How to read image from buffer using OpenCV?

Question

This is what I have so far... can't figure out how to read image from buffer vs file?

import pyqrcode
import io
from cv2 import cv2

qr = pyqrcode.create("Hello")
buffer = io.BytesIO()
qr.svg(buffer)
# image = cv2.imread(path) // How to read image from buffer instead?
cv2.imshow('Image', image)
cv2.waitKey(0)
cv2.destroyAllWindows()

I don't believe OpenCV can read vector graphics such as SVG, I think it only reads bitmapped graphics - I may be wrong. I suspect you'll either have to get pyqrcode to output a PNG (of which it is capable), or use pyvips or wand to read the SVG. If anyone knows better I am always happy to be corrected. — Mark Setchell
– Mark Setchell, Commented Oct 11, 2020 at 13:17
@MarkSetchell Interesting... thanks for helping out. Would you happen to know how to read qr.png(buffer) using cv2? — sunknudsen
– sunknudsen, Commented Oct 11, 2020 at 14:37
You'll need something like cv2.imdecode(np.array(buffer.getcontents()), cv2.IMREAD_COLOR)) I'm not at a computer to test. You basically need to run cv2.imdecode() on something that looks like bytes or a Numpy array and starts with a PNG signature \x89PNG — Mark Setchell
– Mark Setchell, Commented Oct 11, 2020 at 14:48

sunknudsen · Accepted Answer · 2020-10-13 12:35:50Z

2

The following worked. Thanks Mark!

import pyqrcode
import io
import numpy as np
from cv2 import cv2

buffer = io.BytesIO()
qr = pyqrcode.create("Hello")
qr.png(buffer)
buffer.seek(0)
array = np.asarray(bytearray(buffer.read()), dtype=np.uint8)
image = cv2.imdecode(array, cv2.IMREAD_COLOR)
cv2.imshow('Image', image)
cv2.waitKey(0)
cv2.destroyAllWindows()

edited Oct 13, 2020 at 12:35

answered Oct 11, 2020 at 14:59

sunknudsen

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3 Comments

Mark Setchell Over a year ago

Well done! Thank you for sharing back with the SO community.

sunknudsen Over a year ago

@MarkSetchell Hey Mark, depending on what I feed to np.frombuffer, I am getting ValueError: buffer size must be a multiple of element size. Would you happen to know what is going on?

sunknudsen Over a year ago

@MarkSetchell Fixed the issue thanks to stackoverflow.com/a/47389660/4579271 and updated my answer.

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