title: ImageMagick sampling factor
body: <p>I have been using ImageMagick command line tool for jpeg compression of the images. However, I'm trying to understand the role of sampling factor. It says the sampling factor is used to specify the block size i.e. 8x8 or 16x16. However, I can't find the default values used if I omit this parameter. </p>
  
  <p>Also, I tried fetching properties of an image by using the following command:</p>
  
  <p>identify -verbose image.jpg</p>
  
  <p>It shows sampling factor values as 1x1, 1x1, 1x1. What does it mean? Either it should be 8x8 or 16x16 or 32x32....</p>
  
  <p>Could anyone please give me an idea where to find these details?</p>