Color histogram of image features

Color space of OpenCV:

Color space RGB (red red, green Green, blue blue)

Value range of R: 0-255

Value range of G: 0-255

Value range of B: 0-255

Color space HSV (hue hue, saturation saturation, intensity brightness)

Value range of H: 0-179

Value range of S: 0-255

Value range of V: 0-255

Color Space HLs (hue hue, lightness brightness, saturation saturation)

Value range of H: 0-179

L range of values: 0-255

Value range of S: 0-255

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Knowing the range of pixels used in the various channels of the color space, we discuss the color histogram below

One-dimensional histogram:

For example, we only calculate the histogram of the S channel and have 30 bins.

<span Style= "FONT-SIZE:18PX;" > #include <opencv2\core\core.hpp> #include <opencv2\highgui\highgui.hpp> #include <opencv2\ Imgproc\imgproc.hpp>using namespace CV; #include <iostream>using namespace Std;int main (int argc, char** argv) { Mat src,hsv;if (argc! = 2 | |! ( src = imread (argv[1],1)). Data | | Src.channels ()! = 3) return-1;//Conversion of color space BGR to Hsvcvtcolor (SRC,HSV,CV_BGR2HSV);//divide H channel into 30 bin, divide s channel into 32binint hbins = 30 //int sbins = 32;//int histsize[] = {Hbins,sbins};int histsize[] = {hbins};//h value range 0-179float Hranges [] = {0,180};//s fetch Value range 0-255//float Sranges [] ={0,255};//const float* ranges [] = {hranges,sranges};const float* ranges [] = {hranges}; Matnd hist;//We are based on the image of the first Channel one-dimensional histogram int channels[] = {0};calchist (&hsv,1,channels,mat (), Hist,1,histsize,ranges,true, FALSE);//output histogram Cout<

Output, a 30-dimensional vector is definitely:

Explanation: The first number 60571is the number of pixels that represent h between [0,5] , and the second number 12194 is the number of pixels that represent h in the [6,11] point.
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Two-dimensional histogram:
<span style= "FONT-SIZE:18PX;" ><span style= "Font-family:microsoft yahei;font-size:14px;" ><span style= "Font-family:microsoft yahei;font-size:14px;" > #include <opencv2\core\core.hpp> #include <opencv2\highgui\highgui.hpp> #include <opencv2\ Imgproc\imgproc.hpp>using namespace CV; #include <iostream>using namespace Std;int main (int argc, char** argv) { Mat src,hsv;if (argc! = 2 | |! ( src = imread (argv[1],1)). Data | | Src.channels ()! = 3) return-1;//The conversion of the color space BGR to Hsvcvtcolor (SRC,HSV,CV_BGR2HSV);//The H channel is divided into 30 bins, the S channel is divided into 32binint hbins = 5; int sbins = 4;int histsize[] = {hbins,sbins};//h value range 0-179float Hranges [] = {0,180};//s value range 0-255float sranges [] ={0,2 56};const float* Ranges [] = {hranges,sranges}; Matnd hist;//We calculate the two-dimensional histogram int channels[] = {0,1};calchist (&hsv,1,channels,mat (), Hist,2,histsize, for the first and second channels of the image, Ranges,true,false);//output histogram Cout<

In our case, the output of the two-dimensional histogram is:

Now let's explain that this is a 5 row 4 column Two-dimensional histogram, the first row of the first column of the 128239, representing the values of H and S in [0,35]x[0,63], the second row in the first column of 18585 the values for H and S are in [36,71]x[0,63], and so on, how to verify? We just need to change the above procedure to a few numbers, for example we only calculate the histogram of H and S values in [36,71]x[0,63]  :
<span style= "FONT-SIZE:18PX;" > #include <opencv2\core\core.hpp> #include <opencv2\highgui\highgui.hpp> #include <opencv2\ Imgproc\imgproc.hpp>using namespace CV; #include <iostream>using namespace Std;int main (int argc, char** argv) { Mat src,hsv;if (argc! = 2 | |! ( src = imread (argv[1],1)). Data | | Src.channels ()! = 3) return-1;//The conversion of the color space BGR to Hsvcvtcolor (SRC,HSV,CV_BGR2HSV);//Divide the H-Channel into 30 bins and divide the S-channel into 32binint hbins  = 1;int Sbins = 1;int histsize[] = {hbins,sbins};//h value range 0-179float Hranges [] = {36,72};//s range 0-255float sranges [] ={0,64};const float* ranges [] = {hranges,sranges}; Matnd hist;//We calculate the two-dimensional histogram int channels[] = {0,1};calchist (&hsv,1,channels,mat (), Hist,2,histsize, for the first and second channels of the image, Ranges,true,false);//output histogram Cout<

Output Result:
。
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Understand the simple color histogram, the color histogram as a simple feature of the picture, do a simple image retrieval.
Color histogram of image features