). >> >> Duncan Murdoch >> >>> >>> n<-5 >>> fn<-"01.bmp" >>> x<-matrix(runif(n*n),nrow=n) >>> image(x,col=gray(0:255/255),axes=F,frame.plot=F) >>> bmp(filename = fn,width = n, height = n, units = "px") >>> par(mar=c(0,0,0,0),pty="s") >>> image(x,col=gray(0:255/255),axes=F,frame.plot=F) >>> dev.off() >>> >>> The image 01.bmp is like this: >>> 22 23 24 25 w >>> 32 33 34 35 w >>> 42 43 44 45 w >>> 52 53 54 55 w >>> w w w w w w >>> Where 22 represents x[2,2], etc; w represents a white pixel. >>> >>> For my application, the image has to be .bmp format. The same shifting >>> behaviour is seen for large values of n. It is not just due to the >>> small n value. >>> >>> For my application, this shifting is important and has to be >>> eliminated. Please help. >>> >>> On an unrelated note, I found out that the bmp() code is "smart" >>> enough to write my image as 8-bit using a palette instead of 24-bit >>> with 0:255 grey levels if the image being saved does not use all 256 >>> grey levels. I would love to hear it if somebody knows a good way to >>> make bmp() stupid and always save as 24-bit. My kludge, using 256x256 >>> pixel images, is to tack on an extra row with grey levels 0:255. Then >>> when displaying, I have to crop the image to get rid of that bogus >>> row. >>> >>> Thanks very much for any help! >>> Bill >>> >>> ______________________________________________ >>> [email protected] mailing list >>> 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. >> >> > ______________________________________________ [email protected] mailing list 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.
