Sierra 2-4a dithering

# Sierra 2-4a dithering filter

Sierra24aConvolution <- function(a){

c <- matrix(0, nrow=dim(a)[1], ncol=dim(a)[2])

for(i in 2:(dim(a)[1]-2)){
for(j in 2:(dim(a)[2]-2)){
	P <- trunc(a[i,j]+0.5)
	e <- a[i,j] - P
	a[i,j] <- P
	a[i,j+1] <- a[i,j+1] + (e * 2/4)
	a[i+1,j-1] <- a[i+1,j-1] + (e * 1/4)
	a[i+1,j] <- a[i+1,j] + (e * 1/4)
}
}
a
}


grey2S24adith <- function(img){
	greyMatrix <- img[1:nrow(img),1:ncol(img)]
dim1 <- 2 
dim2 <- 2
dim1x <- 2
dim2x <- 2
dim1a <- dim(greyMatrix)[1]
dim2a <- dim(greyMatrix)[2]

tempMatrix <- matrix(0.5, nrow=nrow(greyMatrix)+2*1, ncol=ncol(greyMatrix)+2*1)
tempMatrix[2:(nrow(tempMatrix)-1),2:(ncol(tempMatrix)-1)] <- greyMatrix

igrey <- Sierra24aConvolution(tempMatrix)

	imagematrix(igrey[2:(nrow(igrey)-1),2:(ncol(igrey)-1)], type="grey", noclipping=TRUE)
}