OpenCV學習——繪製圖像灰色直方圖

一、環境

OpenCV3.4.1

VS2015

二、代碼

#include <opencv2/opencv.hpp>
using namespace std;
#pragma comment(linker, "/subsystem:\"windows\" /entry:\"mainCRTStartup\"")
#define cvQueryHistValue_1D( hist, idx0 )  ((float)cvGetReal1D( (hist)->bins, (idx0)))
void FillWhite(IplImage *pImage)
{
	cvRectangle(pImage, cvPoint(0, 0), cvPoint(pImage->width, pImage->height), CV_RGB(255, 255, 255), CV_FILLED);
}
// 創建灰度圖像的直方圖
CvHistogram* CreateGrayImageHist(IplImage **ppImage)
{
	int nHistSize = 256;
	float fRange[] = { 0, 255 };  //灰度級的範圍  
	float *pfRanges[] = { fRange };
	CvHistogram *pcvHistogram = cvCreateHist(1, &nHistSize, CV_HIST_ARRAY, pfRanges);
	cvCalcHist(ppImage, pcvHistogram);
	return pcvHistogram;
}
// 根據直方圖創建直方圖圖像
IplImage* CreateHisogramImage(int nImageWidth, int nScale, int nImageHeight, CvHistogram *pcvHistogram)
{
	IplImage *pHistImage = cvCreateImage(cvSize(nImageWidth * nScale, nImageHeight), IPL_DEPTH_8U, 1);
	FillWhite(pHistImage);

	//統計直方圖中的最大直方塊
	float fMaxHistValue = 0;
	cvGetMinMaxHistValue(pcvHistogram, NULL, &fMaxHistValue, NULL, NULL);

	//分別將每個直方塊的值繪製到圖中
	int i;
	for (i = 0; i < nImageWidth; i++)
	{
		float fHistValue = cvQueryHistValue_1D(pcvHistogram, i); //像素爲i的直方塊大小
		int nRealHeight = cvRound((fHistValue / fMaxHistValue) * nImageHeight);  //要繪製的高度
		cvRectangle(pHistImage,
			cvPoint(i * nScale, nImageHeight - 1),
			cvPoint((i + 1) * nScale - 1, nImageHeight - nRealHeight),
			cvScalar(i, 0, 0, 0),
			CV_FILLED
		);
	}
	return pHistImage;
}
int main(int argc, char** argv)
{
	const char *pstrWindowsSrcTitle = "原圖(https://blog.csdn.net/Aidam_Bo)";
	const char *pstrWindowsGrayTitle = "灰度圖(https://blog.csdn.net/Aidam_Bo)";
	const char *pstrWindowsHistTitle = "直方圖(https://blog.csdn.net/Aidam_Bo)";

	// 從文件中加載原圖
	IplImage *pSrcImage = cvLoadImage("test.jpg", CV_LOAD_IMAGE_UNCHANGED);
	IplImage *pGrayImage = cvCreateImage(cvGetSize(pSrcImage), IPL_DEPTH_8U, 1);
	// 灰度圖
	cvCvtColor(pSrcImage, pGrayImage, CV_BGR2GRAY);

	// 灰度直方圖
	CvHistogram *pcvHistogram = CreateGrayImageHist(&pGrayImage);

	// 創建直方圖圖像
	int nHistImageWidth = 255;
	int nHistImageHeight = 150;  //直方圖圖像高度
	int nScale = 2;
	IplImage *pHistImage = CreateHisogramImage(nHistImageWidth, nScale, nHistImageHeight, pcvHistogram);

	// 顯示
	cvNamedWindow(pstrWindowsSrcTitle, CV_WINDOW_AUTOSIZE);
	cvNamedWindow(pstrWindowsGrayTitle, CV_WINDOW_AUTOSIZE);
	cvNamedWindow(pstrWindowsHistTitle, CV_WINDOW_AUTOSIZE);
	cvShowImage(pstrWindowsSrcTitle, pSrcImage);
	cvShowImage(pstrWindowsGrayTitle, pGrayImage);
	cvShowImage(pstrWindowsHistTitle, pHistImage);


	cvWaitKey(0);

	cvReleaseHist(&pcvHistogram);

	cvDestroyWindow(pstrWindowsSrcTitle);
	cvDestroyWindow(pstrWindowsGrayTitle);
	cvDestroyWindow(pstrWindowsHistTitle);
	cvReleaseImage(&pSrcImage);
	cvReleaseImage(&pGrayImage);
	cvReleaseImage(&pHistImage);
	return 0;
}

注意：這裏用到函數 cvQueryHistValue_1D是OpenCV2的，在OpenCV3中沒有這個函數，筆者使用的OpenCV是3.4.1版本，所以定義宏來使用cvQueryHistValue_1D：

#define cvQueryHistValue_1D( hist, idx0 )  ((float)cvGetReal1D( (hist)->bins, (idx0)))

 

 

三、結果展示

灰色直方圖