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********************************************/