c++ - Trying to compute my own Histogram without opencv calcHist() -

what i'm trying writing function calculates histogram of greyscale image forwarded number of bins (anzbin) histograms range divided in. i'm running through image pixels compairing value different bins , in case value fits, increasing value of bin 1

   vector<int> calcuhisto(const iplimage *src_pic, int anzbin)     {    cvsize size = cvgetsize(src_pic);    int binsize = (size.width / 256)*anzbin;    vector<int> histogram(anzbin,0);      (int y = 0; y<size.height; y++)      {          const uchar *src_pic_point =         (uchar *)(src_pic->imagedata + y*src_pic->widthstep);        (int x = 0; x<size.width; x++)         {         (int z = 0; z < anzbin; z++)         {             if (src_pic_point[x] <= z*binsize)             {                 histogram[src_pic_point[x]]++;             }          }      } } return histogram; } 

but unfortunately it's not working... wrong here? please help

there few issues can see

1. your binsize calculation wrong
2. your binning algorithm 1 sided, , should 2 sided
3. you aren't incrementing proper bin when find match

1. binsize calculation

bin size = range / number of bins

2. 2 sided binning

if (src_pic_point[x] <= z*binsize) 

you need 2 sided range of values, not 1 sided inequality. imagine have 4 bins , values 0 255. bins should have following ranges

bin     low     high 0       0       63.75 1       63.75   127.5 2       127.5   191.25 3       191.25  255 

for example: value of 57 should go in bin 0. code says value goes in bins! because <= z*binsize need something lower , upper bound.

3. incrementing appropriate bin

you using z loop on each bin, when find match should increment bin z, don't use actual pixel value except when determining bin belongs to

this buffer overrun imagine again have 4 bins, , current pixel has value of 57. code says increment bin 57. have 4 bins (0-3)

histogram[src_pic_point[x]]++; 

you want increment bin pixel value falls

histogram[z]++; 

code
in mind here revised code (it untested, should work)

vector<int> calcuhisto(const iplimage *src_pic, int anzbin)  {     cvsize size = cvgetsize(src_pic);     double binsize = 256.0 / anzbin;        //new definition     vector<int> histogram(anzbin,0);        //i don't know if works                                             //so leave      //goes through rows     (int y = 0; y<size.height; y++)      {         //grabs entire row of imagedata         const uchar *src_pic_point = (uchar *)(src_pic->imagedata + y*src_pic->widthstep);          //goes through each column         (int x = 0; x<size.width; x++)          {             //for each bin             (int z = 0; z < anzbin; z++)             {                 //check both upper , lower limits                 if (src_pic_point[x] >= z*binsize && src_pic_point[x] < (z+1)*binsize)                 {                     //increment index contains point                     histogram[z]++;                 }             }         }     }     return histogram; }