C#绘制数字图像灰度直方图

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）。

灰度直方图的分布函数：

其中，K是指第k个灰度级，如果是8位灰度图像，k=0、1、……、255。

处理图像生成直方图数据

//将图像数据复制到byte中
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 * 3;
byte[] grayValues = new byte[bytes];
System.Runtime.InteropServices.Marshal.Copy(ptr, grayValues, 0, bytes);
 
//统计直方图信息
byte temp = 0;
maxPixel = 0;
Array.Clear(countPixel, 0, 256);
for (int i = 0; i < bytes; i++)
{
    temp = grayValues[i];
    countPixel[temp]++;
    if (countPixel[temp] > maxPixel)
    {
        maxPixel = countPixel[temp];
    }
}
 
System.Runtime.InteropServices.Marshal.Copy(grayValues, 0, ptr, bytes);
bmpHist.UnlockBits(bmpdata);

绘制直方图信息

//画出坐标系
Graphics g = e.Graphics;
Pen curPen = new Pen(Brushes.Black, 1);
 
g.DrawLine(curPen, 50, 240, 320, 240);
g.DrawLine(curPen, 50, 240, 50, 30);
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));
 
double temp = 0;
for (int i = 0; i < 256; i++)
{
    temp = 200.0 * countPixel[i] / maxPixel;
    g.DrawLine(curPen, 50 + i, 240, 50 + i, 240 - (int)temp);
}
 
curPen.Dispose();

全局变量定义及赋值

private System.Drawing.Bitmap bmpHist;
private int[] countPixel;
private int maxPixel;
 
public Grey_ScaleMapForm(Bitmap bmp)
{
    InitializeComponent();
    bmpHist = bmp;
    countPixel = new int[256];
}