Crop bitmap image in memory with Pywin32

Question

I am attempting to take a screenshot of my desktop across multiple monitors using pywin32.

I have the screenshot I need on my third monitor but I only need a certain region of the image.

I am able to crop it when I save the bitmapped image to my hard drive like so:

# initial set up code hooking up pywin32 to the desktop

import win32gui, win32ui, win32con, win32api
hwin = win32gui.GetDesktopWindow()

# example dimensions
width = 800
height = 600
left = 3300
top = 100

hwindc = win32gui.GetWindowDC(hwin)
srcdc = win32ui.CreateDCFromHandle(hwindc)
memdc = srcdc.CreateCompatibleDC()
bmp = win32ui.CreateBitmap()
bmp.CreateCompatibleBitmap(srcdc, width, height)
memdc.SelectObject(bmp)

# saving of the file (what I am currently doing)
bmp.SaveBitmapFile(memdc, 'fullshot.bmp')

# strangely enough this crops the portion I need, 
# but within an image that's the entire length of my desktop
# (not sure how to fix that, you could say this is part of the problem)
memdc.BitBlt((0, 0), (width, height), srcdc, (left, top), win32con.SRCCOPY)


img = Image.open('fullshot.bmp')
img = img.crop((0,0,800,600))
# now the cropped image is in memory but I want just the portion I need without saving it to disk

The bmp is of type 'PyCBitmap'. I've tried np.array(bmp) but this doesn't work either. Is there a way can take the bmp screenshotted by pwin32 and crop it to the dimensions I need within the program memory?

update:

I tried the following code which does not work either. When I try to display it with cv2.imshow('image', img) I get an unresponsive window.

signedIntsArray = bmp.GetBitmapBits(True)
img = np.frombuffer(signedIntsArray, dtype='uint8')
img.shape = (height,width,4)

srcdc.DeleteDC()
memdc.DeleteDC()
win32gui.ReleaseDC(hwin, hwindc)
win32gui.DeleteObject(bmp.GetHandle())

cv2.imshow('image', img)

Q.H. · Accepted Answer · 2018-05-20 18:59:29Z

0

The problem I was having wasn't that the bit of code below wasn't working:

signedIntsArray = bmp.GetBitmapBits(True)
img =  np.frombuffer(signedIntsArray, dtype='uint8')
img.shape = (h,w,4)

when I sent it to the cv2.imshow function as cv2.imshow('image', np.array(img), I realized I needed to set a waitKey:

cv2.imshow('image', np.array(screen_grab()))
cv2.waitKey(0)
cv2.destroyAllWindows()

This gave me what I was looking for. Hopefully this helps somebody in the future.

edited May 20, 2018 at 18:59

answered May 20, 2018 at 0:22

Q.H.

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