opencv2+ Introduction Series (iv): Calculate the histogram of the image, average grayscale, gray variance

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In the image processing, we often need to find out the histogram of the image, gray average, gray variance, here is a opencv2+ to bring a program to achieve these functions.

Histogram

For histograms, use the Cv::calchist function to find out.

Prototype

void Calchist (const mat* arrays, int narrays, const int* channels, Inputarray mask, Outputarray
hist, int dims, const int* histsize, const float** ranges, BOOL uniform=true, BOOL accumulate=
false); void Calchist (const mat* arrays, int narrays, const int* channels, Inputarray mask, sparsemat&
hist, int dims, const int* histsize, const float** ranges, BOOL uniform=true, BOOL accumulate=
FALSE);

• Arrays: Input image (or array, array set)
• Narrays: Number of input arrays
• Channels: The channel to be counted
• Mask: Mask (0 means ignore this pixel), if undefined, no mask is used
• hist: Matrix for storing histograms
• Dims: Dimension of histogram
• histsize: Number of bins per dimension
• Ranges: the range of values for each dimension
• uniform and accumulate: Bin size Same, clear histogram traces

Here's a way to calculate the histogram I've encapsulated.

1 voidGetgrayhist (cv::mat& src, cv::mat& grayhist,intHistsize=255)2 {3     floatRange[] = {0,255 };4     Const float* Histrange ={range};5     BOOLUniform =true;BOOLaccumulate =false;6(&SRC,1,0, Cv::mat (), Grayhist,1, &histsize, &histrange, uniform, accumulate);7}

Mean and variance

Calculation of mean and variance using Cv::meanstddev function

The function has four input parameters

1Mat Images

2Mat average, calculated to become Float64 type (double) 1*1.

3Mat Variance, the calculation will also become Float64 type 1*1.

4 Masking film

Here is a program that calculates the average grayscale and gray variance of an image:

voidGetgrayavgstddev (cv::mat& src,Double& AVG,Double&StdDev)    {Cv::mat img; if(Src.channels () = =3) cv::cvtcolor (SRC, img, cv_bgr2gray); Elseimg=src;    Cv::mean (SRC);    Cv::mat mean;    Cv::mat StdDev;    Cv::meanstddev (IMG, mean, StdDev); Avg= mean.ptr<Double> (0)[0]; StdDev= stddev.ptr<Double> (0)[0];}

opencv2+ Introduction Series (iv): Calculate the histogram of the image, average grayscale, gray variance