[R] bmp() shifts the image (Windows XP)

[William Simpson]

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 <murdoch.duncan at gmail.com> 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
>>
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