R help - Mar 2013 - Raster images and saving with original pixel dimensions in tiff, jpeg, or png perferablly.

Hello R-Help,

I want to be able to read in a raster image, plot it with grid.raster
or rasterImage and save the image with one pixel per a pixel element
from my array. Saved preferably in a common image format.

The real goal of my question is to eventually read in images with text
on them, manipulate them with my controlled functions, save them
without changing the image dimensions, and perform OCR outside R.

I have read The R Journal article on raster images
(http://journal.r-project.org/archive/2011-1/RJournal_2011-1_Murrell.pdf)
and have experimented with some of the par() variables with no
success.  There are some arguments in gird.raster that elude me
currently on how to use them.  These include, vjust, hjust,
default.units, gp and vp.  Perhaps these are what I need to use but I
am getting nowhere without more documentation.

Here is the basic code I've used to experiment with making this work.
The end result I'm hoping for would be an image exactly like the one
I've read in (Rlogo.jpg for this small example).  I turned off
dev.copy lines because I'm not sure on the guidelines for file writing
functions.

Thanks,
Hans Thompson

Forgive me If I made any mistakes following posting guidelines.

####START#####
library(jpeg)
library(grid)

img <- readJPEG(system.file("img", "Rlogo.jpg",
package="jpeg"))
grid.raster(img, interpolate =F)
#turnon next line for output. Don't want to accidentally write any
unwanted files.
#dev.copy(tiff, "outputimage.tiff")
dev.off()

#or using package = "graphics" but not perfered.

library(graphics)

plot( c(0, dim(img)[2]), c(0, dim(img)[1]), type = "n", xlab =
"", ylab = "")
rasterImage(img, 0, 0, dim(img)[2], dim(img)[1])
#dev.copy(tiff, "outputfile2.tiff")
dev.off()

##STOP##

Hi

It sounds like you just want to control the size of the external raster 
image that you are creating.  For example ...

library(grid)

im <- matrix(0:1, ncol=3, nrow=3)

# grid.newpage()
grid.raster(im, interpolate=FALSE)

png("ident.png", 3, 3)
grid.raster(im, interpolate=FALSE)
dev.off()

Does that help?

Paul

On 03/03/13 11:03, Hans Thompson wrote:
> Hello R-Help,
>
> I want to be able to read in a raster image, plot it with grid.raster
> or rasterImage and save the image with one pixel per a pixel element
> from my array. Saved preferably in a common image format.
>
> The real goal of my question is to eventually read in images with text
> on them, manipulate them with my controlled functions, save them
> without changing the image dimensions, and perform OCR outside R.
>
> I have read The R Journal article on raster images
> (http://journal.r-project.org/archive/2011-1/RJournal_2011-1_Murrell.pdf)
> and have experimented with some of the par() variables with no
> success.  There are some arguments in gird.raster that elude me
> currently on how to use them.  These include, vjust, hjust,
> default.units, gp and vp.  Perhaps these are what I need to use but I
> am getting nowhere without more documentation.
>
> Here is the basic code I've used to experiment with making this work.
> The end result I'm hoping for would be an image exactly like the one
> I've read in (Rlogo.jpg for this small example).  I turned off
> dev.copy lines because I'm not sure on the guidelines for file writing
> functions.
>
> Thanks,
> Hans Thompson
>
> Forgive me If I made any mistakes following posting guidelines.
>
> ####START#####
> library(jpeg)
> library(grid)
>
> img <- readJPEG(system.file("img", "Rlogo.jpg",
package="jpeg"))
> grid.raster(img, interpolate =F)
> #turnon next line for output. Don't want to accidentally write any
> unwanted files.
> #dev.copy(tiff, "outputimage.tiff")
> dev.off()
>
> #or using package = "graphics" but not perfered.
>
> library(graphics)
>
> plot( c(0, dim(img)[2]), c(0, dim(img)[1]), type = "n", xlab =
"", ylab = "")
> rasterImage(img, 0, 0, dim(img)[2], dim(img)[1])
> #dev.copy(tiff, "outputfile2.tiff")
> dev.off()
>
> ##STOP##
>
> ______________________________________________
> R-help at r-project.org 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.
>
-- 
Dr Paul Murrell
Department of Statistics
The University of Auckland
Private Bag 92019
Auckland
New Zealand
64 9 3737599 x85392
paul at stat.auckland.ac.nz
http://www.stat.auckland.ac.nz/~paul/