托管C++ 图像快速读取

  基于GetPixel 和 SetPixel 速度实在是太慢，处理大点的图片几乎崩溃的速度，幸好有解决方案~

   Bitmap^ bmp = gcnew Bitmap( "y.bmp" );
 
     Rectangle rect = Rectangle(0,0,bmp->Width,bmp->Height);
       System::Drawing::Imaging::BitmapData^ bmpData = bmp->LockBits( rect,   System::Drawing::Imaging::ImageLockMode::ReadWrite, bmp->PixelFormat );

                // Get the address of the first line.
      IntPtr ptr = bmpData->Scan0;

                // Declare an array to hold the bytes of the bitmap.
                // This code is specific to a bitmap with 24 bits per pixels.
      int bytes =   bmpData->Stride  * bmp->Height ;
      array<Byte>^rgbValues = gcnew array<Byte>(bytes);

               // Copy the RGB values into the array.
              //  System::Runtime::InteropServices::Marshal::Copy( ptr, rgbValues, 0, bytes );
      int PixelSize=3;
                // Set every third value to 255. 
      for ( int y = 0; y < bmp->Height; y++ )
      {
       for ( int x = 0; x < bmp->Width; x ++ )
       {
        rgbValues[bmpData->Stride * y + 3*x] = 200;
        rgbValues[bmpData->Stride * y + 3*x + 1] = 200;
        rgbValues[bmpData->Stride * y + 3*x + 2] = 200;

       }
      
      }
             // Copy the RGB values back to the bitmap
     System::Runtime::InteropServices::Marshal::Copy( rgbValues, 0, ptr, bytes );
                 // Unlock the bits.
     bmp->UnlockBits( bmpData );    
     picBox->Image = bmp;
     String^ filename = L"a.jpg";
     bmp->Save(filename);