转自：https://www.cnblogs.com/dearzhoubi/p/8621804.html

灰度直方图是灰度的函数,描述的是图像中具有该灰度级的像素的个数。如果用直角坐标系来表示,则它的横坐标是灰度级,纵坐标是该灰度出现的概率(像素的个数)。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;namespace histogram
{public partial class histForm : Form{//利用构造函数实现窗体之间的数据传递public histForm(Bitmap bmp){InitializeComponent();//把主窗体的图像数据传递给从窗体bmpHist = bmp;//灰度级计数countPixel = new int[256];  //8位可表示256个灰度级}private void close_Click(object sender, EventArgs e){this.Close();}//图像数据private System.Drawing.Bitmap bmpHist;//灰度等级private int[] countPixel;//记录最大的灰度级个数private int maxPixel;/// <summary>/// 计算各个灰度级所具有的像素个数/// </summary>private void histForm_Load(object sender, EventArgs e){//锁定8位灰度位图Rectangle rect = new Rectangle(0, 0, bmpHist.Width, bmpHist.Height);System.Drawing.Imaging.BitmapData bmpData = bmpHist.LockBits(rect,System.Drawing.Imaging.ImageLockMode.ReadWrite, bmpHist.PixelFormat);IntPtr ptr = bmpData.Scan0;int bytes = bmpHist.Width * bmpHist.Height;byte[] grayValues = new byte[bytes];System.Runtime.InteropServices.Marshal.Copy(ptr, grayValues, 0, bytes);//灰度值数据存入grayValues中byte temp = 0;maxPixel = 0;//灰度等级数组清零Array.Clear(countPixel, 0, 256);//计算各个灰度级的像素个数for (int i = 0; i < bytes; i++){//灰度级temp = grayValues[i];//计数加1countPixel[temp]++;if (countPixel[temp] > maxPixel){//找到灰度频率最大的像素数，用于绘制直方图maxPixel = countPixel[temp];}}//解锁System.Runtime.InteropServices.Marshal.Copy(grayValues, 0, ptr, bytes);bmpHist.UnlockBits(bmpData);}/// <summary>/// 绘制直方图/// </summary>private void histForm_Paint(object sender, PaintEventArgs e){//获取Graphics对象Graphics g = e.Graphics;//创建一个宽度为1的黑色钢笔Pen curPen = new Pen(Brushes.Black, 1);//绘制坐标轴g.DrawLine(curPen, 50, 240, 320, 240);//横坐标g.DrawLine(curPen, 50, 240, 50, 30);//纵坐标//绘制并标识坐标刻度g.DrawLine(curPen, 100, 240, 100, 242);g.DrawLine(curPen, 150, 240, 150, 242);g.DrawLine(curPen, 200, 240, 200, 242);g.DrawLine(curPen, 250, 240, 250, 242);g.DrawLine(curPen, 300, 240, 300, 242);g.DrawString("0", new Font("New Timer", 8), Brushes.Black, new PointF(46, 242));g.DrawString("50", new Font("New Timer", 8), Brushes.Black, new PointF(92,242));g.DrawString("100", new Font("New Timer", 8), Brushes.Black, new PointF(139, 242));g.DrawString("150", new Font("New Timer", 8), Brushes.Black, new PointF(189, 242));g.DrawString("200", new Font("New Timer", 8), Brushes.Black, new PointF(239, 242));g.DrawString("250", new Font("New Timer", 8), Brushes.Black, new PointF(289, 242));g.DrawLine(curPen, 48, 40, 50, 40);g.DrawString("0", new Font("New Timer", 8), Brushes.Black, new PointF(34, 234));g.DrawString(maxPixel.ToString(), new Font("New Timer", 8), Brushes.Black, new PointF(18, 34));//绘制直方图double temp = 0;for (int i = 0; i < 256; i++){//纵坐标长度temp = 200.0 * countPixel[i] / maxPixel;g.DrawLine(curPen, 50 + i, 240, 50 + i, 240 - (int)temp);}//释放对象curPen.Dispose();}}
}