class ChunkyPNG::Chunk::Transparency

A transparency (tRNS) chunk defines the transparency for an image.

Images having a color mode that already includes an alpha channel, this chunk should not be included.

@see ChunkyPNG::Chunk::Palette @see ChunkyPNG::Palette

Public Instance Methods

grayscale_entry(bit_depth) click to toggle source

Returns the grayscale entry to be replaced by transparent pixels.

This method should only be used for images having color mode ChunkyPNG::COLOR_GRAYSCALE (0).

@return [Integer] The (grayscale) color to replace with fully transparent pixels.

# File lib/chunky_png/chunk.rb, line 216
def grayscale_entry(bit_depth)
  value = ChunkyPNG::Canvas.send(:"decode_png_resample_#{bit_depth}bit_value", content.unpack('n')[0])
  ChunkyPNG::Color.grayscale(value)
end
palette_alpha_channel() click to toggle source

Returns the alpha channel for the palette of an indexed image.

This method should only be used for images having color mode ChunkyPNG::COLOR_INDEXED (3).

@return [Array<Integer>] Returns an array of alpha channel values [0-255].

# File lib/chunky_png/chunk.rb, line 197
def palette_alpha_channel
  content.unpack('C*')
end
truecolor_entry(bit_depth) click to toggle source

Returns the truecolor entry to be replaced by transparent pixels,

This method should only be used for images having color mode ChunkyPNG::COLOR_TRUECOLOR (2).

@return [Integer] The color to replace with fully transparent pixels.

# File lib/chunky_png/chunk.rb, line 206
def truecolor_entry(bit_depth)
  values = content.unpack('nnn').map { |c| ChunkyPNG::Canvas.send(:"decode_png_resample_#{bit_depth}bit_value", c) }
  ChunkyPNG::Color.rgb(*values)
end