class ChunkyPNG::Chunk::Transparency
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 www.w3.org/TR/PNG/#11tRNS @see ChunkyPNG::Chunk::Palette
@see ChunkyPNG::Palette
Public Instance Methods
Source
# File lib/chunky_png/chunk.rb 254 def grayscale_entry(bit_depth) 255 value = ChunkyPNG::Canvas.send(:"decode_png_resample_#{bit_depth}bit_value", content.unpack("n")[0]) 256 ChunkyPNG::Color.grayscale(value) 257 end
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.
Source
# File lib/chunky_png/chunk.rb 231 def palette_alpha_channel 232 content.unpack("C*") 233 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].
Source
# File lib/chunky_png/chunk.rb 241 def truecolor_entry(bit_depth) 242 decode_method_name = :"decode_png_resample_#{bit_depth}bit_value" 243 values = content.unpack("nnn").map { |c| ChunkyPNG::Canvas.send(decode_method_name, c) } 244 ChunkyPNG::Color.rgb(*values) 245 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.