Split images losing color when saving RasterBrick array as *jpg - jpeg

Question

#Packages
library(raster)
library(rgeos)
library(rgdal)
library(jpeg)
I have a RGB color *jpg image:
## Open my RGB image
path<-"https://raw.githubusercontent.com/Leprechault/trash/main/IMG_191022_134242_0000_RGB.JPG" # Image path
download.file(path, "IMG_191022_134242_0000_RGB.JPG", mode = "wb")
rc<-stack(raster("IMG_191022_134242_0000_RGB.JPG")) #Open as a raster and stack
plot(rc)
When I try to split in 16 images of equal size:
# This function spatially aggregates the original raster
# it turns each aggregated cell into a polygon
# then the extent of each polygon is used to crop
# the original raster.
# The function returns a list with all the pieces
# it saves and plots each piece
# The arguments are:
# raster = raster to be chopped (raster object)
# ppside = pieces per side (integer)
# save = write raster (TRUE or FALSE)
# plot = do you want to plot the output? (TRUE or FALSE)
SplitRas <- function(raster,ppside,save,plot){
h <- ceiling(ncol(raster)/ppside)
v <- ceiling(nrow(raster)/ppside)
agg <- aggregate(raster,fact=c(h,v))
agg[] <- 1:ncell(agg)
agg_poly <- rasterToPolygons(agg)
names(agg_poly) <- "polis"
r_list <- list()
for(i in 1:ncell(agg)){
e1 <- extent(agg_poly[agg_poly$polis==i,])
r_list[[i]] <- crop(raster,e1)
}
if(save==T){
for(i in 1:length(r_list)){
options(max.print=999999)
#EBImage::writeImage(as.array(r_list[[i]]/255), paste0("sample_",i,".jpg",sep=""),quality = 100)
writeJPEG(as.array(r_list[[i]]/255), target = paste0("sample_",i,".jpg",sep=""),quality = 1,color.space="RGBA")
}
}
return(r_list)
}
#Slip RGB raster in 16 subimages
splitRBG<-SplitRas(raster=rc,ppside=4,save=TRUE)
#
The results are greyscaled images, eg. 1 (sample_1.jpg) of the 16 images:
I try to make a lot of changes in writeJPEG() function (something is wrong in the as.array(r_list[[i]]/255)code or in the color.space) without success, please any ideas?

Answer 1

Solution: split each RGB channel in a individual raster layer (rst.blue,rst.green nad rst.red) and stack before the crop operation with SplitRas custom function and works!!
#Packages
library(raster)
library(rgeos)
library(rgdal)
library(jpeg)
## download RGB image
path<-"https://raw.githubusercontent.com/Leprechault/trash/main/IMG_191022_134242_0000_RGB.JPG" # Image path
download.file(path, "IMG_191022_134242_0000_RGB.JPG", mode = "wb")
# Open jpeg file
jpg<-readJPEG("IMG_191022_134242_0000_RGB.JPG")
# Convert imagedata to raster
rst.blue <- raster(jpg[,,1])
rst.green <- raster(jpg[,,2])
rst.red <- raster(jpg[,,3])
rc<-stack(rst.blue, rst.green, rst.red)
# This function spatially aggregates the original raster
# it turns each aggregated cell into a polygon
# then the extent of each polygon is used to crop
# the original raster.
# The function returns a list with all the pieces
# it saves and plots each piece
# The arguments are:
# raster = raster to be chopped (raster object)
# ppside = pieces per side (integer)
# save = write raster (TRUE or FALSE)
# plot = do you want to plot the output? (TRUE or FALSE)
SplitRas <- function(raster,ppside,save,plot){
h <- ceiling(ncol(raster)/ppside)
v <- ceiling(nrow(raster)/ppside)
agg <- aggregate(raster,fact=c(h,v))
agg[] <- 1:ncell(agg)
agg_poly <- rasterToPolygons(agg)
names(agg_poly) <- "polis"
r_list <- list()
for(i in 1:ncell(agg)){
e1 <- extent(agg_poly[agg_poly$polis==i,])
r_list[[i]] <- crop(raster,e1)
}
if(save==T){
for(i in 1:length(r_list)){
writeJPEG(as.array(r_list[[i]]), target = paste0("sample_",i,".jpg",sep=""),quality = 1)
}
}
return(r_list)
}
#Slip RGB raster in 4 equal parts
splitRBG<-SplitRas(raster=rc,ppside=4,save=TRUE)
#