c# - How to detect black Bullets in Image? -

given following image, how can detect black bullets (90 bullet) in image using c#, emgucv or aforge?

i tried use getpixel(x,y) method checks pixel pixel, slow , need detect bullets not pixels.

algorithm/idea 1 can divide image in squares shown in sample:

with logic have check every 20th pixel. know first dot is, know every other dot have in same horizontal line (in provided sample).

a sample algorithm similar (please note need further improvement):

bitmap mybitmap = new bitmap ("input.png");  int skipx = 12; int skipy = 12;  int detecteddots = 0;  (int x = 0; x < mybitmap.width; x += skipx) {     (int y = 0; y < mybitmap.height; y += skipy) {         color pixelcolor = mybitmap.getpixel (x, y);          if (pixelcolor.r + pixelcolor.g + pixelcolor.b == 0) {             mybitmap.setpixel (x, y, color.red);             detecteddots++;         }     } }  mybitmap.save ("output.png");  console.writeline (detecteddots + " dots detected"); 

i added output can check dots got detected (all containing red pixels).

further improvement find center of dot. after should know width (and height) , can start @ first upper left dot offset of dots width.

algorithm 2 second algorithm analyses each pixel , lot easier implement. there's black pixel checks if there black pixel in same vertical or horizontal line before , skips in case until there no black pixel in line.

further improvement store height of first dot , make condition in middle of snippet more beautiful.

stopwatch watch = new stopwatch(); watch.start();  bitmap mybitmap = new bitmap ("input.png");  int dotsdetected = 0;   list<int> xfound = new list<int>();   (int x = 0; x < mybitmap.width; x++) {     bool yfound = false;     bool dotfound = false;     (int y = 0; y < mybitmap.height; y++) {         color pixelcolor = mybitmap.getpixel (x, y);         if (pixelcolor.r + pixelcolor.g + pixelcolor.b == 0) {             dotfound = true;              if (yfound)                 continue;              if (xfound.contains (y)                  || xfound.contains (y + 1)                  || xfound.contains (y + 2)                  || xfound.contains (y + 3)                 || xfound.contains (y + 4)                 || xfound.contains (y - 1)                  || xfound.contains (y - 2)                  || xfound.contains (y - 3)                 || xfound.contains (y - 4)) {                 yfound = true;                 continue;             }              xfound.add (y);             //mybitmap.setpixel (x, y, color.red);              dotsdetected++;             yfound = true;         } else             yfound = false;     }      if(!dotfound) //no dot found in line         xfound.clear(); }  //mybitmap.save ("output.png");  watch.stop();  console.writeline("picture analyzed in " + watch.elapsed.totalseconds.tostring("#,##0.0000"));  console.writeline (dotsdetected + " dots detected");