Class: Branding::PNG

Inherits:
Object
  • Object
show all
Defined in:
lib/branding/png.rb

Overview

This is a simple PNG decoder, inspired and adapted from ChunkyPNG

Defined Under Namespace

Classes: Filter, Imagedata

Constant Summary collapse

SIGNATURE = 
[137, 80, 78, 71, 13, 10, 26, 10].pack('C8').force_encoding('BINARY')

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(io) ⇒ PNG

Returns a new instance of PNG.



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# File 'lib/branding/png.rb', line 159

def initialize(io)
  signature = io.read(SIGNATURE.length)
  raise 'Signature mismatch' unless signature == SIGNATURE

  @data = ''

  until io.eof?
    type, content = read_chunk(io)

    case type
    when 'IHDR'
      fields = content.unpack('NNC5')
      @width, @height, @depth, @color, @compression, @filtering, @interlace = fields

    when 'IDAT'
      @data << content
    end
  end

  unless depth == 8
    raise NotImplementedError, 'only supporting 8bit color depth'
  end

  unless color == 2 || color == 6
    raise NotImplementedError, 'only supporting true color, with or without alpha'
  end

  unless filtering == 0
    raise NotImplementedError, 'does not supporting filtering'
  end

  unless compression == 0
    raise NotImplementedError, 'only supporting deflate compression'
  end
end

Instance Attribute Details

#color ⇒ Object (readonly)

Returns the value of attribute color.



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# File 'lib/branding/png.rb', line 9

def color
  @color
end

#compression ⇒ Object (readonly)

Returns the value of attribute compression.



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# File 'lib/branding/png.rb', line 9

def compression
  @compression
end

#depth ⇒ Object (readonly)

Returns the value of attribute depth.



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# File 'lib/branding/png.rb', line 9

def depth
  @depth
end

#filtering ⇒ Object (readonly)

Returns the value of attribute filtering.



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# File 'lib/branding/png.rb', line 9

def filtering
  @filtering
end

#height ⇒ Object (readonly)

Returns the value of attribute height.



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# File 'lib/branding/png.rb', line 9

def height
  @height
end

#interlace ⇒ Object (readonly)

Returns the value of attribute interlace.



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# File 'lib/branding/png.rb', line 9

def interlace
  @interlace
end

#width ⇒ Object (readonly)

Returns the value of attribute width.



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# File 'lib/branding/png.rb', line 9

def width
  @width
end

Class Method Details

.from_file(path) ⇒ Object 



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# File 'lib/branding/png.rb', line 155

def self.from_file(path)
  new(File.open(path, 'rb'))
end

Instance Method Details

#color_channels ⇒ Object

the number of color channels. Not the PNG “color mode”



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# File 'lib/branding/png.rb', line 205

def color_channels
  color == 2 ? 3 : 4
end

#pixels ⇒ Object 



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# File 'lib/branding/png.rb', line 195

def pixels
  if block_given?
    imagedata.each_pixel
  else
    imagedata.enum_for(:each_pixel).to_a
  end
end