尝试不使用opencv calcHist（）来计算自己的直方图

Question

What I'm trying to do is writing a function that calculates a Histogram of a greyscale image with a forwarded Number of Bins (anzBin) which the histograms range is divided in. Then I'm running through the Image Pixels compairing their value to the different Bins and in case a value fits, increasing the value of the Bin by 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);

    for (int y = 0; y<size.height; y++) 
    {
         const uchar *src_pic_point =
        (uchar *)(src_pic->imageData + y*src_pic->widthStep);
       for (int x = 0; x<size.width; x++) 
       {
        for (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... What is wrong here? Please help

Answer 1

There are a few issues I can see

1. Your binSize calculation is wrong
2. Your binning algorithm is one sided, and should be two sided
3. You aren't incrementing the proper bin when you find a match

1. binsize calculation

bin size = your range / number of bins

2. two sided binning

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

you need a two sided range of values, not a one sided inequality. Imagine you have 4 bins and values from 0 to 255. Your bins should have the 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: a value of 57 should go in bin 0. Your code says the value goes in all the bins! Because its always <= z*binsize You need something something with a lower and upper bound.

3. Incrementing the appropriate bin

You are using z to loop over each bin, so when you find a match you should increment bin z , you don't use the actual pixel value except when determining which bin it belongs to

this would likely be buffer overrun imagine again you have 4 bins, and the current pixel has a value of 57. This code says increment bin 57. But you only have 4 bins (0-3)

histogram[src_pic_point[x]]++;

you want to increment only the bin the pixel value falls into

histogram[z]++;

CODE
With that in mind here is revised code (it is untested, but 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 this works so I
                                            //so I will leave it

    //goes through all rows
    for (int y = 0; y<size.height; y++) 
    {
        //grabs an entire row of the imageData
        const uchar *src_pic_point = (uchar *)(src_pic->imageData + y*src_pic->widthStep);

        //goes through each column
        for (int x = 0; x<size.width; x++) 
        {
            //for each bin
            for (int z = 0; z < anzBin; z++)
            {
                //check both upper and lower limits
                if (src_pic_point[x] >= z*binSize && src_pic_point[x] < (z+1)*binSize)
                {
                    //increment the index that contains the point
                    histogram[z]++;
                }
            }
        }
    }
    return histogram;
}