Ruby snippet to extract the thumbnail .png enbeded in a .skp (SketchUp) file.

extract_png.rb

# with a lot of help from Adam on comp.lang.ruby

def extract_chunk(input, output)
  lenword = input.read(4)
  length = lenword.unpack('N')[0]
  type = input.read(4)
  data = length>0 ? input.read(length) : ""
  crc = input.read(4)
  return nil if length<0 || !(('A'..'z')===type[0,1])
  #return nil if validate_crc(type+data, crc)
  output.write lenword
  output.write type
  output.write data
  output.write crc
  return type
end

def extract_png(input, output)
  hdr = input.read(8)
  raise "Not a PNG File" if hdr[0,4]!= "\211PNG"
  raise "file not in binary mode" if hdr[4,4]!="\r\n\032\n"
  output.write(hdr)
  loop do
    chunk_type = extract_chunk(input,output)
    #p chunk_type
    break if  chunk_type.nil? || chunk_type == 'IEND'
  end
end

files = Dir["*.skp"]
files.each do |f|
  fp = File.new(f,"rb")
  fn = File.basename(f, ".skp")
  m = /\211PNG/.match(fp.read)
  raise "no PNG" if !m
  fp.seek(m.begin(0)) 
  ofp = File.new("#{fn}.png","wb")
  extract_png(fp,ofp) 
  fp.close
  ofp.close
end