我正在尝试绘制lenna here the 8 bit single ch. gray scale image的直方图。
但它没有正确显示输出,如以下输出中所示:
void show_histogram_image(Mat img1)
{
int sbins = 256;
int histSize[] = {sbins};
float sranges[] = { 0, 256 };
const float* ranges[] = { sranges };
cv::MatND hist;
int channels[] = {0};
cv::calcHist( &img1, 1, channels, cv::Mat(), // do not use mask
hist, 1, histSize, ranges,
true, // the histogram is uniform
false );
double maxVal=0;
minMaxLoc(hist, 0, &maxVal, 0, 0);
int xscale = 10;
int yscale = 10;
cv::Mat hist_image;
hist_image = cv::Mat::zeros(256, sbins*xscale, CV_8UC1);
for( int s = 0; s < sbins; s++ )
{
float binVal = hist.at<float>(s, 0);
int intensity = cvRound(binVal*255/maxVal);
rectangle( hist_image, cv::Point(s*xscale, 0),
cv::Point( (s+1)*xscale - 1, intensity),
cv::Scalar::all(255),
CV_FILLED );
}
imshow("Image1",hist_image);
waitKey(0);
}
这是我的主要();
int main()
{
Mat img1 = imread("lena512.bmp", CV_8UC1);
if (img1.empty()) //check whether the image is valid or not
{
cout << "Error : Image cannot be read..!!" << endl;
system("pause"); //wait for a key press
return -1;
}
show_histogram_image(img1);
}
这是输出直方图图像:
我尝试更改xscale,即使它没有正确使用。
更新
我做了以下更改:
rectangle( hist_image, cv::Point(s*xscale, hist_image.rows),
cv::Point( (s+1)*xscale - 1, hist_image.rows - intensity),
cv::Scalar::all(255), CV_FILLED );
现在的输出是:
它好多了,但我需要线条和清晰可见的垃圾箱。而且看起来某些部分隐藏在右侧。
更新2
我将CV_FILLED更改为'1',现在我已经:
答案 0 :(得分:2)
因为opencv中的图像原点是(0,0),因此y轴指向下方, 你必须反转直方图绘制的y值:
rectangle( hist_image, cv::Point(s*xscale, hist_image.rows),
cv::Point( (s+1)*xscale - 1, hist_image.rows - intensity),
cv::Scalar::all(255),
CV_FILLED );