How to smooth a histogram?
I want to smooth a histogram.
Therefore I tried to smooth the internal matrix of cvHistogram
.
typedef struct CvHistogram
{
int type;
CvArr* bins;
float thresh[CV_MAX_DIM][2]; /* for uniform histograms */
float** thresh2; /* for non-uniform histograms */
CvMatND mat; /* embedded matrix header for array histograms */
}
I tried to开发者_Go百科 smooth the matrix like this:
cvCalcHist( planes, hist, 0, 0 ); // Compute histogram
(...)
// smooth histogram with Gaussian Filter
cvSmooth( hist->mat, hist_img, CV_GAUSSIAN, 3, 3, 0, 0 );
Unfortunately, this is not working because cvSmooth
needs a CvMat
as input instead of a CvMatND
. I couldn't transform CvMatND
into CvMat
(CvMatND
is 2-dim in my case).
Is there anybody who can help me? Thanks.
You can use the same basic algorithm used for Mean filter, just calculating the average.
for(int i = 1; i < NBins - 1; ++i)
{
hist[i] = (hist[i - 1] + hist[i] + hist[i + 1]) / 3;
}
Optionally you can use a slightly more flexible algorithm allowing you to easily change the window size.
int winSize = 5;
int winMidSize = winSize / 2;
for(int i = winMidSize; i < NBins - winMidSize; ++i)
{
float mean = 0;
for(int j = i - winMidSize; j <= (i + winMidSize); ++j)
{
mean += hist[j];
}
hist[i] = mean / winSize;
}
But bear in mind that this is just one simple technique.
If you really want to do it using OpenCv tools, I recommend you access the openCv forum: http://tech.groups.yahoo.com/group/OpenCV/join
You can dramatically change the "smoothness" of a histogram by changing the number of bins you use. A good rule of thumb is to have sqrt(n) bins if you have n data points. You might try applying this heuristic to your histogram and see if you get a better result.
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