Read a base 64 encoded image from memory using OpenCv python library

Question

I'm working on an app that to do some facial recognition from a webcam stream. I get base64 encoded data uri's of the canvas and want to use it to do something like this:

cv2.imshow('image',img)

The data URI looks something like this:

 data:image/gif;base64,R0lGODlhEAAQAMQAAORHHOVSKudfOulrSOp3WOyDZu6QdvCchPGolfO0o/XBs/fNwfjZ0frl3/zy7////wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAACH5BAkAABAALAAAAAAQABAAAAVVICSOZGlCQAosJ6mu7fiyZeKqNKToQGDsM8hBADgUXoGAiqhSvp5QAnQKGIgUhwFUYLCVDFCrKUE1lBavAViFIDlTImbKC5Gm2hB0SlBCBMQiB0UjIQA7

So, for clarity I've shown what the image looks like so the base64 string is not broken.

<img src="data:image/gif;base64,R0lGODlhEAAQAMQAAORHHOVSKudfOulrSOp3WOyDZu6QdvCchPGolfO0o/XBs/fNwfjZ0frl3/zy7////wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAACH5BAkAABAALAAAAAAQABAAAAVVICSOZGlCQAosJ6mu7fiyZeKqNKToQGDsM8hBADgUXoGAiqhSvp5QAnQKGIgUhwFUYLCVDFCrKUE1lBavAViFIDlTImbKC5Gm2hB0SlBCBMQiB0UjIQA7">

The official doc says, that imread accepts a file path as the argument. From this SO answer, if I do something like:

 import base64
 imgdata = base64.b64decode(imgstring) #I use imgdata as this variable itself in references below
 filename = 'some_image.jpg'
 with open(filename, 'wb') as f:
    f.write(imgdata)

The above code snippet works and the image file gets generated properly. However I don't think so many File IO operations are feasible considering I'd be doing this for every frame of the stream. I want to be able to read the image into the memory directly creating the img object.

I have tried two solutions that seem to be working for some people.

Using PIL reference:
```
pilImage = Image.open(StringIO(imgdata))
npImage = np.array(pilImage)
matImage = cv.fromarray(npImage)
```
I get cv not defined as I have openCV3 installed which is available to me as cv2 module. I tried img = cv2.imdecode(npImage,0), this returns nothing.

Getting the bytes from decoded string and converting it into an numpy array of sorts

file_bytes = numpy.asarray(bytearray(imgdata), dtype=numpy.uint8)
img = cv2.imdecode(file_bytes, 0) #Here as well I get returned nothing

The documentation doesn't really mention what the imdecode function returns. However, from the errors that I encountered, I guess it is expecting a numpy array or a scalar as the first argument. How do I get a handle on that image in memory so that I can do cv2.imshow('image',img) and all kinds of cool stuff thereafter.

I hope I was able to make myself clear.

Thanks for your quick reply @Miki, but np.fromstring doesn't work as well. — Vivek Pradhan
– Vivek Pradhan, Commented Nov 17, 2015 at 11:09
@Divakar, it is the base64 encoded string representing that image — Vivek Pradhan
– Vivek Pradhan, Commented Nov 17, 2015 at 12:28

Philip Ciunkiewicz · Accepted Answer · 2025-04-18 02:24:08Z

41

This is my solution for python 3.7 without using PIL.

import base64

def readb64(uri):
   encoded_data = uri.split(',')[1]
   nparr = np.frombuffer(base64.b64decode(encoded_data), np.uint8)
   img = cv2.imdecode(nparr, cv2.IMREAD_COLOR)
   return img

I hope that this solutions works for all.

edited Apr 18 at 2:24

Philip Ciunkiewicz

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answered Jan 15, 2019 at 19:29

Javier Vallejos

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2 Comments

user256890 Over a year ago

base64.b64decode returns a byte array, so I got it working with np.frombuffer(...) instead of np.fromstring(...)

remarcoble Over a year ago

np.fromstring is deprecated on byte input, instead use np.frombuffer.

Lior · Accepted Answer · 2023-06-06 18:26:29Z

35

(Edit: Updated for python 3) This worked for me on python 3, and doesn't require PIL/pillow or any other dependencies (except cv2):

import cv2
import numpy as np
import base64

def data_uri_to_cv2_img(uri):
    encoded_data = uri.split(',')[1]
    nparr = np.frombuffer(base64.b64decode(encoded_data), np.uint8)
    # old (python 2 version):
    # nparr = np.fromstring(encoded_data.decode('base64'), np.uint8)

    img = cv2.imdecode(nparr, cv2.IMREAD_COLOR)
    return img

data_uri = "data:image/jpeg;base64,/9j/4AAQ..."
img = data_uri_to_cv2_img(data_uri)
cv2.imshow("Image", img)
cv2.waitKey(0)
cv2.destroyAllWindows()

edited Jun 6, 2023 at 18:26

answered Mar 1, 2017 at 17:23

Lior

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4 Comments

Lewen Over a year ago

You saved my life ! I'm (obliged to) using Python 2 on AWS and the first solution kept giving me an error like this: stackoverflow.com/questions/28226308/…

Joe Platano Over a year ago

if returning type(img) i get NoneType. Seems the cv2.imdecode(nparr, cv2.IMREAD_COLOR) does not work as wanted

arqam Over a year ago

@JoePlatano So what is the solution?

remarcoble Over a year ago

np.fromstring is deprecated on byte input, instead use np.frombuffer.

kramer65 · Accepted Answer · 2017-05-09 04:01:38Z

15

You can just use both cv2 and pillow like this:

import base64
from PIL import Image
import cv2
from StringIO import StringIO
import numpy as np

def readb64(base64_string):
    sbuf = StringIO()
    sbuf.write(base64.b64decode(base64_string))
    pimg = Image.open(sbuf)
    return cv2.cvtColor(np.array(pimg), cv2.COLOR_RGB2BGR)

cvimg = readb64('R0lGODlhEAAQAMQAAORHHOVSKudfOulrSOp3WOyDZu6QdvCchPGolfO0o/XBs/fNwfjZ0frl3/zy7////wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAACH5BAkAABAALAAAAAAQABAAAAVVICSOZGlCQAosJ6mu7fiyZeKqNKToQGDsM8hBADgUXoGAiqhSvp5QAnQKGIgUhwFUYLCVDFCrKUE1lBavAViFIDlTImbKC5Gm2hB0SlBCBMQiB0UjIQA7')
cv2.imshow(cvimg)

edited May 9, 2017 at 4:01

kramer65

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answered Jun 20, 2016 at 3:10

Jonno_FTW

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2 Comments

Abhilash Ramteke Over a year ago

Hi, I am running this piece of code but it is throwing: line 9, in readb64 sbuf.write(base64.b64decode(base64_string)) TypeError: string argument expected, got 'bytes' How to fix this?

Jonno_FTW Over a year ago

@AbhilashRamteke change base64_string to base64_string.encode('ascii')

Faizi · Accepted Answer · 2022-02-12 13:29:38Z

0

I found this simple solution.

import cv2
import numpy as np
import base64
image = ""  # raw data with base64 encoding
decoded_data = base64.b64decode(image)
np_data = np.fromstring(decoded_data,np.uint8)
img = cv2.imdecode(np_data,cv2.IMREAD_UNCHANGED)
cv2.imshow("test", img)
cv2.waitKey(0)

Source : https://gist.github.com/HoweChen/7cdd09b08147133d8e1fbe9b52c24768

answered Feb 12, 2022 at 13:29

Faizi

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1 Comment

Lior Over a year ago

This is a duplicate of an existing answer

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