c#中的Bitmap类型是很重要的类型，常常感到困惑，自己本次做了一些查询与测试，总结如下：
一、主要情况说明
（一）Bitmap类
该类是CLR管理的类型，但其图像数据存储空间是否收到CLR管理不是很清楚。不过在使用的时候，是无需手工调用Dispose来释放数据内存空间的，GC会自动释放内存控件的。当然手工调用Dispose的话，GC确实会释放其数据内存空间的，只不过内存空间是托管的还是非托管的没搞清楚。不过对于使用来说，如果需要及时释放内存空间的话，可以调用Dispose，比如包含在using()中来使用。如果不占用很多内存空间，不调用Dispose也完全没有关系的，不会造成内存泄漏，但尽可能及时Dispose。
（二）Bitmap类的GetHBitmap()方法
IntPtr imagePtr=bitmap.GetHBitmap()；本来以为GetHBitmap（）方法是返回一个指向图像数据的IntPtr而已，然而并不是这样的，实际上是创建新的对象，数据都是完全复制过来，不是指向原来bitmap的数据。
该方法会创建一个新的GDI位图，并将指针（句柄）包装成IntPtr返回。特别要注意的是，这是创建一个新的位图，创建完成后，imagePtr就与原来的bitmap完全没有关系了，新的位图完全占用自己的内存空间。需要注意的是，IntPtr类型变量当离开作用域空间且没有其它对象应用它，GC不会释放其内存空间的，必须由程序员手工释放，即调用DeleteObject（）方法释放。此外，InPtr所指向的数据应该是32位的，即使原来Image是24位的，IntPtr图像也是32位的。
（三）利用imagePtr来创建ImageSource对象
ImageSource imgSource = Imaging.CreateBitmapSourceFromHBitmap(imagePtr, IntPtr.Zero, Int32Rect.Empty, BitmapSizeOptions.FromEmptyOptions());利用imagePtr来创建ImageSource对象，也是一样会创建一个新的imgsource对象且图像数据完全拷贝到新对象中，相当于深拷贝，即整个数据都回拷贝过来，然后imgSource就与imagePtr没有关系了。bitmapSource没有实现IDisposable接口，因此不存在Dispose方法。不过，GC可以释放其内存空间。对于需要及时释放内存空间的，可以直接调用GC.Collect()，注意不要过于频繁调用GC.Collect()，避免影响性能。此外，ImageSource图像所指向的数据应该是32位的，即使原来创建IntPtr的Bitmap是24位的，ImageSource图像也是32位的。
（四）Bitmap.LockBits方法
BitmapData data = bitmap.LockBits(new System.Drawing.Rectangle(0, 0, bitmap.Width, bitmap.Height), ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
该方法本来以为是简单的锁定Bitmap的数据，返回BitmapData对象。（BitmapData对象中有一个Intptr类型的Scan0属性，指向具体数据）。但是，不一定的，不一定的，不一定的…是简单的锁定，也可能新创建数据块并转换数据格式后锁定。MSDN中并没有提及这一点。如果LockBits方法中的PixelFormat参数和原来bitmap的PixelFormat属性相同，则就是简单锁定。如果不同，则格式可以接受（32位和24位互相可以接受，其它没有一一测试），比如原来bitmap的PixelFormat属性是PixelFormat.Format24bppRgb，而LockBits中参数给了PixelFormat.Format32bppRgb，也就是图片明明时24位的，你锁定的时候非要按32位来锁定，那么系统就回创建一个新的IntPtr数据区块，并将原来的24位的数据转换位32位的数据存放中新的IntPtr指针对应的内存中。当后面调用bitmap.UnlockBits(data)的时候，系统会自动释放掉新创建的IntPtr所指向的内存数据块并回收内存。反过来也是一样的，即假设原来是32位的，LockBits中设置为24位，则会新创建一个数据块出来，若也设置位32位的，则不会新创建一个数据块出来。
二、代码测试
以下针对上述问题写了些代码，做了简单测试。测试过程中，利用三张图片，mm2000.bmp（2000*2000像素，24位色，理论上占用约12M空间），mmNew2000.bmp(2000*2000像素，24位色，理论上占用约12M空间),Separator100b24.bmp（100*100像素，24位色，理论上占用约30k空间）。
class Program
{
[DllImport("gdi32")]
static extern int DeleteObject(IntPtr o);
/// <summary>
/// print Memory State and return current memory size
/// </summary>
/// <param name="previousMemory"> Memory Size at previous step</param>
/// <returns>current Memory Size</returns>
private static double PrintMemoryState(double previousMemory)
{
Process CurrentProcess = Process.GetCurrentProcess();
double oldsizeD = previousMemory,
currentSizeD = ((double)CurrentProcess.WorkingSet64) / 1024 / 1024;
string sizeString ="Current Memory Size="+currentSizeD.ToString("F2") + "M ";//占用内存
double sizeChangedD = currentSizeD - oldsizeD;
string sizeChangedStr = ";sizeChanged=" + (sizeChangedD > 0 ? ("+" + sizeChangedD.ToString("F2")) : sizeChangedD.ToString("F2")) + "M";
Console.WriteLine(sizeString+sizeChangedStr);
Console.WriteLine();
return currentSizeD;
}
static void Main(string[] args)
{
double previousMemory = 0;
Console.WriteLine("Start Process");
previousMemory = PrintMemoryState(previousMemory);
Console.WriteLine("Just before pic mm2000.bmp is loading");
previousMemory = PrintMemoryState(previousMemory);
//Load pic from file and create a bitmap object,
Bitmap bitmap = (Bitmap)Bitmap.FromFile(@"E:\mm2000.bmp");
Console.WriteLine("Pic mm2000.bmp(2000*2000 RGB24bits) has been loaded to bitmap for 1st time");
Console.WriteLine("PixelFormat=" + bitmap.PixelFormat.ToString());
previousMemory = PrintMemoryState(previousMemory);
bitmap.Dispose();
bitmap = null;
Console.WriteLine(" Pic mm2000.bmp has been unloaded for 1st time");
previousMemory = PrintMemoryState(previousMemory);
bitmap = (Bitmap)Bitmap.FromFile(@"E:\mm2000.bmp");
Console.WriteLine(" Pic file mm2000.bmp(2000*2000 RGB24bits) has been loaded to bitmap for 2nd time");
Console.WriteLine(" PixelFormat=" + bitmap.PixelFormat.ToString());
previousMemory = PrintMemoryState(previousMemory);
Bitmap moreBitmap = (Bitmap)Bitmap.FromFile(@"E:\mm2000.bmp");
Console.WriteLine(" Pic file mm2000.bmp(2000*2000 RGB24bits) has been loaded to moreBitmap for 1st time");
Console.WriteLine(" PixelFormat=" + moreBitmap.PixelFormat.ToString());
previousMemory = PrintMemoryState(previousMemory);
Bitmap moreBitmapNew = (Bitmap)Bitmap.FromFile(@"E:\mmNew2000.bmp");
Console.WriteLine(" Pic file mmNew2000.bmp(2000*2000 RGB24bits) has been loaded to moreBitmapNew for 1st time");
Console.WriteLine(" PixelFormat=" + moreBitmap.PixelFormat.ToString());
previousMemory = PrintMemoryState(previousMemory);
Bitmap more100Bitmap = (Bitmap)Bitmap.FromFile(@"E:\Separator100b24.bmp");
Console.WriteLine("Pic file Separator100b24.bmp(100*100 RGB24bits) has been loaded to more100Bitmap");
Console.WriteLine("PixelFormat=" + moreBitmap.PixelFormat.ToString());
previousMemory = PrintMemoryState(previousMemory);
//Create a New Bitmap with specified PixelFormat
int iwidth = bitmap.Width;
int iHeight = bitmap.Height;
Bitmap bmNew = new Bitmap(iwidth, iHeight, PixelFormat.Format24bppRgb);
Graphics g = Graphics.FromImage(bmNew);
g.DrawImage(bitmap, new System.Drawing.Point(0, 0));
g.Dispose();
Console.WriteLine("New Bitmap bmNew Has been Created");
Console.WriteLine("bmNew PixelFormat=" + bmNew.PixelFormat.ToString());
previousMemory = PrintMemoryState(previousMemory);
BitmapData data = bmNew.LockBits(new System.Drawing.Rectangle(0, 0, bmNew.Width, bmNew.Height), ImageLockMode.ReadOnly, System.Drawing.Imaging.PixelFormat.Format32bppRgb);
Console.WriteLine("bmNew has been locked With parameter PixelFormat=PixelFormat.Format32bppRgb");
Console.WriteLine("The Stride="+ data.Stride);
previousMemory = PrintMemoryState(previousMemory);
bmNew.UnlockBits(data);
Console.WriteLine("bitmapData has been unlocked");
previousMemory = PrintMemoryState(previousMemory);
IntPtr imagePtr = bitmap.GetHbitmap();
Console.WriteLine("imagePtr(IntPtr) has been created from bitmap");
previousMemory = PrintMemoryState(previousMemory);
BitmapSource bitmapSource = System.Windows.Interop.Imaging.CreateBitmapSourceFromHBitmap(imagePtr, IntPtr.Zero, Int32Rect.Empty, BitmapSizeOptions.FromEmptyOptions());
Console.WriteLine("imgsource has been created from imagePtr");
previousMemory = PrintMemoryState(previousMemory);
bitmap.Dispose();
Console.WriteLine("bitmap has been disposed");
previousMemory = PrintMemoryState(previousMemory);
moreBitmap.Dispose();
Console.WriteLine("moreBitmap has been disposed");
previousMemory = PrintMemoryState(previousMemory);
moreBitmapNew.Dispose();
Console.WriteLine("moreBitmapNew has been disposed");
previousMemory = PrintMemoryState(previousMemory);
more100Bitmap.Dispose();
Console.WriteLine("more100Bitmap has been disposed");
previousMemory = PrintMemoryState(previousMemory);
bmNew.Dispose();
Console.WriteLine("bmNew has been disposed");
previousMemory = PrintMemoryState(previousMemory);
bitmapSource = null;
Console.WriteLine("imgsource Has set to null");
previousMemory = PrintMemoryState(previousMemory);
GC.Collect();
GC.WaitForPendingFinalizers();
Console.WriteLine("Garbage Collected,bitmapSource should be realeased");
previousMemory = PrintMemoryState(previousMemory);
DeleteObject(imagePtr);
Console.WriteLine("DeleteObject has been executed,imagePtr data should be realeased");
previousMemory = PrintMemoryState(previousMemory);
Console.WriteLine("Process Ended");
Console.Read();
}
}在上面代码中，对bmNew位图的锁定时，指定了PixelFormat.Format32bppRgb参数，这和bnNew位图自身的格式PixelFormat.Format24bppRgb是不相同的，底层数据存储也是不兼容的。执行后的结果如下所示：
Start Process
Current Memory Size=14.03M ;sizeChanged=+14.03M
Just before pic mm2000.bmp is loading
Current Memory Size=14.52M ;sizeChanged=+0.49M
Pic mm2000.bmp(2000*2000 RGB24bits) has been loaded to bitmap for 1st time
PixelFormat=Format24bppRgb
Current Memory Size=40.59M ;sizeChanged=+26.08M
Pic mm2000.bmp has been unloaded for 1st time
Current Memory Size=17.74M ;sizeChanged=-22.85M
Pic file mm2000.bmp(2000*2000 RGB24bits) has been loaded to bitmap for 2nd time
PixelFormat=Format24bppRgb
Current Memory Size=41.24M ;sizeChanged=+23.50M
Pic file mm2000.bmp(2000*2000 RGB24bits) has been loaded to moreBitmap for 1st time
PixelFormat=Format24bppRgb
Current Memory Size=64.85M ;sizeChanged=+23.61M
Pic file mmNew2000.bmp(2000*2000 RGB24bits) has been loaded to moreBitmapNew for 1st time
PixelFormat=Format24bppRgb
Current Memory Size=88.69M ;sizeChanged=+23.84M
Pic file Separator100b24.bmp(100*100 RGB24bits) has been loaded to more100Bitmap
PixelFormat=Format24bppRgb
Current Memory Size=89.07M ;sizeChanged=+0.38M
New Bitmap bmNew Has been Created
bmNew PixelFormat=Format24bppRgb
Current Memory Size=101.94M ;sizeChanged=+12.87M
bmNew has been locked With parameter PixelFormat=PixelFormat.Format32bppRgb
The Stride=8000
Current Memory Size=118.25M ;sizeChanged=+16.31M
bitmapData has been unlocked
Current Memory Size=103.41M ;sizeChanged=-14.84M
imagePtr(IntPtr) has been created from bitmap
Current Memory Size=122.04M ;sizeChanged=+18.63M
imgsource has been created from imagePtr
Current Memory Size=140.05M ;sizeChanged=+18.01M
bitmap has been disposed
Current Memory Size=117.59M ;sizeChanged=-22.46M
moreBitmap has been disposed
Current Memory Size=94.79M ;sizeChanged=-22.81M
moreBitmapNew has been disposed
Current Memory Size=72.61M ;sizeChanged=-22.17M
more100Bitmap has been disposed
Current Memory Size=72.82M ;sizeChanged=+0.21M
bmNew has been disposed
Current Memory Size=61.67M ;sizeChanged=-11.15M
imgsource Has set to null
Current Memory Size=62.44M ;sizeChanged=+0.77M
Garbage Collected,bitmapSource should be realeased
Current Memory Size=47.57M ;sizeChanged=-14.87M
DeleteObject has been executed,imagePtr data should be realeased
Current Memory Size=32.31M ;sizeChanged=-15.26M
Process Ended从执行结果可以发现：
（1）从文件创建的Bitmap占用内存是位图本身大小的2倍左右，不知道是不是持有文件Stream流导致的。直接创建的Bitmap和位图本身数据大小差不多，从上面的newBM的创建与释放过程的内存变化可以看出来。
（2）由于LockBits中的参数给了32位，而实际位图是24位，因此数据存储是不兼容的，所以发现在LockBits以后，内存增加了16M多一些，UnLockBits后，内存又下降了14M多，推断是系统重新创建了内存区域，并把２４位数据转换位３２位数据存储到锁定区域，UnLockBits时又释放了。当然，如果在LockBits时指定的格式也是24位的，也就是格式和bitmap的格式一致，则测试过程中，内存基本没什么变化。因此，结论是：LockBits中给出的PixelFormat如果与bitmap本身兼容，则不会创建新的数据区块，否则会创建新的数据区块，并在UnLockBits时释放掉。
（3）IntPtr imagePtr=bitmap.GetHBitmap()方法创建了新的位图并且数据是从bitmap完全拷贝到imagePtr所指的新的内存区块中的，并非共享数据的。此外，需要DeleteObject来释放imagePtr，这一点非常重要，否则clr是无法回收内存的。
（4）ImageSource imgSource = Imaging.CreateBitmapSourceFromHBitmap（...）方法创建了imgSource 并且数据是从bitmap完全拷贝到imgSource 所指的新的内存区块中的。clr是可以回收imgSource对象的。
(5)在测试过程中，不同时间执行的结果变化还是又一定差异的，尤其是Bitmap.Dispose()执行后差异较大。这种方式查看内存变化也只能作为参考，不能作为某一个对象具体占用或释放了多少内存的依据。
最后补充：如果上面测试代码中的LockBit修改一下，将指定的32位改为24位，也就是与24位的位图自身的格式相同，如下：
BitmapData data = bmNew.LockBits(new System.Drawing.Rectangle(0, 0, bmNew.Width, bmNew.Height), ImageLockMode.ReadOnly, System.Drawing.Imaging.PixelFormat.Format24bppRgb);
那么针对锁定前后的执行结果如下，可以发现内存变化就很小了：
bmNew has been locked With parameter PixelFormat=PixelFormat.Format32bppRgb
The Stride=6000
Current Memory Size=104.89M ;sizeChanged=+0.41M
bitmapData has been unlocked
Current Memory Size=105.15M ;sizeChanged=+0.26M
