As pointed out in the comments to the accepted answer, it is outdated and no longer functional.
Luckily, I had to solve this very problem using Python 3.7 with OpenCV 4.0 recently.
To handle image loading from an URL or an in-memory buffer, I defined the following two functions:
import urllib.request
import cv2
import numpy as np
def get_opencv_img_from_buffer(buffer, flags):
bytes_as_np_array = np.frombuffer(buffer.read(), dtype=np.uint8)
return cv2.imdecode(bytes_as_np_array, flags)
def get_opencv_img_from_url(url, flags):
req = urllib.request.Request(url)
return get_opencv_img_from_buffer(urllib.request.urlopen(req), flags)
As you can see one depends on the other.
The first one, get_opencv_img_from_buffer, can be used to get an image object from an in-memory buffer. It assumes that the buffer has a read method and that it returns an instance of an object that implements the buffer protocol
The second one, get_opencv_img_from_url, generates an image directly from an URL.
The flags argument is passed on to cv2.imdecode,
which has the following constants predefined in cv2:
- cv2.IMREAD_ANYCOLOR - If set, the image is read in any possible color format.
- cv2.IMREAD_ANYDEPTH - If set, return 16-bit/32-bit image when the input has the corresponding depth, otherwise convert it to 8-bit.
- cv2.IMREAD_COLOR - If set, always convert image to the 3 channel BGR color image.
- cv2.IMREAD_GRAYSCALE - If set, always convert image to the single channel grayscale image (codec internal conversion).
- cv2.IMREAD_IGNORE_ORIENTATION - If set, do not rotate the image according to EXIF's orientation flag.
- cv2.IMREAD_LOAD_GDAL - If set, use the gdal driver for loading the image.
- cv2.IMREAD_REDUCED_COLOR_2 - If set, always convert image to the 3 channel BGR color image and the image size reduced 1/2.
- cv2.IMREAD_REDUCED_COLOR_4 - If set, always convert image to the 3 channel BGR color image and the image size reduced 1/4.
- cv2.IMREAD_REDUCED_COLOR_8 - If set, always convert image to the 3 channel BGR color image and the image size reduced 1/8.
- cv2.IMREAD_REDUCED_GRAYSCALE_2 - If set, always convert image to the single channel grayscale image and the image size reduced 1/2.
- cv2.IMREAD_REDUCED_GRAYSCALE_4 - If set, always convert image to the single channel grayscale image and the image size reduced 1/4.
- cv2.IMREAD_REDUCED_GRAYSCALE_8 - If set, always convert image to the single channel grayscale image and the image size reduced 1/8.
- cv2.IMREAD_UNCHANGED - If set, return the loaded image as is (with alpha channel, otherwise it gets cropped).