Edge Detection Using C,Win32 SDK and GDI+

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Popularity: 5.54 Rating: 3.96 out of 5

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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

Create a simple Win32 application - select empty project
Add a new file Main.cpp
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

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

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

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.

License

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About the Author

Amol Kakhandki

Member

Amol is currently working for a software company in India.His background is an engineering degree in Industrial Electronics.
He has been implementing projects in COM,DCOM,LDAP using VC++ ,MFC,ATL.
This has to be one of my favorite card - Reward Hotel Starwood Preferred Guest Credit Card. Thanks and enjoy!