c#图像处理入门的一个好方法-bitmap类和图像像素值获取方法
一．Bitmap类
Bitmap对象封装了ＧＤＩ+中的一个位图，此位图由图形图像及其属性的像素数据组成.因此Bitmap是用于处理由像素数据定义的图像的对象.该类的主要方法和属性如下：
- 1. GetPixel方法和 SetPixel方法：获取和设置一个图像的指定像素的颜色.
- 2. PixelFormat属性：返回图像的像素格式.
- 3. Palette属性：获取和设置图像所使用的颜色调色板.
- 4. Height Width属性：返回图像的高度和宽度.
- 5. LockBits 方法和UnlockBits方法：分别锁定和解锁系统内存中的位图像素.在基于像素点的图像处理方法中使用LockBits 和UnlockBits是一个很好的方式，这两种方法可以使我们指定像素的范围来控制位图的任意一部分，从而消除了通过循环对位图的像素逐个进行处理，每调用LockBits 之后都应该调用一次UnlockBits.
二．BitmapData类
BitmapData对象指定了位图的属性
- 1. Height属性：被锁定位图的高度.
- 2. Width属性：被锁定位图的高度.
- 3. PixelFormat属性：数据的实际像素格式.
- 4. Scan0属性：被锁定数组的首字节地址，如果整个图像被锁定，则是图像的第一个字节地址.
- 5. Stride属性：步幅，也称为扫描宽度.
如上图所示,数组的长度并不一定等于图像像素数组的长度,还有一部分未用区域,这涉及到位图的数据结构,系统要保证每行的字节数必须为4的倍数.
三．Graphics类
Graphics对象是ＧＤＩ+的关键所在，许多对象都是由Graphics类表示的，该类定义了绘制和填充图形对象的方法和属性，一个应用程序只要需要进行绘制或着色，它就必须使用Graphics对象.
四．Image类
这个类提供了位图和元文件操作的函数.Image类被声明为abstract,也就是说Image类不能实例化对象,而只能做为一个基类.
1.FromFile方法：它根据输入的文件名产生一个Image对象,它有两种函数形式:
public static Image FromFile(string filename);
public static Image FromFile(string filename, bool useEmbeddedColorManagement);
2.FromHBitmap方法：它从一个windows句柄处创建一个bitmap对象, 它也包括两种函数形式:
public static bitmap fromhbitmap(intptr hbitmap);
public static bitmap fromhbitmap(intptr hbitmap, intptr hpalette);
3. FromStream方法：从一个数据流中创建一个image对象,它包含三种函数形式 :
public static image fromstream(stream stream);
public static image fromstream(stream stream, bool useembeddedcolormanagement);
fromstream(stream stream, bool useembeddedcolormanagement, bool validateimagedata);
有了上面的了解，我们便可以开始利用Ｃ#做图像处理，下面介绍几种方法：
一. 打开、保存、显示图像
private Bitmap srcBitmap = null;
private Bitmap showBitmap = null;
//打开文件
private void menuFileOpen_Click(object sender, EventArgs e)
{
OpenFileDialog openFileDialog = new OpenFileDialog();
openFileDialog.Filter = @"Bitmap文件(*.bmp)|*.bmp|Jpeg文件(*.jpg)|*.jpg|所有合适文件(*.bmp,*.jpg)|*.bmp;*.jpg";
openFileDialog.FilterIndex = 3;
openFileDialog.RestoreDirectory = true;
if (DialogResult.OK == openFileDialog.ShowDialog())
{
srcBitmap = (Bitmap)Bitmap.FromFile(openFileDialog.FileName, false);
showBitmap = srcBitmap;
this.AutoScroll = true;
this.AutoScrollMinSize = new Size((int)(showBitmap.Width), (int)(showBitmap.Height));
this.Invalidate();
}
}
//保存图像文件
private void menuFileSave_Click(object sender, EventArgs e)
{
if (showBitmap != null)
{
SaveFileDialog saveFileDialog = new SaveFileDialog();
saveFileDialog.Filter = @"Bitmap文件(*.bmp)|*.bmp|Jpeg文件(*.jpg)|*.jpg|所有合适文件(*.bmp,*.jpg)|*.bmp;*.jpg";
saveFileDialog.FilterIndex = 3;
saveFileDialog.RestoreDirectory = true;
if (DialogResult.OK == saveFileDialog.ShowDialog())
{
ImageFormat format = ImageFormat.Jpeg;
switch (Path.GetExtension(saveFileDialog.FileName).ToLower())
{
case ".jpg":
format = ImageFormat.Jpeg;
break;
case ".bmp":
format = ImageFormat.Bmp;
break;
default:
MessageBox.Show(this, "Unsupported image format was specified", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error);
return;
}
try
{
showBitmap.Save(saveFileDialog.FileName,format );
}
catch (Exception)
{
MessageBox.Show(this, "Failed writing image file", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error);
}
}
}
}
//窗口重绘,在窗体上显示图像,重载Paint
private void frmMain_Paint(object sender, System.Windows.Forms.PaintEventArgs e)
{
if (showBitmap != null)
{
Graphics g = e.Graphics;
g.DrawImage(showBitmap, new Rectangle(this.AutoScrollPosition.X, this.AutoScrollPosition.Y ,
(int)(showBitmap.Width), (int)(showBitmap.Height)));
}
}
//灰度化
private void menu2Gray_Click(object sender, EventArgs e)
{
if (showBitmap == null) return;
showBitmap = RGB2Gray(showBitmap);//下面都以RGB2Gray为例
this.Invalidate();
}
二. 提取像素法
这种方法简单易懂,但相当耗时,完全不可取.
public static Bitmap RGB2Gray(Bitmap srcBitmap)
{
Color srcColor;
int wide = srcBitmap.Width;
int height = srcBitmap.Height;
for (int y = 0; y < height; y++)
for (int x = 0; x < wide; x++)
{
//获取像素的ＲＧＢ颜色值
srcColor = srcBitmap.GetPixel(x, y);
byte temp = (byte)(srcColor.R * .299 + srcColor.G * .587 + srcColor.B * .114);
//设置像素的ＲＧＢ颜色值
srcBitmap.SetPixel(x, y, Color.FromArgb(temp, temp, temp));
}
return srcBitmap ;
}//#
三. 内存法
这是比较常用的方法
public static Bitmap RGB2Gray(Bitmap srcBitmap)
{
int wide = srcBitmap.Width;
int height = srcBitmap.Height;
Rectangle rect = new Rectangle(0, 0, wide, height);
// 将Bitmap锁定到系统内存中, 获得BitmapData
BitmapData srcBmData = srcBitmap.LockBits(rect,
ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
//创建Bitmap
Bitmap dstBitmap = CreateGrayscaleImage(wide, height);//这个函数在后面有定义
BitmapData dstBmData = dstBitmap.LockBits(rect,
ImageLockMode.ReadWrite, PixelFormat.Format8bppIndexed);
// 位图中第一个像素数据的地址。它也可以看成是位图中的第一个扫描行
System.IntPtr srcPtr = srcBmData.Scan0;
System.IntPtr dstPtr = dstBmData.Scan0;
// 将Bitmap对象的信息存放到byte数组中
int src_bytes = srcBmData.Stride * height;
byte[] srcValues = new byte[src_bytes];
int dst_bytes = dstBmData.Stride * height;
byte[] dstValues = new byte[dst_bytes];
//复制GRB信息到byte数组
System.Runtime.InteropServices.Marshal.Copy(srcPtr, srcValues, 0, src_bytes);
System.Runtime.InteropServices.Marshal.Copy(dstPtr, dstValues, 0, dst_bytes);
// 根据Y=0.299*R+0.114*G+0.587B,Y为亮度
for (int i = 0; i < height; i++)
for (int j = 0; j < wide; j++)
{
//只处理每行中图像像素数据,舍弃未用空间
//注意位图结构中RGB按BGR的顺序存储
int k = 3 * j;
byte temp = (byte)(srcValues[i * srcBmData.Stride + k + 2] * .299
+ srcValues[i * srcBmData.Stride + k + 1] * .587 + srcValues[i * srcBmData.Stride + k] * .114);
dstValues[i * dstBmData.Stride + j] = temp;
}
//将更改过的byte[]拷贝到原位图
System.Runtime.InteropServices.Marshal.Copy(dstValues, 0, dstPtr, dst_bytes);
// 解锁位图
srcBitmap.UnlockBits(srcBmData);
dstBitmap.UnlockBits(dstBmData);
return dstBitmap;
}//#
四 指针法
C/C++的习惯,不是C#的特点
public static Bitmap RGB2Gray(Bitmap srcBitmap)
{
int wide = srcBitmap.Width;
int height = srcBitmap.Height ;
Rectangle rect = new Rectangle(0, 0, wide, height);
BitmapData srcBmData = srcBitmap.LockBits(rect,
ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
Bitmap dstBitmap = CreateGrayscaleImage(wide, height);
BitmapData dstBmData = dstBitmap.LockBits(rect,
ImageLockMode.ReadWrite, PixelFormat.Format8bppIndexed);
System.IntPtr srcScan = srcBmData.Scan0;
System.IntPtr dstScan = dstBmData.Scan0;
Unsafe //启动不安全代码
{
byte* srcP = (byte*)(void*) srcScan;
byte* dstP = (byte*)(void*) dstScan;
int srcOffset = srcBmData.Stride - wide * 3;
int dstOffset = dstBmData.Stride - wide ;
byte red, green, blue;
for (int y = 0; y < height; y++)
{
for (int x = 0; x <wide ; x++, srcP += 3, dstP++)
{
blue = srcP [0];
green = srcP [1];
red = srcP [2];
* dstP = (byte)(.299 * red + .587 * green + .114 * blue);
}
srcP += srcOffset;
dstP += dstOffset;
}
}
srcBitmap.UnlockBits(srcBmData);
dstBitmap.UnlockBits(dstBmData );
return dstBitmap;
}//#
五. 矩阵法
并不是什么新方法,只是将图像数据分做R,G,B三个矩阵(二维数组)存储,类似MATLAB的习惯.
public static bool GetRGB(Bitmap Source, out int[,] R, out int[,] G, out int[,] B)
{
try
{
int iWidth = Source.Width;
int iHeight = Source.Height;
Rectangle rect = new Rectangle(0, 0, iWidth, iHeight);
System.Drawing.Imaging.BitmapData bmpData = Source.LockBits(rect, System.Drawing.Imaging.ImageLockMode.ReadWrite, Source.PixelFormat);
IntPtr iPtr = bmpData.Scan0;
int iBytes = iWidth * iHeight * 3;
byte[] PixelValues = new byte[iBytes];
System.Runtime.InteropServices.Marshal.Copy(iPtr, PixelValues, 0, iBytes);
Source.UnlockBits(bmpData);
// 注意这个地方图像的两维方向与数组两维的方向是转置的关系
R = new int[iHeight, iWidth];
G = new int[iHeight, iWidth];
B = new int[iHeight, iWidth];
int iPoint = 0;
for (int i = 0; i < iHeight; i++)
{
for (int j = 0; j < iWidth; j++)
{
// 注意，Windows 中三基色的排列顺序是 BGR 而不是 RGB！
B[i, j] = Convert.ToInt32(PixelValues[iPoint++]);
G[i, j] = Convert.ToInt32(PixelValues[iPoint++]);
R[i, j] = Convert.ToInt32(PixelValues[iPoint++]);
}
}
return true;
}
catch (Exception)
{
R = null;
G = null;
B = null;
return false;
}
}//#
public static Bitmap FromRGB(int[,] R, int[,] G, int[,] B)
{
int iWidth = G.GetLength(1);
int iHeight = G.GetLength(0);
Bitmap Result = new Bitmap(iWidth, iHeight, System.Drawing.Imaging.PixelFormat.Format24bppRgb);
Rectangle rect = new Rectangle(0, 0, iWidth, iHeight);
System.Drawing.Imaging.BitmapData bmpData = Result.LockBits(rect, System.Drawing.Imaging.ImageLockMode.ReadWrite, System.Drawing.Imaging.PixelFormat.Format24bppRgb);
IntPtr iPtr = bmpData.Scan0;
int iStride = bmpData.Stride;
int iBytes = iWidth * iHeight * 3;
byte[] PixelValues = new byte[iBytes];
int iPoint = 0;
for (int i = 0; i < iHeight; i++)
for (int j = 0; j < iWidth; j++)
{
int iG = G[i, j];
int iB = B[i, j];
int iR = R[i, j];
PixelValues[iPoint] = Convert.ToByte(iB);
PixelValues[iPoint + 1] = Convert.ToByte(iG);
PixelValues[iPoint + 2] = Convert.ToByte(iR);
iPoint += 3;
}
System.Runtime.InteropServices.Marshal.Copy(PixelValues, 0, iPtr, iBytes);
Result.UnlockBits(bmpData);
return Result;
}//#
public static bool GetGray(Bitmap srcBitmap, out byte [,] gray)
{
Bitmap tempBitmap;
if (srcBitmap.PixelFormat != PixelFormat.Format8bppIndexed)
tempBitmap = ImageProcess.Image.Gray(srcBitmap);
else
tempBitmap = srcBitmap;
int wide = tempBitmap.Width;
int height = tempBitmap.Height;
gray = new byte [height, wide];
BitmapData gbmData = tempBitmap.LockBits(new Rectangle(0, 0, wide, height),
ImageLockMode.ReadWrite, PixelFormat.Format8bppIndexed);
System.IntPtr ScanG = gbmData.Scan0;
int gOffset = gbmData.Stride - wide;
unsafe
{
byte* g = (byte*)(void*)ScanG;
// for each pixel
for (int y = 0; y < height; y++)
{
// for each pixel
for (int x = 0; x < wide; x++, g++)
{
gray[y ,x ] =*g;
}
g += gOffset;
}
}
tempBitmap.UnlockBits(gbmData);
return true ;
}//#
public static Bitmap FromGray(byte [,] Gray)
{
int iWidth = Gray.GetLength(1);
int iHeight = Gray.GetLength(0);
Bitmap dstBitmap = ImageProcess.Image.CreateGrayscaleImage(iWidth, iHeight);
BitmapData gbmData = dstBitmap.LockBits(new Rectangle(0, 0, iWidth, iHeight),
ImageLockMode.ReadWrite, PixelFormat.Format8bppIndexed);
System.IntPtr ScanG = gbmData.Scan0;
int gOffset = gbmData.Stride - iWidth;
unsafe
{
byte* g = (byte*)(void*)ScanG;
// 注意这个地方图像的两维方向与数组两维的方向是转置的关系
for (int i = 0; i < iHeight; i++)
{
for (int j = 0; j < iWidth; j++)
{
*g=(byte )Gray[i, j] ;
g++;
}
g += gOffset;
}
}
dstBitmap.UnlockBits(gbmData);
return dstBitmap;
} //#
/*********************************补充******************************************/
/// <summary>
/// Create and initialize grayscale image
/// </summary>
public static Bitmap CreateGrayscaleImage( int width, int height )
{
// create new image
Bitmap bmp = new Bitmap( width, height, PixelFormat.Format8bppIndexed );
// set palette to grayscale
SetGrayscalePalette( bmp );
// return new image
return bmp;
}//#
/// <summary>
/// Set pallete of the image to grayscale
/// </summary>
public static void SetGrayscalePalette( Bitmap srcImg )
{
// check pixel format
if ( srcImg.PixelFormat != PixelFormat.Format8bppIndexed )
throw new ArgumentException( );
// get palette
ColorPalette cp = srcImg.Palette;
// init palette
for ( int i = 0; i < 256; i++ )
{
cp.Entries[i] = Color.FromArgb( i, i, i );
}
// set palette back
srcImg.Palette = cp;
}//#
/*********************************END********************************************/
哪里有天才，我是把别人喝咖啡的工夫都用在了工作上了。——鲁迅