Convert PyQt5 QPixmap to numpy ndarray

Question

I have pixmap:

pixmap = self._screen.grabWindow(0,
                                 self._x, self._y,
                                 self._width, self._height)

I want to convert it to OpenCV format. I tried to convert it to numpy.ndarray as described here but I got error sip.voidptr object has an unknown size

Is there any way to get numpy array (same format as cv2.VideoCapture read method returns)?

yes. but without success. I don't sure it will work in my case at all — ingvar, Jul 11 '17 at 18:34
Have you verified that QPixmap is valid, have you tried to display or save it to a file? — eyllanesc, Jul 11 '17 at 19:29

score 7 · Accepted Answer · edited Jul 12 '17 at 20:49

7

I got numpy array using this code:

channels_count = 4
pixmap = self._screen.grabWindow(0, self._x, self._y, self._width, self._height)
image = pixmap.toImage()
s = image.bits().asstring(self._width * self._height * channels_count)
arr = np.fromstring(s, dtype=np.uint8).reshape((self._height, self._width, channels_count))

edited Jul 12 '17 at 20:49

eyllanesc

235,170
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answered Jul 12 '17 at 18:43

ingvar

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That indeed worked for me, thanks, however, it raises a DeprecationWarning. It is therefore recommended to replace np.fromstring in your last code line with np.frombuffer. – Shahar Gino Nov 21 '21 at 14:06

score 6 · Answer 2 · answered Apr 25 '18 at 13:07

The copy can be avoided by doing:

channels_count = 4
pixmap = self._screen.grabWindow(0, self._x, self._y, self._width, self._height)
image = pixmap.toImage()
b = image.bits()
# sip.voidptr must know size to support python buffer interface
b.setsize(self._height * self._width * channels_count)
arr = np.frombuffer(b, np.uint8).reshape((self._height, self._width, channels_count))

Ivan · Answer 3 · 2020-06-18T01:42:52.203

1

Heres a function:

def QPixmapToArray(pixmap):
    ## Get the size of the current pixmap
    size = pixmap.size()
    h = size.width()
    w = size.height()

    ## Get the QImage Item and convert it to a byte string
    qimg = pixmap.toImage()
    byte_str = qimg.bits().tobytes()

    ## Using the np.frombuffer function to convert the byte string into an np array
    img = np.frombuffer(byte_str, dtype=np.uint8).reshape((w,h,4))

    return img

edited Jun 18 '20 at 01:42

answered Jun 16 '20 at 07:12

Ivan

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Consider add explanation about your solution, only code answer can be helpful for some, but not for everyone – Reznik Jun 16 '20 at 07:43
Comments added to the answer. – Ivan Jun 18 '20 at 01:45
1

this gives me `AttributeError: 'sip.voidptr' object has no attribute 'tobytes'`. did something change in the framework? – Mark Ch Jul 31 '21 at 21:50
@MarkCh sip.voidptr indicates that its most likely that your QImg is empty. – Ivan Nov 02 '21 at 09:49
@Ivan No it appears when it's non empty – Jedi Knight May 20 '23 at 19:58

Convert PyQt5 QPixmap to numpy ndarray

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