How to read the screen pixels?

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various methods for capturing the screen

I want to read a rectangular area, or whole screen pixels. As if screenshot button was pressed.

How i do this?

Edit: Working code:

void CaptureScreen(char *filename)
{
    int nScreenWidth = GetSystemMetrics(SM_CXSCREEN);
    int nScreenHeight = GetSystemMetrics(SM_CYSCREEN);
    HWND hDesktopWnd = GetDesktopWindow();
    HDC hDesktopDC = GetDC(hDesktopWnd);
    HDC hCaptureDC = CreateCompatibleDC(hDesktopDC);
    HBITMAP hCaptureBitmap = CreateCompatibleBitmap(hDesktopDC, nScreenWidth, nScreenHeight);
    SelectObject(hCaptureDC, hCaptureBitmap); 

    BitBlt(hCaptureDC, 0, 0, nScreenWidth, nScreenHeight, hDesktopDC, 0,0, SRCCOPY|CAPTUREBLT); 

    BITMAPINFO bmi = {0}; 
    bmi.bmiHeader.biSize = sizeof(bmi.bmiHeader); 
    bmi.bmiHeader.biWidth = nScreenWidth; 
    bmi.bmiHeader.biHeight = nScreenHeight; 
    bmi.bmiHeader.biPlanes = 1; 
    bmi.bmiHeader.biBitCount = 32; 
    bmi.bmiHeader.biCompression = BI_RGB; 

    RGBQUAD *pPixels = new RGBQUAD[nScreenWidth * nScreenHeight]; 

    GetDIBits(
        hCaptureDC, 
        hCaptureBitmap, 
        0,  
        nScreenHeight,  
        pPixels, 
        &bmi,  
        DIB_RGB_COLORS
    );  

    // write:
    int p;
    int x, y;
    FILE *fp = fopen(filename, "wb");
    for(y = 0; y < nScreenHeight; y++){
        for(x = 0; x < nScreenWidth; x++){
            p = (nScreenHeight-y-1)*nScreenWidth+x; // upside down
            unsigned char r = pPixels[p].rgbRed;
            unsigned char g = pPixels[p].rgbGreen;
            unsigned char b = pPixels[p].rgbBlue;
            fwrite(fp, &r, 1);
            fwrite(fp, &g, 1);
            fwrite(fp, &b, 1);
        }
    }
    fclose(fp);

    delete [] pPixels; 

    ReleaseDC(hDesktopWnd, hDesktopDC);
    DeleteDC(hCaptureDC);
    DeleteObject(hCaptureBitmap);
}

Starting with your code and omitting error checking ...

// Create a BITMAPINFO specifying the format you want the pixels in.
// To keep this simple, we'll use 32-bits per pixel (the high byte isn't
// used).
BITMAPINFO bmi = {0};
bmi.bmiHeader.biSize = sizeof(bmi.bmiHeader);
bmi.bmiHeader.biWidth = nScreenWidth;
bmi.bmiHeader.biHeight = nScreenHeight;
bmi.bmiHeader.biPlanes = 1;
bmi.bmiHeader.biBitCount = 32;
bmi.bmiHeader.biCompression = BI_RGB;

// Allocate a buffer to receive the pixel data.
RGBQUAD *pPixels = new RGBQUAD[nScreenWidth * nScreenHeight];

// Call GetDIBits to copy the bits from the device dependent bitmap
// into the buffer allocated above, using the pixel format you
// chose in the BITMAPINFO.
::GetDIBits(hCaptureDC,
            hCaptureBitmap,
            0,  // starting scanline
            nScreenHeight,  // scanlines to copy
            pPixels,  // buffer for your copy of the pixels
            &bmi,  // format you want the data in
            DIB_RGB_COLORS);  // actual pixels, not palette references

// You can now access the raw pixel data in pPixels.  Note that they are
// stored from the bottom scanline to the top, so pPixels[0] is the lower
// left pixel, pPixels[1] is the next pixel to the right,
// pPixels[nScreenWidth] is the first pixel on the second row from the
// bottom, etc.

// Don't forget to free the pixel buffer.
delete [] pPixels;

Reading screen pixels fast, Read some of the pixel values, decode their colors, perform a mathematical calculation on them and do something with the result (send it over the  Okay, I am looking for a function or something that will read the color of a certain pixel on my monitor, and when that color is detected, another function will be enabled. I figure using RGB. All


Start here Various methods for capturing the screen

Display resolution, The display resolution or display modes of a digital television, computer monitor or display One use of the term display resolution applies to fixed-pixel-array displays such as plasma display panels (PDP), led to blurring of the color for 320- or 640-wide signals, and made text difficult to read (see second image to right). The first kind of resolution refers to the pixel count which is the number of pixels that form your photo. In order to calculate this resolution you just use the same formula you would use for the area of any rectangle; multiply the length by the height.


Rereading your question, it sounds like we may have gotten off on a tangent with the screen capture. If you just want to check some pixels on the screen, you can use GetPixel.

HDC hdcScreen = ::GetDC(NULL);
COLORREF pixel = ::GetPixel(hdcScreen, x, y);
ReleaseDC(NULL, hdcScreen);
if (pixel != CLR_INVALID) {
  int red = GetRValue(pixel);
  int green = GetGValue(pixel);
  int blue = GetBValue(pixel);
  ...
} else {
  // Error, x and y were outside the clipping region.
}

If you're going to read a lot of pixels, then you're better off with a screen capture and then using GetDIBits. Calling GetPixel zillions of times will be slow.

How to read the color of a pixel, Now you will be able to draw things that depend on things which were previously drawn in the screen. Tags: get, read, pixel. Code editor. You can make changes  When you select a lower resolution than the native resolution, such as selecting 1600 x 900 on a native 1920 x 1080 screen, everything appears larger. This means menus, icons, text, and images all


You make a screenshot with BitBlt(). The size of the shot is set with the nWidth and nHeight arguments. The upper left corner is set with the nXSrc and nYSrc arguments.

Scripting API: Texture2D.ReadPixels, Read pixels from screen into the saved texture data. This will copy a rectangular pixel area from the currently active RenderTexture or the view (specified by the  The number of pixels horizontally and vertically is shown as the screen resolution. Screen resolution is typically written as 1024 x 768 (or 1366 x 768 or 1920 x 1080). This means that the screen has 1024 pixels horizontally and 768 pixels vertically. If you don’t know what your screen resolution is, you can find it with this free tool.


You can use the code below to read the screen pixels:

HWND desktop = GetDesktopWindow();
HDC desktopHdc = GetDC(desktop);
COLORREF color = GetPixel(desktopHdc, x, y);

The PC Graphics Handbook, 12.4.2 Reading Screen Pixels A write routine that accesses the video memory The following code fragment can be used to read the value of a screen pixel into​  Read pixels from screen into the saved texture data. This will copy a rectangular pixel area from the currently active RenderTexture or the view (specified by the source parameter) into the position defined by destX and destY. Both coordinates use pixel space - (0,0) is lower left.


Why Understanding Screen Size and Screen Resolution is Important , How to calculate pixels per inch. You've got to understand the difference between the size of the screen and the dimensions of the screen resolution. Screen  To find the screen resolution setting in Windows 10, 8, or 7, select Change display settings from the left side of the screen. If on Windows 10, also click or tap the Advanced display settings link. Windows Vista users need to use the Display Settings option, while Windows XP users,


How do I get the colour of a screen pixel?, The example here show us how to get the color of a pixel in the screen. We use the Robot.getPixelColor(int x, int y) method to obtain the Color  To change your screen resolution. Open Screen Resolution by clicking the Start button , clicking Control Panel, and then, under Appearance and Personalization, clicking Adjust screen resolution. Click the drop-down list next to Resolution, move the slider to the resolution you want, and then click Apply.


Screen resolution: The ultimate guide, In the meantime, read on to find out everything you need to know about Screen resolution is the number of pixels a screen can show, both