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
240 def grayscale_entry(bit_depth)
241   value = ChunkyPNG::Canvas.send(:"decode_png_resample_#{bit_depth}bit_value", content.unpack('n')[0])
242   ChunkyPNG::Color.grayscale(value)
243 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
216 def palette_alpha_channel
217   content.unpack('C*')
218 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
226 def truecolor_entry(bit_depth)
227   values = content.unpack('nnn').map do |c|
228     ChunkyPNG::Canvas.send(:"decode_png_resample_#{bit_depth}bit_value", c)
229   end
230   ChunkyPNG::Color.rgb(*values)
231 end