train_cascade 源码阅读之Haar特征

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下面片段是生成用于在积分图中的矩形块的坐标,Feature类中存的是在积分图矩阵中的初始偏移量,矩形的左上角坐标和宽高,以及是否旋转。不同类型的Haar特征已经在代码中体现的很明确了,故不赘述。
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  1. <span style="font-size:14px;">void CvHaarEvaluator::generateFeatures()  
  2. {  
  3.     int mode = ((const CvHaarFeatureParams*)((CvFeatureParams*)featureParams))->mode;  
  4.     int offset = winSize.width + 1;  
  5.     forint x = 0; x < winSize.width; x++ )  
  6.     {  
  7.         forint y = 0; y < winSize.height; y++ )  
  8.         {  
  9.             forint dx = 1; dx <= winSize.width; dx++ )  
  10.             {  
  11.                 forint dy = 1; dy <= winSize.height; dy++ )  
  12.                 {  
  13.                     // haar_x2  
  14.                     if ( (x+dx*2 <= winSize.width) && (y+dy <= winSize.height) )  
  15.                     {  
  16.                         features.push_back( Feature( offset, false,  
  17.                             x,    y, dx*2, dy, -1,  
  18.                             x+dx, y, dx  , dy, +2 ) );  
  19.                     }  
  20.                     // haar_y2  
  21.                     if ( (x+dx <= winSize.width) && (y+dy*2 <= winSize.height) )  
  22.                     {  
  23.                         features.push_back( Feature( offset, false,  
  24.                             x,    y, dx, dy*2, -1,  
  25.                             x, y+dy, dx, dy,   +2 ) );  
  26.                     }  
  27.                     // haar_x3  
  28.                     if ( (x+dx*3 <= winSize.width) && (y+dy <= winSize.height) )  
  29.                     {  
  30.                         features.push_back( Feature( offset, false,  
  31.                             x,    y, dx*3, dy, -1,  
  32.                             x+dx, y, dx  , dy, +3 ) );  
  33.                     }  
  34.                     // haar_y3  
  35.                     if ( (x+dx <= winSize.width) && (y+dy*3 <= winSize.height) )  
  36.                     {  
  37.                         features.push_back( Feature( offset, false,  
  38.                             x, y,    dx, dy*3, -1,  
  39.                             x, y+dy, dx, dy,   +3 ) );  
  40.                     }  
  41.                     if( mode != CvHaarFeatureParams::BASIC )  
  42.                     {  
  43.                         // haar_x4  
  44.                         if ( (x+dx*4 <= winSize.width) && (y+dy <= winSize.height) )  
  45.                         {  
  46.                             features.push_back( Feature( offset, false,  
  47.                                 x,    y, dx*4, dy, -1,  
  48.                                 x+dx, y, dx*2, dy, +2 ) );  
  49.                         }  
  50.                         // haar_y4  
  51.                         if ( (x+dx <= winSize.width ) && (y+dy*4 <= winSize.height) )  
  52.                         {  
  53.                             features.push_back( Feature( offset, false,  
  54.                                 x, y,    dx, dy*4, -1,  
  55.                                 x, y+dy, dx, dy*2, +2 ) );  
  56.                         }  
  57.                     }  
  58.                     // x2_y2  
  59.                     if ( (x+dx*2 <= winSize.width) && (y+dy*2 <= winSize.height) )  
  60.                     {  
  61.                         features.push_back( Feature( offset, false,  
  62.                             x,    y,    dx*2, dy*2, -1,  
  63.                             x,    y,    dx,   dy,   +2,  
  64.                             x+dx, y+dy, dx,   dy,   +2 ) );  
  65.                     }  
  66.                     if (mode != CvHaarFeatureParams::BASIC)  
  67.                     {  
  68.                         if ( (x+dx*3 <= winSize.width) && (y+dy*3 <= winSize.height) )  
  69.                         {  
  70.                             features.push_back( Feature( offset, false,  
  71.                                 x   , y   , dx*3, dy*3, -1,  
  72.                                 x+dx, y+dy, dx  , dy  , +9) );  
  73.                         }  
  74.                     }  
  75.                     if (mode == CvHaarFeatureParams::ALL)  
  76.                     {  
  77.                         // tilted haar_x2  
  78.                         if ( (x+2*dx <= winSize.width) && (y+2*dx+dy <= winSize.height) && (x-dy>= 0) )  
  79.                         {  
  80.                             features.push_back( Feature( offset, true,  
  81.                                 x, y, dx*2, dy, -1,  
  82.                                 x, y, dx,   dy, +2 ) );  
  83.                         }  
  84.                         // tilted haar_y2  
  85.                         if ( (x+dx <= winSize.width) && (y+dx+2*dy <= winSize.height) && (x-2*dy>= 0) )  
  86.                         {  
  87.                             features.push_back( Feature( offset, true,  
  88.                                 x, y, dx, 2*dy, -1,  
  89.                                 x, y, dx, dy,   +2 ) );  
  90.                         }  
  91.                         // tilted haar_x3  
  92.                         if ( (x+3*dx <= winSize.width) && (y+3*dx+dy <= winSize.height) && (x-dy>= 0) )  
  93.                         {  
  94.                             features.push_back( Feature( offset, true,  
  95.                                 x,    y,    dx*3, dy, -1,  
  96.                                 x+dx, y+dx, dx,   dy, +3 ) );  
  97.                         }  
  98.                         // tilted haar_y3  
  99.                         if ( (x+dx <= winSize.width) && (y+dx+3*dy <= winSize.height) && (x-3*dy>= 0) )  
  100.                         {  
  101.                             features.push_back( Feature( offset, true,  
  102.                                 x,    y,    dx, 3*dy, -1,  
  103.                                 x-dy, y+dy, dx, dy,   +3 ) );  
  104.                         }  
  105.                         // tilted haar_x4  
  106.                         if ( (x+4*dx <= winSize.width) && (y+4*dx+dy <= winSize.height) && (x-dy>= 0) )  
  107.                         {  
  108.                             features.push_back( Feature( offset, true,  
  109.                                 x,    y,    dx*4, dy, -1,  
  110.                                 x+dx, y+dx, dx*2, dy, +2 ) );  
  111.                         }  
  112.                         // tilted haar_y4  
  113.                         if ( (x+dx <= winSize.width) && (y+dx+4*dy <= winSize.height) && (x-4*dy>= 0) )  
  114.                         {  
  115.                             features.push_back( Feature( offset, true,  
  116.                                 x,    y,    dx, 4*dy, -1,  
  117.                                 x-dy, y+dy, dx, 2*dy, +2 ) );  
  118.                         }  
  119.                     }  
  120.                 }  
  121.             }  
  122.         }  
  123.     }  
  124.     numFeatures = (int)features.size();  
  125. }</span>  
接着,在 CvHaarEvaluator::Feature构造函数中,对刚刚求得的坐标做了偏移量上的转换。
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  1. <span style="font-size:14px;">CvHaarEvaluator::Feature::Feature( int offset, bool _tilted,  
  2.                                           int x0, int y0, int w0, int h0, float wt0,  
  3.                                           int x1, int y1, int w1, int h1, float wt1,  
  4.                                           int x2, int y2, int w2, int h2, float wt2 )  
  5. {  
  6.     tilted = _tilted;  
  7.   
  8.     rect[0].r.x = x0;  
  9.     rect[0].r.y = y0;  
  10.     rect[0].r.width  = w0;  
  11.     rect[0].r.height = h0;  
  12.     rect[0].weight   = wt0;  
  13.   
  14.     rect[1].r.x = x1;  
  15.     rect[1].r.y = y1;  
  16.     rect[1].r.width  = w1;  
  17.     rect[1].r.height = h1;  
  18.     rect[1].weight   = wt1;  
  19.   
  20.     rect[2].r.x = x2;  
  21.     rect[2].r.y = y2;  
  22.     rect[2].r.width  = w2;  
  23.     rect[2].r.height = h2;  
  24.     rect[2].weight   = wt2;  
  25.   
  26.     if( !tilted )  
  27.     {  
  28.         forint j = 0; j < CV_HAAR_FEATURE_MAX; j++ )  
  29.         {  
  30.             if( rect[j].weight == 0.0F )  
  31.                 break;  
  32.             CV_SUM_OFFSETS( fastRect[j].p0, fastRect[j].p1,   
  33.                             fastRect[j].p2, fastRect[j].p3, rect[j].r, offset )  
  34.         }  
  35.     }  
  36.     else  
  37.     {  
  38.         forint j = 0; j < CV_HAAR_FEATURE_MAX; j++ )  
  39.         {  
  40.             if( rect[j].weight == 0.0F )  
  41.                 break;  
  42.             CV_TILTED_OFFSETS( fastRect[j].p0, fastRect[j].p1,   
  43.                                fastRect[j].p2, fastRect[j].p3, rect[j].r, offset )  
  44.         }  
  45.     }  
  46. }  
  47. </span>  
CV_SUM_OFFSET和CV_TILTED_OFFSET是计算偏移量的宏,它们将左上角点和宽高转换成在单行sum或者tilted矩阵中的位置。sum矩阵的求法和LBP中是一样的,也是利用了OpenCV自带的cv::integral函数,而斜45度的矩阵也没有用到旋转图像之类的操作,而是…嗯,还是integral函数,自带重载功能,实现了45度倾斜操作。
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  1. <span style="font-size:14px;">void CvHaarEvaluator::setImage(const Mat& img, uchar clsLabel, int idx)  
  2. {  
  3.     CV_DbgAssert( !sum.empty() && !tilted.empty() && !normfactor.empty() );  
  4.     CvFeatureEvaluator::setImage( img, clsLabel, idx);  
  5.     Mat innSum(winSize.height + 1, winSize.width + 1, sum.type(), sum.ptr<int>((int)idx));  
  6.     Mat innTilted(winSize.height + 1, winSize.width + 1, tilted.type(), tilted.ptr<int>((int)idx));  
  7.     Mat innSqSum;  
  8.     integral(img, innSum, innSqSum, innTilted);  
  9.     normfactor.ptr<float>(0)[idx] = calcNormFactor( innSum, innSqSum );  
  10. }</span>  
归一化因子计算如下:
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  1. <span style="font-size:14px;">float calcNormFactor( const Mat& sum, const Mat& sqSum )  
  2. {  
  3.     CV_DbgAssert( sum.cols > 3 && sqSum.rows > 3 );  
  4.     Rect normrect( 1, 1, sum.cols - 3, sum.rows - 3 );  
  5.     size_t p0, p1, p2, p3;  
  6.     CV_SUM_OFFSETS( p0, p1, p2, p3, normrect, sum.step1() )  
  7.     double area = normrect.width * normrect.height;  
  8.     const int *sp = (const int*)sum.data;  
  9.     int valSum = sp[p0] - sp[p1] - sp[p2] + sp[p3];  
  10.     const double *sqp = (const double *)sqSum.data;  
  11.     double valSqSum = sqp[p0] - sqp[p1] - sqp[p2] + sqp[p3];  
  12.     return (float) sqrt( (double) (area * valSqSum - (double)valSum * valSum) );  
  13. }</span>  

SqSum是平方积分图。
最后,不同小块乘上权重系数,作为Haar特征值。
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  1. <span style="font-size:14px;">inline float CvHaarEvaluator::Feature::calc(  
  2.         const cv::Mat &_sum,  
  3.         const cv::Mat &_tilted,  
  4.         size_t y) const  
  5. {  
  6.     const int* img = tilted ?  
  7.                 _tilted.ptr<int>((int)y) : _sum.ptr<int>((int)y);  
  8.     float ret = rect[0].weight * (  
  9.                 img[fastRect[0].p0]  
  10.             - img[fastRect[0].p1]  
  11.             - img[fastRect[0].p2]  
  12.             + img[fastRect[0].p3] ) +  
  13.             rect[1].weight * (  
  14.                 img[fastRect[1].p0]  
  15.             - img[fastRect[1].p1]  
  16.             - img[fastRect[1].p2]  
  17.             + img[fastRect[1].p3] );  
  18.     if( rect[2].weight != 0.0f )  
  19.         ret += rect[2].weight * (  
  20.                     img[fastRect[2].p0]  
  21.                 - img[fastRect[2].p1]  
  22.                 - img[fastRect[2].p2]  
  23.                 + img[fastRect[2].p3] );  
  24.     return ret;  
  25. }</span>  
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