Question

Ok, I’m trying to make a program that finds the position of a colored pixel within the desktop. To do this I make a screenshot of the desktop then go through the pixels and search for the one that has the matching RGB as i need. The only problem is that my program returs strange coordonates X,Y for the found pixel…

#include <stdio.h>
#include <windows.h>
#include <atlimage.h>
#include <iostream>
using namespace std;
struct rgbcolor{
    int red;
    int green;
    int blue;} myColor;
struct point{
        int x;
        int y;
    };
point SearchPixel(int r,int g, int b){
    CImage bitmapzor;
    bitmapzor.Load(("C:\\1.bmp"));
    COLORREF PixColor=0; //This is a color data
    int R=0,G=0,B=0; //These are the channel values
    BYTE* byteptr = (BYTE*)bitmapzor.GetBits();
    int ok=0;
    int pitch = bitmapzor.GetPitch(); //This is a pointer offset to get new line of the bitmap
    //Go through every pixel and compare the RGB code
    for (int i=0; i<bitmapzor.GetWidth();i++)
        for (int j=0; j<bitmapzor.GetHeight();j++)
        {
            B= *(byteptr+pitch*j+3*i);
            G= *(byteptr+pitch*j+3*i+1);
            R= *(byteptr+pitch*j+3*i+2);       
            if(R==r&&G==g&&B==b)
            { point p;
              p.x=i;
              p.y=j;
              cout<<"First pixel found at:\n X:"<<p.x<<"\n Y:"<<p.y<<"\n-----------------\n";
              return p; 
            }
        }
    bitmapzor.Destroy(); //destroy the bitmap
    point p;
    p.x=-1;
    p.y=-1;
    cout<<"Pixel not found!\n";
    return p;

}

bool ScreenCapture(int x, int y, int width, int height, char *filename){
   // get a DC compat. w/ the screen
   HDC hDc = CreateCompatibleDC(0);    

   // make a bmp in memory to store the capture in
   HBITMAP hBmp = CreateCompatibleBitmap(GetDC(0), width, height);   

   // join em up
   SelectObject(hDc, hBmp);   

   // copy from the screen to my bitmap
    BitBlt(hDc, 0, 0, width, height, GetDC(0), x, y, SRCCOPY); 
       CImage image;
        image.Attach(hBmp);
        image.Save(("C:\\1.bmp"), Gdiplus::ImageFormatBMP);
      SearchPixel(myColor.red,myColor.green,myColor.blue);

   // free the bitmap memory
   DeleteObject(hBmp);  

   return 1;
   }

int main()
{   //RGB for the searched color
    myColor.red=200;
    myColor.green=191;
    myColor.blue=231;

    int count=0;
    while(true){
        ScreenCapture(0, 0, 1366, 768, "c:\\1.bmp");
            count++;
        cout<<"Number of searches:"<<count<<"\n\n";
        Sleep(500);
    }
   system("pause");
   return 0;    
}

Answer 1

Ok, finally I found a mistake that I think is the cause of this problem.

The pointer arithmetics:

        B= *(byteptr+pitch*j+3*i);
        G= *(byteptr+pitch*j+3*i+1);
        R= *(byteptr+pitch*j+3*i+2);

Are done for 24bits images, but the screenshot is a 32bits image that means I have to change the multiplier to 4 insteand of 3. That means:

    B= *(byteptr+pitch*j+4*i);
    G= *(byteptr+pitch*j+4*i+1);
    R= *(byteptr+pitch*j+4*i+2);

I think… I’ll be back with an edit if this works or not.

EDIT: Yes it works, it gives the corect pixel position. Thanks everyone for your help 🙂 .