Package check result: ERROR

Check: examples, Result: ERROR
  Running examples in ‘circlize-Ex.R’ failed
  The error most likely occurred in:
  
  > base::assign(".ptime", proc.time(), pos = "CheckExEnv")
  > ### Name: circos.raster
  > ### Title: Add raster images
  > ### Aliases: circos.raster
  > 
  > ### ** Examples
  > 
  > require(png)
  Loading required package: png
  Warning in library(package, lib.loc = lib.loc, character.only = TRUE, logical.return = TRUE,  :
    there is no package called ‘png’
  > image = system.file("extdata", "Rlogo.png", package = "circlize")
  > image = as.raster(readPNG(image))
  Error in readPNG(image) : could not find function "readPNG"
  Calls: as.raster
  Execution halted