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