Dear Marta, I did it in Matlab, and fiddled around with R code until I had *almost* the same result. The "almost" is probably due to R handling the picture values (ranging from 0 to 1) differently than Matlab (ranging from 0 to 255), and simply multiplying the R picture values by 255 did NOT result in exactly the same values as the Matlab values. [what seems white in the picture is 245 in Matlab, although values potentially range to 255, and white is 0.9642549 in R, which multiplied by 255 gives 245.12, e.g.] But maybe the precision of this solution is good enough for you ..
The corr2 demand from matlab is a 2D correlation coefficient - the R command cor works elementwise, and is not the solution here. Below I tried to implement the formula given in the following matlab page: http://www.mathworks.com/access/helpdesk/help/toolbox/images/corr2.html Maybe somebody on the list has a nice idea how to make the code more elegant This is the complete code in R setwd("D:/ wherever ") library(ReadImages) x <- read.jpeg(" whichever .jpg") #open image plot(x) #plot image x <- rgb2grey(x) #convert to greyscale plot(x) # check ;-) the image is in grey scale ImageWidth = dim(x)[2] #number of col MaxOffset = 99; #defined variable ImageWidthToProcess = ImageWidth-MaxOffset; #col-defined variable ## this one does NOT work because matrices not square: for(k in 1: MaxOffset) { OffsetPlaquette <- x[ , c((1+ k) : (ImageWidthToProcess + k))] dataToProcess <- x[,c(1:ImageWidthToProcess)] AutoCData[k] <- mantel(OffsetPlaquette, dataToProcess) } AutoCData ## END this one does not work because matrices not square AutoCData <- rep(0, MaxOffset) sumBothM <- rep(0, MaxOffset) sum1stMsq <- rep(0, MaxOffset) sum2ndMsq <- rep(0, MaxOffset) for(k in 1: MaxOffset) { OffsetPlaquette <- x[ ,(1+k) : (ImageWidthToProcess + k)] dataToProcess <- x[,c(1:ImageWidthToProcess)] meanM <- mean(OffsetPlaquette); meanM2 <- mean(dataToProcess) for(j in 1:dim(dataToProcess)[2]){ for(i in 1:dim(OffsetPlaquette)[1]){ sumBothM[k] <- sumBothM[k] + (OffsetPlaquette[i,j]-meanM)*(dataToProcess[i,j]-meanM2) sum1stMsq[k] <- sum1stMsq[k] + (OffsetPlaquette[i,j]-meanM)2 sum2ndMsq[k] <- sum2ndMsq[k] + (dataToProcess[i,j]-meanM2)2 } } AutoCData[k] <- sumBothM[k]/(sqrt(sum1stMsq[k] * sum2ndMsq[k])) } AutoCData Best wishes, Susanne __________________________________________________ Do You Yahoo!? Sie sind Spam leid? Yahoo! Mail verfügt über einen herausragenden Schutz gegen Massenmails. http://mail.yahoo.com ______________________________________________ R-help@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.
