[sift] Remove the narrow Gaussian filter option "opencv"

OpenCV used quite narrow Gaussian filters when PopSift was first written.
This computation was adopted for compatibility reasons. The other modes are more accurate.

Author: Carsten Griwodz

src/popsift/gauss_filter.cu

@@ -273,8 +273,6 @@ int GaussInfo::getSpan( float sigma ) const
         return GaussInfo::vlFeatSpan( sigma );
     case Config::VLFeat_Relative :
         return GaussInfo::vlFeatRelativeSpan( sigma );
-    case Config::OpenCV_Compute :
-        return GaussInfo::openCVSpan( sigma );
     case Config::Fixed9 :
         return 5;
     case Config::Fixed15 :
@@ -306,15 +304,6 @@ int GaussInfo::vlFeatRelativeSpan( float sigma )
     return spn;
 }
 
-__host__
-int GaussInfo::openCVSpan( float sigma )
-{
-    int span = int( roundf( 2.0f * 4.0f * sigma + 1.0f ) ) | 1;
-    span >>= 1;
-    span  += 1;
-    return std::min<int>( span, GAUSS_ALIGN - 1 );
-}
-
 template<int LEVELS>
 __host__
 void GaussTable<LEVELS>::clearTables( )

src/popsift/gauss_filter.h

@@ -100,9 +100,6 @@ struct GaussInfo
 
     __host__
     static int vlFeatRelativeSpan( float sigma );
-
-    __host__
-    static int openCVSpan( float sigma );
 };
 
 extern __device__ __constant__ GaussInfo d_gauss;

src/popsift/sift_conf.cu

@@ -111,8 +111,6 @@ void Config::setGaussMode( const std::string& m )
         setGaussMode( Config::VLFeat_Relative );
     else if( m == "vlfeat-direct" )
         setGaussMode( Config::VLFeat_Relative_All );
-    else if( m == "opencv" )
-        setGaussMode( Config::OpenCV_Compute );
     else if( m == "fixed9" )
         setGaussMode( Config::Fixed9 );
     else if( m == "fixed15" )
@@ -134,7 +132,6 @@ const char* Config::getGaussModeUsage( )
         "vlfeat (default), "
         "vlfeat-hw-interpolated, "
         "vlfeat-direct, "
-        "opencv, "
         "fixed9, "
         "fixed15, "
         "relative (synonym for vlfeat-hw-interpolated)";

src/popsift/sift_conf.h

@@ -40,7 +40,6 @@ struct Config
         VLFeat_Compute,
         VLFeat_Relative,
         VLFeat_Relative_All,
-        OpenCV_Compute,
         Fixed9,
         Fixed15
     };