For issue 5). I ran cross it before and make some changes in itkNeighborhoodAlgorithm.txx. Here is the patch, For 5x5 image with kernel size 3x3, the output of regions list are<br><br>9<br>ImageRegion (0xb8b830)<br> Dimension: 2<br>
Index: [1, 1]<br> Size: [3, 3]<br><br>5<br>ImageRegion (0xb8b870)<br> Dimension: 2<br> Index: [0, 0]<br> Size: [1, 5]<br><br>5<br>ImageRegion (0xb8b8b0)<br> Dimension: 2<br> Index: [4, 0]<br> Size: [1, 5]<br><br>
3<br>ImageRegion (0xb8b8f0)<br> Dimension: 2<br> Index: [1, 0]<br> Size: [3, 1]<br><br>3<br>ImageRegion (0xb8b930)<br> Dimension: 2<br> Index: [1, 4]<br> Size: [3, 1]<br><br><br><br><br><div class="gmail_quote">On Mon, Nov 15, 2010 at 11:37 AM, Dawood Masslawi <span dir="ltr"><<a href="mailto:davoud_zzz@yahoo.com">davoud_zzz@yahoo.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><table border="0" cellpadding="0" cellspacing="0"><tbody><tr><td style="font: inherit;" valign="top">
<div><div class="im"><ul><li>1) If I'm going to do this type of thing:</li><li><br></li><li> IteratorType::OffsetType top = {{0,-1}};</li><li> IteratorType::OffsetType bottom = {{0,1}};</li><li> IteratorType::OffsetType left = {{-1,0}};</li>
<li> IteratorType::OffsetType right = {{1,0}};</li><li><br></li><li>Then get the pixels with:</li><li>iterator[top][0]</li><li><br></li><li>is there an advantage to using the ShapedNeighborhoodIterator over just a NeighborhoodIterator?</li>
</ul></div><div><hr></div></div><div><br></div><div>You can use offsets for both ShapedNeighborhoodIterator and regular </div><div><br></div><div>NeighborhoodIterator, the difference is in performance. A regular </div><div>
<br></div><div>NeighborhoodIterator would need more pixels to form a rectangular </div><div><br></div><div>neighborhood
(which artificially could be considered as a </div><div><br></div><div>"ShapedNeighborhoodIterator" using offsets) but a </div><div><br></div><div>ShapedNeighborhoodIterator would require less pixels in the neighborhood</div>
<div><br></div><div>to form a shaped neighborhood, less pixels mean less memory allocation</div><div><br></div><div>and less boundary checking which could remarkably improve the performance</div><div><br></div><div>specially for large neighborhoods in large and multidimensional images plus,</div>
<div><br></div><div>handling shaped neighborhoods is easier with the ShapedNeighborhoodIterator.</div><div><br></div><div><hr></div><div><br></div><div><div><div><div class="im"><ul><li>2) If I do want to use the ShapedNeighborhood style, is this correct:</li>
<li><br></li><li>IteratorType::IndexListType::const_iterator indexIterator =
iterator.GetActiveIndexList().begin();</li><li> while (indexIterator != iterator.GetActiveIndexList().end())</li><li> {</li><li> std::cout << (int)iterator[*indexIterator][0] << " ";</li>
<li> ++indexIterator;</li><li> }</li></ul><div><br></div></div><div><hr>Yes, the following is also a good practice:</div><div><br></div><div><div>IteratorType::ConstIterator ci;</div><div><br></div><div><span style="white-space: pre-wrap;"> </span> for (ci = iterator.Begin(); ci != iterator.End(); ci++)</div>
<div><br></div><div><span style="white-space: pre-wrap;"> </span> { </div><div><br></div><div> std::cout << ci.get() << std::endl;</div><div><br></div><div>
}</div><div><br></div><div><hr><br></div></div></div><div><div class="im"><ul><li>3) If I loop over the ActiveIndexList using the FaceCalculator, is the idea that in all regions except the 0th region I need to do something like:</li>
<li><br></li><li>IteratorType::IndexListType::const_iterator indexIterator = iterator.GetActiveIndexList().begin();</li><li> while (indexIterator != iterator.GetActiveIndexList().end())</li><li> {</li><li> bool valid;</li>
<li> iterator.GetPixel(*indexIterator,valid);</li><li> if(valid) { do something }</li><li> ++indexIterator;</li><li> }</li><li><br></li><li>Alternatively, I could use 4 separate loops (one for each face region) where I know which neighbor isn't valid. I would have to modify the ActiveIndexList to reflect this missing pixel before each
loop.</li></ul></div><div><hr><br></div><div>Usually for neither of face calculator or neighborhood iterator you need to perform </div><div><br></div><div>the boundary check yourself (notice that the iterator itself has to iterate over the </div>
<div><br></div><div>boundary to check for its validity), the face calculator splits the image into boundary </div><div><br></div><div>and non-boundary regions for the iterator to not to check for all of the pixels and </div>
<div><br></div><div>only perform the boundary checking for pixels in the face region (pixels with distance </div><div><br></div><div>from the image boundary equal or less than the neighborhood radius). This would also</div>
<div><br></div><div> improve the performance specially for large datasets.</div><div><br></div><div><hr></div></div><div class="im"><div><ul><li>4) I believe </li><li>iterator[top][0]</li><li>is equivalent to but faster than iterator.GetPixel(top). Is
this correct?</li></ul></div></div><div><hr>I'm not sure about this since I haven't seen a significant performance difference.</div><div><br></div><div><ul><li><hr></li><div class="im"><li>5) Am I correct that the face calculator returns overlapping regions? If I use a 5x5 image with a 3x3 kernel, it returns regions of size</li>
<li>9</li><li>5</li><li>5</li><li>5</li><li>5</li><li><br></li><li>totaling 29, when there are only 25 pixels. I don't see any functions to turn on/off this overlap. How is this usually handled?</li></div></ul><div><hr>
<br></div><div>To the best of my knowledge this is still an unsolved issue which was brought up </div><div><br></div><div>by other users in the list as well. Usually the face calculator assumes that the </div><div><br></div>
<div>face region is far smaller than the non-boundary region which could be an issue </div><div><br></div><div>for small images or very large
neighborhoods.</div><div><br></div><div><br></div><div>Regards,</div><div><br></div><div>Dawood</div></div></div></div></td></tr></tbody></table><br>
<br>_____________________________________<br>
Powered by <a href="http://www.kitware.com" target="_blank">www.kitware.com</a><br>
<br>
Visit other Kitware open-source projects at<br>
<a href="http://www.kitware.com/opensource/opensource.html" target="_blank">http://www.kitware.com/opensource/opensource.html</a><br>
<br>
Kitware offers ITK Training Courses, for more information visit:<br>
<a href="http://www.kitware.com/products/protraining.html" target="_blank">http://www.kitware.com/products/protraining.html</a><br>
<br>
Please keep messages on-topic and check the ITK FAQ at:<br>
<a href="http://www.itk.org/Wiki/ITK_FAQ" target="_blank">http://www.itk.org/Wiki/ITK_FAQ</a><br>
<br>
Follow this link to subscribe/unsubscribe:<br>
<a href="http://www.itk.org/mailman/listinfo/insight-users" target="_blank">http://www.itk.org/mailman/listinfo/insight-users</a><br>
<br></blockquote></div><br>