Class: ZPNG::Chunk::IHDR

Inherits:
ZPNG::Chunk show all
Defined in:
lib/zpng/chunk.rb

Direct Known Subclasses

BMP::BmpHdrPseudoChunk

Constant Summary collapse

PALETTE_USED = 
1
COLOR_USED = 
2
ALPHA_USED = 
4
SAMPLES_PER_COLOR =

Each pixel is an R,G,B triple, followed by an alpha sample.

{
  COLOR_GRAYSCALE  => 1,
  COLOR_RGB        => 3,
  COLOR_INDEXED    => 1,
  COLOR_GRAY_ALPHA => 2,
  COLOR_RGBA       => 4
}
ALLOWED_DEPTHS =

www.w3.org/TR/PNG/#table111

{
  COLOR_GRAYSCALE  => [ 1, 2, 4, 8, 16 ],
  COLOR_RGB        => [          8, 16 ],
  COLOR_INDEXED    => [ 1, 2, 4, 8     ],
  COLOR_GRAY_ALPHA => [          8, 16 ],
  COLOR_RGBA       => [          8, 16 ],
}
FORMAT = 
'NNC5'

Instance Attribute Summary collapse

Attributes inherited from ZPNG::Chunk

#crc, #data, #idx, #size, #type

Instance Method Summary collapse

Methods inherited from ZPNG::Chunk

#crc_ok?, #export, #fix_crc!, from_stream

Methods included from DeepCopyable

#deep_copy

Constructor Details

#initialize(x) ⇒ IHDR

Returns a new instance of IHDR.



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# File 'lib/zpng/chunk.rb', line 110

def initialize x
  super
  vars = %w'width height depth color compression filter interlace' # order is important
  if x.respond_to?(:read)
    # IO
  elsif x.respond_to?(:[])
    # Hash
    vars.each{ |k| instance_variable_set "@#{k}", x[k.to_sym] }

    raise "[!] width not set" unless @width
    raise "[!] height not set" unless @height

    # allow easier image creation like
    # img = Image.new :width => 16, :height => 16, :bpp => 4, :color => false
    # img = Image.new :width => 16, :height => 16, :bpp => 1, :color => true
    # img = Image.new :width => 16, :height => 16, :bpp => 32
    if x[:bpp]
      unless [true,false,nil].include?(@color)
        raise "[!] :color must be either 'true' or 'false' when :bpp is set"
      end
      if @depth
        raise "[!] don't use :depth when :bpp is set"
      end
      @color, @depth = case x[:bpp]
        when 1,2,4,8; [ @color ? COLOR_INDEXED : COLOR_GRAYSCALE,  x[:bpp] ]
        when 16;
          raise "[!] I don't know how to make COLOR 16 bpp PNG. do you?" if @color
          [ COLOR_GRAY_ALPHA, 8 ]
        when 24;      [ COLOR_RGB,  8 ]
        when 32;      [ COLOR_RGBA, 8 ]
        else
          raise "[!] unsupported bpp=#{x[:bpp].inspect}"
        end
    end

    @color       ||= COLOR_RGBA
    @depth       ||= 8
    @compression ||= 0
    @filter      ||= 0
    @interlace   ||= 0

    unless ALLOWED_DEPTHS[@color].include?(@depth)
      raise "[!] invalid color mode (#{@color.inspect}) / bit depth (#{@depth.inspect}) combination"
    end
  end
  if data
    data.unpack(FORMAT).each_with_index do |value,idx|
      instance_variable_set "@#{vars[idx]}", value
    end
  end
end

Instance Attribute Details

#color ⇒ Object

Returns the value of attribute color.



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# File 'lib/zpng/chunk.rb', line 74

def color
  @color
end

#compression ⇒ Object

Returns the value of attribute compression.



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# File 'lib/zpng/chunk.rb', line 74

def compression
  @compression
end

#depth ⇒ Object

Returns the value of attribute depth.



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# File 'lib/zpng/chunk.rb', line 74

def depth
  @depth
end

#filter ⇒ Object

Returns the value of attribute filter.



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# File 'lib/zpng/chunk.rb', line 74

def filter
  @filter
end

#height ⇒ Object

Returns the value of attribute height.



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# File 'lib/zpng/chunk.rb', line 74

def height
  @height
end

#interlace ⇒ Object

Returns the value of attribute interlace.



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# File 'lib/zpng/chunk.rb', line 74

def interlace
  @interlace
end

#width ⇒ Object

Returns the value of attribute width.



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# File 'lib/zpng/chunk.rb', line 74

def width
  @width
end

Instance Method Details

#alpha_used? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/zpng/chunk.rb', line 183

def alpha_used?
  (@color & ALPHA_USED) != 0
end

#bpp ⇒ Object

bits per pixel



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# File 'lib/zpng/chunk.rb', line 167

def bpp
  SAMPLES_PER_COLOR[@color] * depth
end

#color_used? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/zpng/chunk.rb', line 171

def color_used?
  (@color & COLOR_USED) != 0
end

#export_data ⇒ Object 



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# File 'lib/zpng/chunk.rb', line 162

def export_data
  [@width, @height, @depth, @color, @compression, @filter, @interlace].pack(FORMAT)
end

#grayscale? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/zpng/chunk.rb', line 175

def grayscale?
  !color_used?
end

#inspect(verbosity = 10) ⇒ Object 



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# File 'lib/zpng/chunk.rb', line 187

def inspect verbosity = 10
  vars = instance_variables - [:@type, :@crc, :@data, :@size]
  vars -= [:@idx] if verbosity <= 0
  super.sub(/ *>$/,'') + ", " +
    vars.sort.map{ |var| "#{var.to_s.tr('@','')}=#{instance_variable_get(var)}" }.
    join(", ") + ">"
end

#palette_used? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/zpng/chunk.rb', line 179

def palette_used?
  (@color & PALETTE_USED) != 0
end