OpenCv，EmguCv及.net之间的互动(The Interaction of OpenCv, EmguCv AND .net)
作者：王先荣
前言
在.net中使用OpenCv和EmguCv时，必须在三者支持的图像格式之间进行转换。.net中用Bitmap类来承载图像，OpenCv中用IplImage指针来承载图像，EmguCv中用Image<TColor,TDepth>来承载图像。本文主要讲述如何在IplImage、Image<TColor,TDepth>和Bitmap之间转换。
IplImage <=> MIplImage
MIplImage是IplImage中的托管实现，它是.net与OpenCv之间沟通的桥梁。IplImage指针和MIplImage之间的转换主要用到了Marshal类中的PtrToStructure、StructureToPtr、AllocHGlobal和FreeHGlobal这几个静态方法。
/// <summary>
/// 将MIplImage结构转换到IplImage指针；
/// 注意：指针在使用完之后必须用Marshal.FreeHGlobal方法释放。
/// </summary>
/// <param name="mi">MIplImage对象</param>
/// <returns>返回IplImage指针</returns>
public static IntPtr MIplImageToIplImagePointer(MIplImage mi)
{
IntPtr ptr = Marshal.AllocHGlobal(mi.nSize);
Marshal.StructureToPtr(mi, ptr, false);
return ptr;
}
/// <summary>
/// 将IplImage指针转换成MIplImage结构
/// </summary>
/// <param name="ptr">IplImage指针</param>
/// <returns>返回MIplImage结构</returns>
public static MIplImage IplImagePointerToMIplImage(IntPtr ptr)
{
return (MIplImage)Marshal.PtrToStructure(ptr, typeof(MIplImage));
}
需要注意的是，不能使用 MIplImage * pmi=(MIplImage *)ptr.ToPointer(); 和 IntPtr ptr=&mi; 之类的写法。
IplImage <=> Image<TColor,TDepth>
用了MIplImage的辅助，我们可以很容易实现IplImage指针和Image<TColor,TDepth>之间的转换。
/// <summary>
/// 将IplImage指针转换成Emgucv中的Image对象；
/// 注意：这里需要您自己根据IplImage中的depth和nChannels来决定
/// </summary>
/// <typeparam name="TColor">Color type of this image (either Gray, Bgr, Bgra, Hsv, Hls, Lab, Luv, Xyz or Ycc)</typeparam>
/// <typeparam name="TDepth">Depth of this image (either Byte, SByte, Single, double, UInt16, Int16 or Int32)</typeparam>
/// <param name="ptr">IplImage指针</param>
/// <returns>返回Image对象</returns>
public static Image<TColor, TDepth> IplImagePointerToEmgucvImage<TColor, TDepth>(IntPtr ptr)
where TColor : struct, IColor
where TDepth : new()
{
MIplImage mi = IplImagePointerToMIplImage(ptr);
return new Image<TColor, TDepth>(mi.width, mi.height, mi.widthStep, mi.imageData);
}
/// <summary>
/// 将IplImage指针转换成Emgucv中的IImage接口；
/// 1通道对应灰度图像，3通道对应BGR图像，4通道对应BGRA图像。
/// 注意：3通道可能并非BGR图像，而是HLS,HSV等图像
/// </summary>
/// <param name="ptr">IplImage指针</param>
/// <returns>返回IImage接口</returns>
public static IImage IplImagePointToEmgucvIImage(IntPtr ptr)
{
MIplImage mi = IplImagePointerToMIplImage(ptr);
Type tColor;
Type tDepth;
string unsupportedDepth = "不支持的像素位深度IPL_DEPTH";
string unsupportedChannels = "不支持的通道数（仅支持1，2，4通道）";
switch (mi.nChannels)
{
case 1:
tColor = typeof(Gray);
switch (mi.depth)
{
case IPL_DEPTH.IPL_DEPTH_8U:
tDepth = typeof(Byte);
return new Image<Gray, Byte>(mi.width, mi.height, mi.widthStep, mi.imageData);
case IPL_DEPTH.IPL_DEPTH_16U:
tDepth=typeof(UInt16);
return new Image<Gray, UInt16>(mi.width, mi.height, mi.widthStep, mi.imageData);
case IPL_DEPTH.IPL_DEPTH_16S:
tDepth = typeof(Int16);
return new Image<Gray, Int16>(mi.width, mi.height, mi.widthStep, mi.imageData);
case IPL_DEPTH.IPL_DEPTH_32S:
tDepth = typeof(Int32);
return new Image<Gray, Int32>(mi.width, mi.height, mi.widthStep, mi.imageData);
case IPL_DEPTH.IPL_DEPTH_32F:
tDepth = typeof(Single);
return new Image<Gray, Single>(mi.width, mi.height, mi.widthStep, mi.imageData);
case IPL_DEPTH.IPL_DEPTH_64F:
tDepth = typeof(Double);
return new Image<Gray, Double>(mi.width, mi.height, mi.widthStep, mi.imageData);
default:
throw new NotImplementedException(unsupportedDepth);
}
case 3:
tColor = typeof(Bgr);
switch (mi.depth)
{
case IPL_DEPTH.IPL_DEPTH_8U:
tDepth = typeof(Byte);
return new Image<Bgr, Byte>(mi.width, mi.height, mi.widthStep, mi.imageData);
case IPL_DEPTH.IPL_DEPTH_16U:
tDepth = typeof(UInt16);
return new Image<Bgr, UInt16>(mi.width, mi.height, mi.widthStep, mi.imageData);
case IPL_DEPTH.IPL_DEPTH_16S:
tDepth = typeof(Int16);
return new Image<Bgr, Int16>(mi.width, mi.height, mi.widthStep, mi.imageData);
case IPL_DEPTH.IPL_DEPTH_32S:
tDepth = typeof(Int32);
return new Image<Bgr, Int32>(mi.width, mi.height, mi.widthStep, mi.imageData);
case IPL_DEPTH.IPL_DEPTH_32F:
tDepth = typeof(Single);
return new Image<Bgr, Single>(mi.width, mi.height, mi.widthStep, mi.imageData);
case IPL_DEPTH.IPL_DEPTH_64F:
tDepth = typeof(Double);
return new Image<Bgr, Double>(mi.width, mi.height, mi.widthStep, mi.imageData);
default:
throw new NotImplementedException(unsupportedDepth);
}
case 4:
tColor = typeof(Bgra);
switch (mi.depth)
{
case IPL_DEPTH.IPL_DEPTH_8U:
tDepth = typeof(Byte);
return new Image<Bgra, Byte>(mi.width, mi.height, mi.widthStep, mi.imageData);
case IPL_DEPTH.IPL_DEPTH_16U:
tDepth = typeof(UInt16);
return new Image<Bgra, UInt16>(mi.width, mi.height, mi.widthStep, mi.imageData);
case IPL_DEPTH.IPL_DEPTH_16S:
tDepth = typeof(Int16);
return new Image<Bgra, Int16>(mi.width, mi.height, mi.widthStep, mi.imageData);
case IPL_DEPTH.IPL_DEPTH_32S:
tDepth = typeof(Int32);
return new Image<Bgra, Int32>(mi.width, mi.height, mi.widthStep, mi.imageData);
case IPL_DEPTH.IPL_DEPTH_32F:
tDepth = typeof(Single);
return new Image<Bgra, Single>(mi.width, mi.height, mi.widthStep, mi.imageData);
case IPL_DEPTH.IPL_DEPTH_64F:
tDepth = typeof(Double);
return new Image<Bgra, Double>(mi.width, mi.height, mi.widthStep, mi.imageData);
default:
throw new NotImplementedException(unsupportedDepth);
}
default:
throw new NotImplementedException(unsupportedChannels);
}
}
/// <summary>
/// 将Emgucv中的Image对象转换成IplImage指针；
/// </summary>
/// <typeparam name="TColor">Color type of this image (either Gray, Bgr, Bgra, Hsv, Hls, Lab, Luv, Xyz or Ycc)</typeparam>
/// <typeparam name="TDepth">Depth of this image (either Byte, SByte, Single, double, UInt16, Int16 or Int32)</typeparam>
/// <param name="image">Image对象</param>
/// <returns>返回IplImage指针</returns>
public static IntPtr EmgucvImageToIplImagePointer<TColor, TDepth>(Image<TColor, TDepth> image)
where TColor : struct, IColor
where TDepth : new()
{
return image.Ptr;
}
Image<TColor,TDepth> <=> Bitmap
EmguCv中已经实现了这二者之间的转换，分别是Image<TColor,TDepth>类的下列成员：
(1)public Bitmap Bitmap { get; set; }
该属性可以获取或者设置位图；对于Image<Gray, Byte>, Image<Bgr, Byte> 和 Image<Bgra, Byte>这三种情况效率很高，因为Image<TColor,TDepth>和Bitmap共享数据内存。
(2)public Bitmap ToBitmap(int width,int height)及public Bitmap ToBitmap()方法
(3)public Image(Bitmap bmp)
(4)public Image(int width,int height,int stride,IntPtr scan0)
这个构造函数几乎是万能的，只要您清楚图像的内存分布，以及想要的目的。
IplImage <=> Bitmap
IplImage指针和Bitmap间的转换有两种方式，第一种是利用Image<TColor,TDepth>作媒介；第二种是自己写转换的方法，例如我写的下列代码：
/// <summary>
/// 将IplImage指针转换成位图对象；
/// 对于不支持的像素格式，可以先使用cvCvtColor函数转换成支持的图像指针
/// </summary>
/// <param name="ptr">IplImage指针</param>
/// <returns>返回位图对象</returns>
public static Bitmap IplImagePointerToBitmap(IntPtr ptr)
{
MIplImage mi = IplImagePointerToMIplImage(ptr);
PixelFormat pixelFormat; //像素格式
string unsupportedDepth = "不支持的像素位深度IPL_DEPTH";
string unsupportedChannels = "不支持的通道数（仅支持1，2，4通道）";
switch(mi.nChannels)
{
case 1:
switch (mi.depth)
{
case IPL_DEPTH.IPL_DEPTH_8U:
pixelFormat = PixelFormat.Format8bppIndexed;
break;
case IPL_DEPTH.IPL_DEPTH_16U:
pixelFormat = PixelFormat.Format16bppGrayScale;
break;
default:
throw new NotImplementedException(unsupportedDepth);
}
break;
case 3:
switch (mi.depth)
{
case IPL_DEPTH.IPL_DEPTH_8U:
pixelFormat = PixelFormat.Format24bppRgb;
break;
case IPL_DEPTH.IPL_DEPTH_16U:
pixelFormat = PixelFormat.Format48bppRgb;
break;
default:
throw new NotImplementedException(unsupportedDepth);
}
break;
case 4:
switch (mi.depth)
{
case IPL_DEPTH.IPL_DEPTH_8U:
pixelFormat = PixelFormat.Format32bppArgb;
break;
case IPL_DEPTH.IPL_DEPTH_16U:
pixelFormat = PixelFormat.Format64bppArgb;
break;
default:
throw new NotImplementedException(unsupportedDepth);
}
break;
default:
throw new NotImplementedException(unsupportedChannels);
}
Bitmap bitmap = new Bitmap(mi.width, mi.height, mi.widthStep, pixelFormat, mi.imageData);
//对于灰度图像，还要修改调色板
if (pixelFormat == PixelFormat.Format8bppIndexed)
SetColorPaletteOfGrayscaleBitmap(bitmap);
return bitmap;
}
/// <summary>
/// 将位图转换成IplImage指针
/// </summary>
/// <param name="bitmap">位图对象</param>
/// <returns>返回IplImage指针</returns>
public static IntPtr BitmapToIplImagePointer(Bitmap bitmap)
{
IImage iimage = null;
switch (bitmap.PixelFormat)
{
case PixelFormat.Format8bppIndexed:
iimage = new Image<Gray, Byte>(bitmap);
break;
case PixelFormat.Format16bppGrayScale:
iimage = new Image<Gray, UInt16>(bitmap);
break;
case PixelFormat.Format24bppRgb:
iimage = new Image<Bgr, Byte>(bitmap);
break;
case PixelFormat.Format32bppArgb:
iimage = new Image<Bgra, Byte>(bitmap);
break;
case PixelFormat.Format48bppRgb:
iimage = new Image<Bgr, UInt16>(bitmap);
break;
case PixelFormat.Format64bppArgb:
iimage = new Image<Bgra, UInt16>(bitmap);
break;
default:
Image<Bgra, Byte> tmp1 = new Image<Bgra, Byte>(bitmap.Size);
Byte[, ,] data = tmp1.Data;
for (int i = 0; i < bitmap.Width; i++)
{
for (int j = 0; j < bitmap.Height; j++)
{
Color color = bitmap.GetPixel(i, j);
data[j, i, 0] = color.B;
data[j, i, 1] = color.G;
data[j, i, 2] = color.R;
data[j, i, 3] = color.A;
}
}
iimage = tmp1;
break;
}
return iimage.Ptr;
}
/// <summary>
/// 设置256级灰度位图的调色板
/// </summary>
/// <param name="bitmap"></param>
public static void SetColorPaletteOfGrayscaleBitmap(Bitmap bitmap)
{
PixelFormat pixelFormat = bitmap.PixelFormat;
if (pixelFormat == PixelFormat.Format8bppIndexed)
{
ColorPalette palette = bitmap.Palette;
for (int i = 0; i < palette.Entries.Length; i++)
palette.Entries[i] = Color.FromArgb(255, i, i, i);
bitmap.Palette = palette;
}
}
总算，写完了，打字真累啊。
