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</o:shapelayout></xml><![endif]--></head><body lang=ES link=blue vlink=purple><div class=WordSection1><h1 align=center style='text-align:center'><span lang=EN-US>Inaccuracy in <i>fftw</i> calculation<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>I am calculating the <i>fft</i> of an image which pixels are double with the FFTW library, for that purpose i am using the library fftw(</span><a href="http://www.fftw.org/"><span lang=EN-US>http://www.fftw.org/</span></a><span lang=EN-US>) library in Visual Studio 2008 and using ITK.<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>When I calculate the fft from a double pointer, with the method ‘<i>fftw_plan_dft_c2r_</i>2d’, it makes the calculation but introducing inaccuracy, it is around +- 0.5…<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>I don’t really know what is wrong, maybe the spacing between pixels? The type of the data used? Did someone have this problem or something similar before?<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Many thanks in advanced.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>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 Señal)[ </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>