c++ - 遍历 calcHist 返回的 Mat

Question

我正在努力学习equalization of histograms , 我当然知道有 histogram equalization in OpenCV .我是iterating over the Mat object由 calcHist 返回而且我不知道这是否是正确的方法......或者还有其他方法。首先，calcHist返回一个由 float 、 double 或整数组成的垫子？我似乎无法在文档中找到它。

int histSize = 256;
float range[] = {0, 256} ;
const float* histRange = { range };

Mat histogram;
calcHist(&image, 1, 0, Mat(), histogram, 1, &histSize, &histRange);

Mat accumulatedHistogram = histogram.clone();   
MatIterator_<float> accHistIt, accHistEnd;  
accHistIt=accumulatedHistogram.begin<float>();
accHistEnd=accumulatedHistogram.end<float>();

bool firstLoop = true;

for(; accHistIt != accHistEnd; accHistIt++) {
    if(firstLoop) {                     
        firstLoop = false;
    } else {
        *accHistIt += *(accHistIt-1);
    }
}

谢谢，

Answer 1

calcHist 将返回 Mat 的 float 值。虽然类型没有很好的记录，但您可以通过查看 the documentation access its values 的方式轻松猜出它是什么。 .

如果 image 是单 channel 图像，calcHist 将计算 histSize x 1 float 矩阵，在您的示例中 histogram。请注意，histSize 通常称为 number of bins。

要迭代它的所有值，您可以这样做:

for (int i=0; i<histSize; i++)
    cout << histogram.at<float>(i, 0));

---

注意:对于像RGB这样的3 channel 图像，可以按如下方式进行:

vector<float> result;

/// Separate the image in 3 places ( B, G and R )
vector<Mat> bgr_planes;
split( image, bgr_planes );

/// Establish the number of bins
int histSize = 256;

/// Set the ranges ( for B,G,R) )
float range[] = { 0, 256 } ; //0~255 the upper boundary is exclusive
const float * histRange = { range };
bool uniform = true; 
bool accumulate = false;
Mat b_hist, g_hist, r_hist;

/// Compute the histograms:
calcHist( &bgr_planes[0], 1, 0, Mat(), b_hist, 1, &histSize, &histRange, uniform, accumulate );
calcHist( &bgr_planes[1], 1, 0, Mat(), g_hist, 1, &histSize, &histRange, uniform, accumulate );
calcHist( &bgr_planes[2], 1, 0, Mat(), r_hist, 1, &histSize, &histRange, uniform, accumulate );

/// stored in result
for (int i=0; i<histSize; i++)
    result.push_back(r_hist.at<float>(i, 0));
for (int i=0; i<histSize; i++)
    result.push_back(g_hist.at<float>(i, 0));
for (int i=0; i<histSize; i++)
    result.push_back(b_hist.at<float>(i, 0));