#Load 
library(imager)
#> Warning: package 'imager' was built under R version 3.5.3
#> Loading required package: magrittr
#> 
#> Attaching package: 'imager'
#> The following object is masked from 'package:magrittr':
#> 
#>     add
#> The following objects are masked from 'package:stats':
#> 
#>     convolve, spectrum
#> The following object is masked from 'package:graphics':
#> 
#>     frame
#> The following object is masked from 'package:base':
#> 
#>     save.image


#load images
im <- load.image('./22.jpg')
plot(im)

#filter by channels
im0 <- grayscale(im)
im1 <- channel(im,1) #red
im2 <- channel(im,2) #green
im3 <- channel(im,3) #blue


###ROI extraction
library(colocr)

img_rois <- im %>%
  roi_select(threshold = 50, n = 7)
# class of the returned object
class(im); class(img_rois)
#> [1] "cimg"         "imager_array" "numeric"
#> [1] "cimg"         "imager_array" "numeric"

# name of added attribut
names(attributes(im)); names(attributes(img_rois))
#> [1] "class" "dim"
#> [1] "class" "dim"   "label"

# str of labels
label <- attr(img_rois, 'label')
str(label)
#>  num [1:197690] 0 0 0 0 0 0 0 0 0 0 ...

# unique labels 
unique(label)
#> [1] 0 1 2 3 4 5 6 7
# select ROI and show the results
par(mfrow = c(2,2), mar = rep(1, 4))

img_rois %>%
  roi_show()