| void Impala::Core::KeyPoint::Sift::ComputeGradientField | ( | ) | [inline] |
Definition at line 113 of file Sift.h.
References ILOG_INFO, mGradAng, mGradMag, mLevelCnt, mOctaveCnt, mOctaves, Normalize(), Impala::Core::Array::Set(), Impala::Core::Array::SetVal(), and Impala::Application::DemoCamera2d::sigma.
Referenced by ExtractDescriptors().
00113 { 00114 double H[4]; 00115 double G[2]; 00116 double S[2]; 00117 00118 ILOG_INFO("Computing gradient field"); 00119 00120 //For every level, construct the gradient magnitude and angle map 00121 for(int o=0;o<mOctaveCnt;o++){ 00122 for(int l=0;l<mLevelCnt;l++) 00123 { 00124 Array2dScalarReal64* L = mOctaves->GetOctave(o,l); 00125 Set(mGradMag[o*mLevelCnt+l],L); 00126 SetVal(mGradMag[o*mLevelCnt+l],0); 00127 Set(mGradAng[o*mLevelCnt+l],mGradMag[o*mLevelCnt+l]); 00128 //dd stands for derivative distance.. 00129 int dd; 00130 //The sigma to be calculated in the gradient comes from 00131 //the difference of gaussians, for which peaks are analysed 00132 //in the sigma neighborhood. because of these two shifts, we 00133 //have to use l+2 00134 Real64 sigma=mOctaves->GetSigma(o,l+2); 00136 // If resampling is enabled, we have already reduced 00137 // the scale by two at every octave(doubling of sigma). 00138 // Therefore the derivative is the immediate neighbors. 00139 // 00140 // Otherwise jump as much as 1 sigma for a derivative, 00141 // since the images are not scaled down as well. 00142 if(mOctaves->IsResamplingEnabled()) 00143 dd=1; 00144 else 00145 dd=sigma; 00146 00147 for(int i=dd;i<L->CW()-dd;i++){ 00148 for(int j=dd;j<L->CH()-dd;j++){ 00149 //this is the first derivative wrt. x 00150 //[ -1 0 1 ] 00151 G[0] = L->Value(i+dd,j) - L->Value(i-dd,j); 00152 00153 //this is the first derivative wrt. y 00154 G[1] = L->Value(i,j+dd) - L->Value(i,j-dd); 00155 00156 mGradMag[o*mLevelCnt+l]->SetValue(sqrt(G[0]*G[0]+G[1]*G[1]) 00157 ,i,j); 00158 mGradAng[o*mLevelCnt+l]->SetValue(atan(G[1]/G[0]),i,j); 00159 00160 00161 } 00162 } 00163 /* 00164 ILOG_DEBUG("Octave("<<o<<","<<l<<") : (" 00165 <<PixMin( mGradMag[o*mLevels+l]) <<"," 00166 <<PixMax( mGradMag[o*mLevels+l]) <<") (" 00167 <<PixMin( mGradAng[o*mLevels+l]) <<"," 00168 <<PixMax( mGradAng[o*mLevels+l]) <<")");*/ 00169 Normalize(mGradMag[o*mLevelCnt+l]); 00170 00171 } 00172 } 00173 }
Here is the call graph for this function:
