class HexaPDF::ImageLoader::PNG

def add_smask_image(dict, mask_data, from_indexed: false)

created from an indexed PNG and is not deflate encoded.
If the optional argument +from_indexed+ is +true+, it is assumed that the +mask_data+ was

data.
Adds a source mask image to the image described by +dict+ using +mask_data+ as the source 
def add_smask_image(dict, mask_data, from_indexed: false)
  decode_parms = {
    Predictor: 15,
    Colors: 1,
    BitsPerComponent: (from_indexed ? 8 : dict[:BitsPerComponent]),
    Columns: dict[:Width],
  }
  stream_opts = (from_indexed ? {} : {filter: :FlateDecode, decode_parms: decode_parms})
  stream = HexaPDF::StreamData.new(lambda { mask_data }, **stream_opts)
  smask_dict = {
    Type: :XObject,
    Subtype: :Image,
    Width: dict[:Width],
    Height: dict[:Height],
    ColorSpace: :DeviceGray,
    BitsPerComponent: (from_indexed ? 8 : dict[:BitsPerComponent]),
  }
  smask = @document.add(smask_dict, stream: stream)
  smask.set_filter(:FlateDecode, decode_parms)
  dict[:SMask] = smask
end