Question

Currently I’m using a pixel reader via AutoItv3 to perform some actions in a program that is running direct X; A game. Right now the program works fine but as an exercise I’ve been rewriting it in python. Right now I can do:

import ImageGrab  # Part of PIL
    image = ImageGrab.grab() #Define an area to capture.
    rgb = image.getpixel((1, 90)) #What pixel do we want?

And that grabs the pixel info I want just fine, but I’m doing this quite rapidly (needs to be done 3x a second or faster), but the result is that it majorly affects the framerate of this DirectX-based game.

Is there a faster way in Python to read a specific screen pixel? Even limiting this one to running every 0.3 seconds is causing more strain than it really should (I actually figured python would be faster than AutoIt for this particular purpose, hence the reason I’m trying it)

Answer 1

This is the PIL’s grabscreen source, Its does not accept any parameters, and Its grab the whole screen and convert it to bitmap.

PyImaging_GrabScreenWin32(PyObject* self, PyObject* args)
{
    int width, height;
    HBITMAP bitmap;
    BITMAPCOREHEADER core;
    HDC screen, screen_copy;
    PyObject* buffer;

    /* step 1: create a memory DC large enough to hold the
       entire screen */

    screen = CreateDC(";DISPLAY", NULL, NULL, NULL); 
    screen_copy = CreateCompatibleDC(screen); 

    width = GetDeviceCaps(screen, HORZRES);
    height = GetDeviceCaps(screen, VERTRES);

    bitmap = CreateCompatibleBitmap(screen, width, height);
    if (!bitmap)
        goto error;

    if (!SelectObject(screen_copy, bitmap))
        goto error;

    /* step 2: copy bits into memory DC bitmap */

    if (!BitBlt(screen_copy, 0, 0, width, height, screen, 0, 0, SRCCOPY))
        goto error;

    /* step 3: extract bits from bitmap */

    buffer = PyString_FromStringAndSize(NULL, height * ((width*3 + 3) & -4));
    if (!buffer)
        return NULL;

    core.bcSize = sizeof(core);
    core.bcWidth = width;
    core.bcHeight = height;
    core.bcPlanes = 1;
    core.bcBitCount = 24;
    if (!GetDIBits(screen_copy, bitmap, 0, height, PyString_AS_STRING(buffer),
                   (BITMAPINFO*) &core, DIB_RGB_COLORS))
        goto error;

    DeleteObject(bitmap);
    DeleteDC(screen_copy);
    DeleteDC(screen);

    return Py_BuildValue("(ii)N", width, height, buffer);

error:
    PyErr_SetString(PyExc_IOError, "screen grab failed");

    DeleteDC(screen_copy);
    DeleteDC(screen);

    return NULL;
}

So, when I just go a little deep, found C approach is good

http://msdn.microsoft.com/en-us/library/dd144909(VS.85).aspx

And Python has ctypes, so here is my approach using ctypes (in Windows 10, winnt has been replaced with Windows):

>>> from ctypes import *
>>> user= windll.LoadLibrary("c:\\winnt\\system32\\user32.dll") #I am in windows 2000, may be yours will be windows
>>> h = user.GetDC(0)
>>> gdi= windll.LoadLibrary("c:\\winnt\\system32\\gdi32.dll")
>>> gdi.GetPixel(h,1023,767)
16777215 #I believe its white color of RGB or BGR value, #FFFFFF (according to msdn it should be RGB)
>>> gdi.GetPixel(h,1024,767)
-1 #because my screen is only 1024x768

You could write a wrapper for function GetPixel like this

from ctypes import windll
dc= windll.user32.GetDC(0)

def getpixel(x,y):
    return windll.gdi32.GetPixel(dc,x,y)

Then you can use like getpixel(0,0), getpixel(100,0), etc…

PS: Mine is Windows 2000, so I put winnt in the path, you may need to change it to windows or you chould completely remove path, just using user32.dll and gdi32.dll should work too.