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(

[email protected])[2]
#summary(

[email protected])
# 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(

[email protected][[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 <-

[email protected][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 <-

[email protected][ind,k]
x <- x-minDN[k]
x <- x*255/(maxDN[k]-minDN[k])
x[x<0] <- 0
x[x>255]<-255

[email protected][ind,k] <- x
}

[email protected][indout,] <- 0
hist(

[email protected]$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