def to_trns_chunk
      ChunkyPNG::Chunk::Transparency.new("tRNS", map { |c| ChunkyPNG::Color.a(c) }.pack("C*"))
    end
def to_trns_chunk
      ChunkyPNG::Chunk::Transparency.new("tRNS", map { |c| ChunkyPNG::Color.a(c) }.pack("C*"))
    end
Creates a tRNS chunk that corresponds with this palette to store the
 alpha channel of all colors.

 Note that this chunk can be left out of every color in the palette is
 opaque, and the image is encoded using indexed colors.

 @return [ChunkyPNG::Chunk::Transparency] The tRNS chunk.