title: Gdal substract 1 bit raster gives me hard time
body: <p>I want to use <code>gdal_calc</code> to subtract one file from another. It works, but I get the wrong result all the time no matter what command line i try.
  For your understanding I created 3 files.</p>
  <p>Picture A:</p>
  <p><img src="https://i.stack.imgur.com/P2fJv.jpg" alt="Picture A" /></p>
  <p>Picture B:</p>
  <p><img src="https://i.stack.imgur.com/f7fHa.jpg" alt="Picture B" /></p>
  <p>Picture C:</p>
  <p><img src="https://i.stack.imgur.com/FgJCU.jpg" alt="Result" /></p>
  <p>As you can see I always get the overlap as result but I need the other part.</p>
  <p>Desired Result:</p>
  <p><img src="https://i.stack.imgur.com/QiOJH.jpg" alt="result I want." /></p>
  <p><code>gdal_calc.py -A pica.tif -B picb.tif --outfile=result.tif --calc=&quot;A-B&quot;</code></p>
  <p>Change the line to</p>
  <p><code>gdal_calc.py -A pica.tif -B picb.tif --outfile=result.tif --calc=&quot;B-A&quot;</code></p>
  <p>or swap filenames doesn't work? I always get the same result.
  I also delete the output file before trying new stuff so thats not the problem that I always look at the same file.</p>