class Prawn::Images::JPG

A convenience class that wraps the logic for extracting the parts of a JPG image that we need to embed them in a PDF

Constants

JPEG_APP_BLOCKS
JPEG_SOF_BLOCKS

Attributes

bits[R]
channels[R]
height[R]
scaled_height[RW]
scaled_width[RW]
width[R]

Public Class Methods

new(data) click to toggle source

Process a new JPG image

:data

A binary string of JPEG data

# File lib/prawn/images/jpg.rb, line 26
def initialize(data)
  data = StringIO.new(data.dup)

  c_marker = "\xff" # Section marker.
  data.read(2)   # Skip the first two bytes of JPEG identifier.
  loop do
    marker, code, length = data.read(4).unpack('aan')
    raise "JPEG marker not found!" if marker != c_marker

    if JPEG_SOF_BLOCKS.include?(code)
      @bits, @height, @width, @channels = data.read(6).unpack("CnnC")
      break
    end

    buffer = data.read(length - 2)
  end
end