如何使用opencv（python）从url读取gif

Question

I can read jpg file using cv2 as

import cv2
import numpy as np
import urllib
url = r'http://www.mywebsite.com/abc.jpg'
req = urllib.request.urlopen(url)
arr = np.asarray(bytearray(req.read()), dtype=np.uint8)
img = cv2.imdecode(arr,-1)
cv2.imshow('abc',img)

However, when I do it with gif file, it returns an error:

error: (-215) size.width>0 && size.height>0 in function cv::imshow

How to solve this problem?

Answer 1

Steps:

1. Use urllib to read the gif from web,
2. Use imageio.mimread to load the gif to nump.ndarray (s).
3. Change the channels orders by numpy or OpenCV .
4. Do other image-processing using OpenCV

Code example:

import imageio
import urllib.request

url = "https://i.stack.imgur.com/lui1A.gif"
fname = "tmp.gif"

## Read the gif from the web, save to the disk
imdata = urllib.request.urlopen(url).read()
imbytes = bytearray(imdata)
open(fname,"wb+").write(imdata)

## Read the gif from disk to `RGB`s using `imageio.miread` 
gif = imageio.mimread(fname)
nums = len(gif)
print("Total {} frames in the gif!".format(nums))

# convert form RGB to BGR 
imgs = [cv2.cvtColor(img, cv2.COLOR_RGB2BGR) for img in gif]

## Display the gif
i = 0

while True:
    cv2.imshow("gif", imgs[i])
    if cv2.waitKey(100)&0xFF == 27:
        break
    i = (i+1)%nums
cv2.destroyAllWindows()

---

Note. I use the gif in my another answer. Video Stabilization with OpenCV

The result:

>>> Total 76 frames!

One of the gif-frames displayed: