title: HoughLines invalid arguments
body: <p>Hi am using <strong>HoughLines Method</strong> to detect lines from a camera, i've filtered my image "imgProcessed" using <strong>ROI</strong> it means getting just the black objects to make the tracking simple, then when i intend to use the HoughLines method it gives me an error that my "CannyEdges" has some <strong>invalid arguments</strong>, here's my code :</p>
  
  <pre><code>Image&lt;Gray, Byte&gt; gray = imgProcessed.Convert&lt;Gray, Byte&gt;().PyrDown().PyrUp();
          Gray cannyThreshold = new Gray(180);
          Gray cannyThresholdLinking = new Gray(120);
          Gray circleAccumulatorThreshold = new Gray(120);
          Image&lt;Gray, Byte&gt; cannyEdges = gray.Canny(cannyThreshold, cannyThresholdLinking);
  
  
          LineSegment2D[] lines = imgProcessed.cannyEdges.HoughLines(
                                  cannyThreshold,
                                  cannyThresholdLinking,
                                  1,                  //Distance resolution in pixel-related units
                                  Math.PI / 45.0,     //Angle resolution measured in radians.
                                  50,                 //threshold
                                  100,                //min Line width
                                  1                   //gap between lines
                                  )[0];               //Get the lines from the first channel
  </code></pre>