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</o:shapelayout></xml><![endif]--></head><body lang=ES link=blue vlink=purple><div class=WordSection1><h1><span lang=EN-US style='font-family:"Calibri","sans-serif"'>Erroneous Results calculating the gradient of an image with ITK<o:p></o:p></span></h1><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:12.0pt;font-family:"Times New Roman","serif"'>In the header file, I declare all of this types, The “Gradient ImageFilter” is for calculate the gradient of a 2D image, and the “VectorIndexSelectionCastImageFilter” is for selecting the ’x’ and ‘y’ component of the gradient calculating, due to the fact that the result of computing th gradient is a vector image.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:12.0pt;font-family:"Times New Roman","serif"'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#0070C0'>typedef double </span><span lang=EN-US> operatorValueType;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#0070C0'>typedef double </span><span lang=EN-US> outputValueType;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#0070C0'>typedef double </span><span lang=EN-US> InputPixelType;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#0070C0'>typedef </span><span lang=EN-US>itk::Image<InputPixelType, 2> InputImageType;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#0070C0'>typedef </span><span lang=EN-US>itk::GradientImageFilter< InputImageType, operatorValueType, outputValueType> GradientFilterType;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#00B050'> //for extracting a scalar from the vector image<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#0070C0'>typedef double</span><span lang=EN-US> OutputPixelTypeImage;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#0070C0'>typedef double</span><span lang=EN-US> ComponentType;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#0070C0'>typedef </span><span lang=EN-US>itk::CovariantVector<ComponentType,2> OutputPixelType;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#0070C0'>typedef </span><span lang=EN-US>itk::Image <OutputPixelType, 2> OutputImageType;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#0070C0'>typedef </span><span lang=EN-US>itk::VectorIndexSelectionCastImageFilter<OutputImageType,InputImageType> SelectionFilterType; <span style='color:#00B050'>// < intputType , outputType></span><o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:12.0pt;font-family:"Times New Roman","serif"'>After the declarations, the main part of interest of the code is below:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>GradientFilterType::Pointer gradientFilter = GradientFilterType::New();<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>gradientFilter->SetInput(T_g->GetOutput()); <span style='color:#00B050'>// From T_g (is a reader) comes the image</span><o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>gradientFilter->Update();<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>SelectionFilterType::Pointer componentExtractor_x = SelectionFilterType::New();<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>SelectionFilterType::Pointer componentExtractor_y = SelectionFilterType::New();<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>componentExtractor_x->SetIndex(0);<span style='color:#00B050'>// x component of the gradient</span><o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>componentExtractor_y->SetIndex(1);<span style='color:#00B050'>// y component of the gradient<o:p></o:p></span></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>componentExtractor_x->SetInput(gradientFilter->GetOutput());<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>componentExtractor_y->SetInput(gradientFilter->GetOutput());<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>componentExtractor_x->Update();<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>componentExtractor_y->Update();<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>It seems that everything works fine, but the problem is that when I read the image and I compare it with the calculation of the gradient in Matlab (which I assume to be correct) the results are completely different…Anyone has used before the “VectorIndexSelectionCastImageFilter” and see something strange? Or in the process of calculating the gradient?<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>Thanks so much!<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US> </span>Antonio Gómez Barquero<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span lang=ES-TRAD style='font-size:8.0pt;mso-fareast-language:ES'>Ingeniero de Telecomunicaciones -Becario Investigador asociado a Actividades de I+D+I <o:p></o:p></span></p><p class=MsoNormal><span lang=ES-TRAD style='font-size:8.0pt;mso-fareast-language:ES'>GTTS ( Grupo de Tratamiento y Teoría de la Seńal)[ </span><span style='font-size:8.0pt;mso-fareast-language:ES'><a href="http://gtts.upct.es/"><span style='color:blue'>http://gtts.upct.es/</span></a></span><span lang=ES-TRAD style='font-size:8.0pt;mso-fareast-language:ES'>]<o:p></o:p></span></p><p class=MsoNormal><span lang=ES-TRAD style='font-size:8.0pt;mso-fareast-language:ES'>UPCT (Universidad Politécnica de Cartagena)[ </span><span style='font-size:8.0pt;mso-fareast-language:ES'><a href="http://www.upct.es/"><span style='color:blue'>http://www.upct.es/</span></a>]</span><span lang=ES-TRAD style='font-size:8.0pt;mso-fareast-language:ES'><o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>