Class: ZIMG::PNG::Chunk::IHDR

Inherits:
ZIMG::PNG::Chunk show all
Defined in:
lib/zimg/png/chunks.rb

Direct Known Subclasses

BMP::BmpHdrPseudoChunk

Constant Summary collapse

SIZE = 
13
FORMAT = 
"NNC5"
PALETTE_USED = 
1
COLOR_USED = 
2
ALPHA_USED = 
4
SAMPLES_PER_COLOR = 
{
  COLOR_GRAYSCALE => 1,
  COLOR_RGB => 3,
  COLOR_INDEXED => 1,
  COLOR_GRAY_ALPHA => 2,
  COLOR_RGBA => 4,
}.freeze
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],
}.freeze

Constants inherited from ZIMG::PNG::Chunk

KNOWN_TYPES, VALID_SIZE_RANGE

Instance Attribute Summary collapse

Attributes inherited from ZIMG::PNG::Chunk

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

Instance Method Summary collapse

Methods inherited from ZIMG::PNG::Chunk

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

Methods included from DeepCopyable

#deep_copy

Methods inherited from Chunk

#cli_color

Constructor Details

#initialize(x) ⇒ IHDR

Returns a new instance of IHDR.



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# File 'lib/zimg/png/chunks.rb', line 132

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
      raise "[!] don't use :depth when :bpp is set" if @depth

      @color, @depth = case x[:bpp]
                       when 1, 2, 4, 8 then [@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 then      [COLOR_RGB,  8]
                       when 32 then      [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
  return unless data

  data.unpack(FORMAT).each_with_index do |value, idx|
    instance_variable_set "@#{vars[idx]}", value
  end
end

Instance Attribute Details

#color ⇒ Object

Returns the value of attribute color.



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# File 'lib/zimg/png/chunks.rb', line 106

def color
  @color
end

#compression ⇒ Object

Returns the value of attribute compression.



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# File 'lib/zimg/png/chunks.rb', line 106

def compression
  @compression
end

#depth ⇒ Object

Returns the value of attribute depth.



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# File 'lib/zimg/png/chunks.rb', line 106

def depth
  @depth
end

#filter ⇒ Object

Returns the value of attribute filter.



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# File 'lib/zimg/png/chunks.rb', line 106

def filter
  @filter
end

#height ⇒ Object

Returns the value of attribute height.



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# File 'lib/zimg/png/chunks.rb', line 106

def height
  @height
end

#interlace ⇒ Object

Returns the value of attribute interlace.



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# File 'lib/zimg/png/chunks.rb', line 106

def interlace
  @interlace
end

#width ⇒ Object

Returns the value of attribute width.



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# File 'lib/zimg/png/chunks.rb', line 106

def width
  @width
end

Instance Method Details

#alpha_used? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/zimg/png/chunks.rb', line 206

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

#bpp ⇒ Object

bits per pixel



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# File 'lib/zimg/png/chunks.rb', line 189

def bpp
  spc = SAMPLES_PER_COLOR[@color]
  spc ? spc * depth : nil
end

#color_used? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/zimg/png/chunks.rb', line 194

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

#export_data ⇒ Object 



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# File 'lib/zimg/png/chunks.rb', line 184

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

#grayscale? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/zimg/png/chunks.rb', line 198

def grayscale?
  !color_used?
end

#inspect(verbosity = 10) ⇒ Object 



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# File 'lib/zimg/png/chunks.rb', line 210

def inspect(verbosity = 10)
  vars = instance_variables - %i[@type @crc @data @size]
  vars -= [:@idx] if verbosity <= 0
  info = vars.map { |var| ", #{var.to_s.tr("@", "")}=#{instance_variable_get(var)}" }.join
  "#{super.chop.rstrip}#{info} >"
end

#palette_used? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/zimg/png/chunks.rb', line 202

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