emani

Is it wise to convert 16 into 8 bit as it would increase ur processing speed.....does any one know some advantages regarding the conversion? Any research paper would also be helpful in this topic

Hi, Thanks for the reply....I actually stretched the image in R using this code which was given to me by my friend and now I see that my DN values have changed as I checked them on ERDAS. As digital number should be an Integer but all the values I got after running this code were fractions. I am posting the code which I used below. rm(list=ls(all=TRUE)) require(rgdal) require(rgl) require(maptools) StartPath <- getwd() #Defining the root directory Root <- "E:/Programming/Emani" Path_in <- paste(Root, "/Input",sep="") Path_out <- paste(Root, "/Output",sep="") dir.create(Path_out,showWarnings=FALSE, recursive=TRUE) hist.strecth <- function(x) { n <- dim(x)[2] for(k in 1:n) { data <- x[,k] cur.lim <- quantile(data,c(0.025,0.975),na.rm=TRUE) data <- pmax(cur.lim[1],pmin(cur.lim[2],data)) data <- floor(255*(data-cur.lim[1])/(cur.lim[2]-cur.lim[1])) data[is.na(data)]<-0 x[,k] <- data } return(x) } #====================================================================================== # Read image #====================================================================================== image.fn <- "LAUW_20130327" A <- readGDAL(paste(Path_in,"/",image.fn,".tif",sep="")) Nb <- dim(A@data)[2] #summary(A@data) # Read vector file, for subsetting vector.fn <- "extent" V <- readOGR(paste(Path_in,"/",vector.fn, sep=""), layer=vector.fn) i<-1 j<-1 polxy <- coordinates(V@polygons[[i]]@Polygons[[j]]) xy <- coordinates(A) tmp <- point.in.polygon(xy[,1],xy[,2],polxy[,1],polxy[,2]) ind <- which(tmp==1) indout<- which(tmp!=1) minDN <- array(0,Nb) maxDN <- array(0,Nb) for(k in 1:Nb) { x <- A@data[ind,] minDN[k] <- min(x[,k]) data <- x[,k] maxDN[k] <- quantile(data,0.99,na.rm=TRUE) } Acalibrated <- A for(k in 1:Nb) { x <- A@data[ind,k] x <- x-minDN[k] x <- x*255/(maxDN[k]-minDN[k]) x[x<0] <- 0 x[x>255]<-255 Acalibrated@data[ind,k] <- x } Acalibrated@data[indout,] <- 0 hist(Acalibrated@data$band4) # output MRF solution to a .tif file OUT <- Acalibrated setwd(Path_out) imagefn.out <- paste(image.fn,"_calibrated.tif",sep="") OUT.tif<-create2GDAL(OUT,drivername="GTiff",type="Float32",mvFlag=-1) saveDataset(OUT.tif,imagefn.out) GDAL.close(OUT.tif) setwd(StartPath) # The End thanks emani

Does the value of digital number change after linear stretching? And is it fine to obtain vegetation indices from linerly stretched images? Thanks Emani