I did the following changes in this part of my programme.. now the refereence error is removed but its showing me another error :<br><br>def ComputeClasses(data):<br>    radius = .5 <br>    points = []<br>    for cy in xrange(0, data.height):<br>
        for cx in xrange(0, data.width): <br>                                        <br>            if data[cy,cx] == (0.0,0.0,0.0):<br>                continue<br>            else : <br>                centre = data[cy, cx]<br>
                print centre<br>                points.append(centre)    <br>                <br><br>            change = True  <br><br>            while change: <br>                <br>                for ring_number in xrange(1, 1000): <br>
                    change = False<br>                    new_indices = GenerateRing(cx, cy, ring_number) <br>                                                                    <br>                    for idx in new_indices:<br>
                        point = data[idx[0], idx[1]] <br>                   <br>                        if point == (0.0, 0.0, 0.0 ):  <br>                          continue<br>                        else: <br>                                    <br>
                            dist = distance(centre, point)<br>                            if  dist < radius :<br>                                print point <br>                                points.append(point)<br>                                change = True<br>
                                print change<br>                  <br>                <br>                break <br>        <br>            <br>            print points <br><br><br>ERROR :<br><br>Traceback (most recent call last):<br>
  File "Z:/modules/classification1.py", line 71, in <module><br>    ComputeClasses(data)<br>  File "Z:/modules/classification1.py", line 47, in ComputeClasses<br>    point = data[idx[0], idx[1]]<br>
error: index is out of range<br><br>What is meant by this statement ' Index out of range ' ? Does it mean that my range 1, 1000 is exceeded ??<br><br><br><div class="gmail_extra"><br></div>