The header (IHDR) chunk is the first chunk of every PNG image, and contains information about the image: i.e. its width, height, color depth, color mode, compression method, filtering method and interlace method.
ChunkyPNG supports all values for these variables that are defined in the PNG spec, except for color depth: Only 8-bit depth images are supported. Note that it is still possible to access the chunk for such an image, but ChunkyPNG will raise an exception if you try to access the pixel data.
# File lib/chunky_png/chunk.rb, line 119 def initialize(attrs = {}) super('IHDR', attrs) @depth ||= 8 @color ||= ChunkyPNG::COLOR_TRUECOLOR @compression ||= ChunkyPNG::COMPRESSION_DEFAULT @filtering ||= ChunkyPNG::FILTERING_DEFAULT @interlace ||= ChunkyPNG::INTERLACING_NONE end
Reads the 13 bytes of content from the header chunk to set the image attributes. @param [String] type The four character chunk type indicator (= "IHDR"). @param [String] content The 13 bytes of content read from the chunk. @return [ChunkyPNG::Chunk::End] The new Header chunk instance with the
variables set to the values according to the content.
# File lib/chunky_png/chunk.rb, line 133 def self.read(type, content) fields = content.unpack('NNC5') self.new(:width => fields[0], :height => fields[1], :depth => fields[2], :color => fields[3], :compression => fields[4], :filtering => fields[5], :interlace => fields[6]) end
Returns the content for this chunk when it gets written to a file, by packing the image information variables into the correct format. @return [String] The 13-byte content for the header chunk.
# File lib/chunky_png/chunk.rb, line 142 def content [width, height, depth, color, compression, filtering, interlace].pack('NNC5') end
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