灰度直方图

cv::Mat opencvTool::calculateHistogram(const cv::Mat& image)
{
	// 如果输入图像尚未处于灰度级，请将其转换为灰度级
	cv::Mat grayscale_image;
	if (image.channels() > 1)
	{
		cv::cvtColor(image, grayscale_image, cv::COLOR_BGR2GRAY);
	}
	else
	{
		grayscale_image = image.clone();
	}

	// 计算直方图
	cv::Mat hist;
	int histSize = 256;
	float range[] = { 0, 256 };
	const float* histRange = { range };
	bool uniform = true, accumulate = false;
	cv::calcHist(&grayscale_image, 1, nullptr, cv::Mat(), hist, 1, &histSize, &histRange, uniform, accumulate);

	// 绘制直方图
	int hist_w = 512, hist_h = 400;
	int bin_w = cvRound((double)hist_w / histSize);
	cv::Mat histImage(hist_h, hist_w, CV_8UC3, cv::Scalar(255, 255, 255));
	cv::normalize(hist, hist, 0, histImage.rows, cv::NORM_MINMAX, -1, cv::Mat());

	for (int i = 1; i < histSize; i++)
	{
		cv::line(histImage, cv::Point(bin_w * (i - 1), hist_h - cvRound(hist.at<float>(i - 1))),
			cv::Point(bin_w * (i), hist_h - cvRound(hist.at<float>(i))),
			cv::Scalar(0, 0, 0), 2, 8, 0);
	}

	return histImage;
}