I've edited my code & it works, i've devised it in two parts : the first part where i've detected the canny edges rather then use the HoughLines method to detect it automatically, and the 2nd where i've used the HoughLinesBinary method rather than HoughLines with less arguments, here is the code :
Image<Gray, Byte> gray1 = imgProcessed.Convert<Gray, Byte>().PyrDown().PyrUp();
Image<Gray, Byte> cannyGray = gray1.Canny(120, 180);
imgProcessed = cannyGray;
LineSegment2D[] lines = imgProcessed.HoughLinesBinary(
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