title: What is the baseline architecture of JPEG?
body: <p>I sometimes keep reading that baseline is used synonymously with the sequencial compression mode of a JPEG and I am confused by that. </p>
  
  <p>On the <a href="https://de.wikipedia.org/wiki/JPEG#.C3.9Cbersicht_und_Standards" rel="nofollow">german wiki page for JPEG</a> there are listed four main compression modes:</p>
  
  <ul>
  <li>sequential</li>
  <li>progressive</li>
  <li>hierarchical</li>
  <li>lossless </li>
  </ul>
  
  <p>Searching for "baseline" on that page returns zero hits. </p>
  
  <p>Other sources call it baseline standard, baseline sequential and compare it to progressive. On another page about that topic I have found a comparison between baseline sequential and baseline progressive. </p>
  
  <p><strong>Can somebody explain me what "baseline" actually is?</strong></p>
  
  <p>I thought that baseline is the name of an architecture for sequential, progressive and hierarchical JPEG images which is a bare minimum of subprocesses (downsampling, DCT, etc.) a program (for example image viewer) has to implement such that he is able to view images of those modes. I have a book that states:</p>
  
  <blockquote>
    <p>There are two main modes: lossy (also called baseline) and lossless (which typically produces compression ratios of around 0.5).</p>
  </blockquote>