I've written a piece of code (see below) to do a wavelet image
decomposition, during the evaluation of this code I would like to write
the results of some calculations back to the R root directory. I used
assign() to do so because the names should vary when going thrue a
while() loop. For some unknown reason I get an error that says:
Error in assign(varname[i], imwrImage) :
invalid first argument
what could be wrong, when I do it on the commandline everything works
out just fine. But within the function it doesn't. When I disable the
assign statement, everything runs fine so the rest of the code should be
clean.
My code:
# Wavelet multiresolution decomposition
wmra <- function(image_file){
#require(rimage)
require(wavethresh)
#reading image file and converting it to grayscale
#dimage <- read.jpeg(image_file)
#dimage <- imagematrix(dimage)
# discrete wavelet decomposition
imwdImage <- imwd(image_file)
# get a value for the number of decomposition levels
#nlevels <- imwdImage$nlevels
i <- 0
varname <- paste("level",0:(imwdImage$nlevels-1),sep="")
print(varname)
while ( i < imwdImage$nlevels)
{
# set the threshold to 0 on all levels except the one in evaluation
# thresholdLevels is the list of levels to set to zero
thresholdLevels <- 1:(imwdImage$nlevels-1)
thresholdLevels[i] <- 0
thresholdedCoeff <- threshold.imwd(imwdImage,levels=thresholdLevels,
policy=c("manual"), type="hard", value=10000)
# calculate the inverse wavelet transform
imwrImage <- imwr(thresholdedCoeff)
# assign the various decomposition level data a name
# starting at i+1 because i = 0.
assign(varname[i+1],imwrImage) # --> gives an error
# export the multiresolution decomposition for level i as graph
jpeg(paste("level",i,".jpg",sep=""),quality=100)
image(imwrImage,xlab=c("MRA image of level: ",i),col=gray(255:0/256))
dev.off()
i <- i + 1
}
}
Best regards, Koen
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