Edge Detection Using C,Win32 SDK and GDI+

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Introduction

This article is an adaptation of Christian Graus article on the same topic which was in C#. I was keen to do the same in C and hence this article. Though simple I had lot of trouble porting the code from C# to C. I want to take this opportunity to thank Christian for his help in making this program work.

Initializing GDI+

Take the November 2001 platform SDK CD and straight away install the whole thing. Make sure to have gdiplus.dll in your application directory. Also go to tools/options/directories in Visual Studio to point to the GDI+ lib and header files. Important: :They should be at the top of the include list to avoid conflicts.

Includes

1. Create a simple Win32 application - select empty project  
2. Add a new file Main.cpp
3. Include the following:
• ws2_32.lib in the project/settings/link 
• Add this code to your cpp file:

  #define UNICODE
  #include <windows.h>
  #include <gdiplus.h>
  #include <math.h>
  #include <stdio.h>
  using namespace Gdiplus;
  LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM); //WinProc prototype

4. Your WinMain should look like this

   INT WINAPI WinMain(HINSTANCE hInstance, HINSTANCE, PSTR, INT iCmdShow)
   {
      HWND                hWnd;
      MSG                 msg;
      WNDCLASS            wndClass;
      GdiplusStartupInput gdiplusStartupInput;
      ULONG_PTR           gdiplusToken;
   
      // Initialize GDI+.
      GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);
   
      wndClass.style          = CS_HREDRAW | CS_VREDRAW;
      wndClass.lpfnWndProc    = WndProc;
      wndClass.cbClsExtra     = 0;
      wndClass.cbWndExtra     = 0;
      wndClass.hInstance      = hInstance;
      wndClass.hIcon          = LoadIcon(NULL, IDI_APPLICATION);
      wndClass.hCursor        = LoadCursor(NULL, IDC_ARROW);
      wndClass.hbrBackground  = (HBRUSH)GetStockObject(WHITE_BRUSH);
      wndClass.lpszMenuName   = NULL;
      wndClass.lpszClassName  = TEXT("Edge Detection");
   
      RegisterClass(&wndClass);
   
      hWnd = CreateWindow(
         TEXT("Edge Detection"),   // window class name
         TEXT("Edge Detection"),  // window caption
         WS_OVERLAPPEDWINDOW,      // window style
         CW_USEDEFAULT,            // initial x position
         CW_USEDEFAULT,            // initial y position
         CW_USEDEFAULT,            // initial x size
         CW_USEDEFAULT,            // initial y size
         NULL,                     // parent window handle
         NULL,                     // window menu handle
         hInstance,                // program instance handle
         NULL);                    // creation parameters
   
      ShowWindow(hWnd, iCmdShow);
      UpdateWindow(hWnd);
   
      while(GetMessage(&msg, NULL, 0, 0))
      {
         TranslateMessage(&msg);
         DispatchMessage(&msg);
      }
   
      GdiplusShutdown(gdiplusToken);
      return msg.wParam;
   }  // WinMain

5. Your Window procedure should look like this:

   LRESULT CALLBACK WndProc(HWND hWnd, UINT message, 
      WPARAM wParam, LPARAM lParam)
   {
      HDC          hdc;
      PAINTSTRUCT  ps;
   
      switch(message)
      {
      case WM_CREATE:
   		//OnCreate();
   		return 0;
   
      case WM_PAINT:
         hdc = BeginPaint(hWnd, &ps);
         OnPaint(hdc);
         EndPaint(hWnd, &ps);
         return 0;
   
      case WM_DESTROY:
         PostQuitMessage(0);
         return 0;
   
      default:
         return DefWindowProc(hWnd, message, wParam, lParam);
      }
   } // WndProc

6. Your OnPaint() looks like this:

   VOID OnPaint(HDC hdc)
   {	
      Graphics graphics(hdc);
   
      Bitmap b(L"Calvin.jpg");
      Bitmap* b2;
   
      INT iWidth = b.GetWidth();
      INT iHeight = b.GetHeight();
   
      Rect rect(0,0,iWidth,iHeight);
      b2 = b.Clone(rect,PixelFormat24bppRGB); 
   
     
      BitmapData bmData;
      BitmapData bmData2;
   
      b.LockBits(&rect,ImageLockModeRead | ImageLockModeWrite,
                 PixelFormat24bppRGB,&bmData);
      b2->LockBits(&rect,ImageLockModeRead |ImageLockModeWrite,
                   PixelFormat24bppRGB,&bmData2);
      
      int stride = bmData.Stride;
   
      unsigned char * p = (unsigned char *)bmData.Scan0;
      unsigned char * p2 = (unsigned char *)bmData2.Scan0;
      
      
      int nOffset = stride - iWidth*3; 
      int nWidth = iWidth * 3;
   
      int nPixel = 0, nPixelMax = 0;
   
      p += stride;
      p2 += stride;
      int nThreshold = 0;
      
     for(int y=1;y < (iHeight-1);++y)
     {
        p += 3;
        p2 += 3;
   
        for(int x=3; x < (nWidth-3); ++x )
        {  			
   		
           nPixelMax = abs((p2 - stride + 3)[0] - (p2+stride-3)[0]);
           nPixel = abs((p2 + stride + 3)[0] - (p2 - stride - 3)[0]);
           if (nPixel>nPixelMax)
              nPixelMax = nPixel;
   
           nPixel = abs((p2 - stride)[0] - (p2 + stride)[0]);
           if (nPixel>nPixelMax)
               nPixelMax = nPixel;
   
           nPixel = abs((p2+3)[0] - (p2 - 3)[0]);
           if (nPixel>nPixelMax)
               nPixelMax = nPixel;
   
           if (nPixelMax < nThreshold) 
   	    nPixelMax = 0;							
   		
           p[0] = (byte) nPixelMax;
   
           ++ p;
           ++ p2;
               
        }
   
        p += 3 + nOffset;
        p2 += 3 + nOffset;
   }
       
      
      b.UnlockBits(&bmData);
      b2->UnlockBits(&bmData2);
   
      graphics.DrawImage(b2,0,0,iWidth,iHeight);
      graphics.DrawImage(&b, iWidth+10, 0, iWidth, iHeight);      
   
   }

That's It

Write to me for any problems/explanation. I will be glad to respond.