Class: ChunkyPNG::Chunk::Header

Inherits:
Base
  • Object
show all
Defined in:
lib/chunky_png/chunk.rb

Overview

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.

Instance Attribute Summary (collapse)

Attributes inherited from Base

#type

Class Method Summary (collapse)

Instance Method Summary (collapse)

Methods inherited from Base

#write, #write_with_crc

Constructor Details

- (Header) initialize(attrs = {})

A new instance of Header



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# 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

Instance Attribute Details

- (Object) color

Returns the value of attribute color



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# File 'lib/chunky_png/chunk.rb', line 117

def color
  @color
end

- (Object) compression

Returns the value of attribute compression



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# File 'lib/chunky_png/chunk.rb', line 117

def compression
  @compression
end

- (Object) depth

Returns the value of attribute depth



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# File 'lib/chunky_png/chunk.rb', line 117

def depth
  @depth
end

- (Object) filtering

Returns the value of attribute filtering



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# File 'lib/chunky_png/chunk.rb', line 117

def filtering
  @filtering
end

- (Object) height

Returns the value of attribute height



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# File 'lib/chunky_png/chunk.rb', line 117

def height
  @height
end

- (Object) interlace

Returns the value of attribute interlace



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# File 'lib/chunky_png/chunk.rb', line 117

def interlace
  @interlace
end

- (Object) width

Returns the value of attribute width



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# File 'lib/chunky_png/chunk.rb', line 117

def width
  @width
end

Class Method Details

+ (ChunkyPNG::Chunk::End) read(type, content)

Reads the 13 bytes of content from the header chunk to set the image attributes.

Parameters:

  • type (String) —

    The four character chunk type indicator (= “IHDR”).

  • content (String) —

    The 13 bytes of content read from the chunk.

Returns:

  • (ChunkyPNG::Chunk::End) —

    The new Header chunk instance with the variables set to the values according to the content.



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# 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

Instance Method Details

- (String) content

Returns the content for this chunk when it gets written to a file, by packing the image information variables into the correct format.

Returns:

  • (String) —

    The 13-byte content for the header chunk.



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# File 'lib/chunky_png/chunk.rb', line 142

def content
  [width, height, depth, color, compression, filtering, interlace].pack('NNC5')
end