title: Libpng, Palette png with alpha or not?
body: <p>How to know if palette png is with alpha or not?
  I get information about the image <code>png_get_IHDR</code></p>
  
  <p>After that i look at <code>color_type - PNG_COLOR_TYPE_PALETTE</code></p>
  
  <p>But i can't find how to know if this png image has alpha channel or not.</p>