class ChunkyPNG::Chunk::Transparency
A transparency (tRNS) chunk defines the transparency for an image.
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For indexed images, it contains the alpha channel for the colors defined in the Palette (PLTE) chunk.
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For grayscale images, it contains the grayscale teint that should be considered fully transparent.
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For truecolor images, it contains the color that should be considered fully transparent.
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
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
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
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