Emgu CV: 如何有效取得像素值?－天天向上

How to go through each and every pixel of an image efficiently?

專案名稱: SpeedUpPixelAcess

Unmaged code:

第一種方式: MIplImage

(1) MIplImage: managed structure equivalent to IplImage

利用Marshal.PtrToStructure指向來源影像指標img.Ptr, 資料結構型態為 MIplImage,

記得前面強迫轉型(MIplImage)

(2) IntPtr intPtr = mImg.ImageData;
C#利用IntPtr指標型態指向 ImageData: 存放影像像素資料起始位置

(3) byte* ptr = (byte*)intPtr.ToPointer();

影像像素資料為byte, (3)表示將C# intPtr格式轉成C++的byte*指標格式

(4) 可以將(2)(3)變成byte* ptr = (byte*)mImg.ImageData.ToPointer();

再次強調 mImg資料型態為MIplImage

private static void RemoveBGUnmanagedVersion1(Image<Bgr, byte> img)
   {
       MIplImage mImg = (MIplImage)Marshal.PtrToStructure(img.Ptr, typeof(MIplImage));
       int hei = img.Height;
       int wid = img.Width;
       int i, j;
       unsafe
       {
           //IntPtr intPtr = mImg.ImageData;
           //byte* ptr = (byte*)intPtr.ToPointer();
           byte* ptr = (byte*)mImg.ImageData.ToPointer();
           for (j = 0; j < hei; j++)
               for (i = 0; i < wid; i++)
               {
                   ptr[0] = 0;   // remove Blue channel
                   ptr++;
                   ptr[0] = 0;   // remove Green channel
                   ptr++;
                   ptr++;        // do nothing to Red channel
               }
       }
   }

第二種方式: MCvMat

類似第一種方法MIplImage

(1) MCvMat: Mananged structure equivalent to CvMat

利用Marshal.PtrToStructure指向來源影像指標img.Mat.Ptr, 資料結構型態為 MCvMat,

記得前面強迫轉型(MCvMat)

(2) byte* ptr = (byte*)mImg.Data.ToPointer(); 再次強調:其中mImg資料型態為MCvMat

影像像素資料為byte, (3)表示將C# intPtr格式轉成C++的byte*指標格式

private static void RemoveBGUnmanagedVersion12(Image<Bgr, byte> img)
       {
           MCvMat mImg = (MCvMat)Marshal.PtrToStructure(img.Mat.Ptr, typeof(MCvMat));
           int hei = img.Height;
           int wid = img.Width;
           int i, j;
           unsafe
           {
               byte* ptr = (byte*)mImg.Data.ToPointer();
               for (j = 0; j < hei; j++)
                   for (i = 0; i < wid; i++)
                   {
                       ptr[0] = 0;   // remove Blue channel
                       ptr++;
                       ptr[0] = 0;   // remove Green channel
                       ptr++;
                       ptr++;        // do nothing to Red channel
                   }
           }
       }

第三種方式: BitmapData

(1) 採用Image裡面成員Bitmap屬性, 搭配BitmapData資料格式進行感性區域(ROI)內的像素操作, 一般來說

ROI即原始影像大小new Rectangle(0, 0, wid, hei)

(2) BitmapData bmpData = bmp.LockBits(…) 利用LockBits將記憶體中的資料鎖住, 並回傳BitmapData

(3) byte* ptr = (byte*)bmpData.Scan0.ToPointer(); 取得影像陣列起始指標位址,即Scan0.ToPointer

(4) 接下來就可以針對BGR進行讀寫囉

(5) 全部完成後, 將記憶體中資料解鎖: bmp.UnlockBits(bmpData);

private static void RemoveBGUnmanagedVersion2(Image<Bgr, byte> img)
        {
            int hei = img.Height; 
            int wid = img.Width;
            Bitmap bmp = img.Bitmap;
            BitmapData bmpData = bmp.LockBits(new Rectangle(0, 0, wid, hei), ImageLockMode.ReadOnly, img.Bitmap.PixelFormat);
            
        
            int i, j;
           
            unsafe
            {
                //IntPtr bmpDataScan0 = bmpData.Scan0;
                //byte* ptr = (byte*)bmpDataScan0.ToPointer(); 
                byte* ptr = (byte*)bmpData.Scan0.ToPointer();
                for (j = 0; j < hei; j++)
                {
                    for (i = 0; i < wid; i++)
                    {
                        try
                        {
                            ptr[0] = 0;   // remove Blue channel
                            ptr++;
                            ptr[0] = 0;   // remove Green channel
                            ptr++;
                            ptr++;        // do nothing to Red channel
                        }
                        catch (Exception exception) { MessageBox.Show(exception.Message); }
                    }
                }
               
                try
                {
                    bmp.UnlockBits(bmpData); 
                }
                catch (Exception exception) {
                    MessageBox.Show(exception.Message); 
                }
               
            }
        }

==========================================================

Managed code:

第一種方式

像素排列方式: img.Data[row, column, channel]

private static void RemoveBGChannelsMangedVersion1(Image<Bgr, byte> img)
       {
           int hei = img.Height;
           int wid = img.Width;
           int i, j;
           for (j = 0; j < hei; j++)
               for (i = 0; i < wid; i++)
               {
                   img.Data[j, i, 0] = 0;  // remove Blue channel
                   img.Data[j, i, 1] = 0;  // remove Green channel
               }
       }

第二種方式

private static void RemoveBGChannelsMangedVersion2(Image<Bgr, byte> img)
       {
           int hei = img.Height;
           int wid = img.Width;
           int i, j;
           byte[, ,] pImg = img.Data;
           for (j = 0; j < hei; j++)
               for (i = 0; i < wid; i++)
               {
                   pImg[j, i, 0] = 0;  // remove Blue channel
                   pImg[j, i, 1] = 0;  // remove Green channel
                   //pImgCopy[j, i, 2];
               }
       }

==========================================================

彩色轉灰階

private static void RGB2Gray(Bitmap src)
        {
            int wid = src.Width;
            int hei = src.Height;
            int i, j;
            BitmapData bmpData = src.LockBits(new Rectangle(0, 0, src.Width, src.Height), ImageLockMode.ReadWrite, src.PixelFormat);
            unsafe
            {
                byte* ptr = (byte*)bmpData.Scan0;
                double gray;
                for (j = 0; j < hei; j++)
                    for (i = 0; i < wid; i++)
                    {
                        gray = 0.299 * ptr[2] + 0.587 * ptr[1] + 0.114 * ptr[0];
                        ptr[0] = ptr[1] = ptr[2] = (byte)gray;
                        ptr+=3;
                    }
            }
            src.UnlockBits(bmpData);
        }

pixel[i] – pixel[i+1] + 128

int wid = src.Width;
           int hei = src.Height;
           int i, j;
           BitmapData bmpData = src.LockBits(new Rectangle(0, 0, src.Width, src.Height), ImageLockMode.ReadWrite, src.PixelFormat);
           unsafe
           {
               byte* ptr = (byte*)bmpData.Scan0;
               byte* ptrNext = ptr+3;
          
               double gray, grayNext;
               int total = hei * wid;
               //for (j = 0; j < hei; j++)
               //    for (i = 0; i < wid; i++)
               for(i=0; i<total-1;i++)
                   {
                       gray = 0.299 * ptr[2] + 0.587 * ptr[1] + 0.114 * ptr[0];
                       grayNext = 0.299 * ptrNext[2] + 0.587 * ptrNext[1] + 0.114 * ptrNext[0];
                       ptr[0] = ptr[1] = ptr[2] = (byte)(gray - grayNext+128);
                       ptr += 3;
                       ptrNext = ptr + 3;
                   }
           }
           src.UnlockBits(bmpData);