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.

1. 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.

2. 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.

Answer 1

This is my solution for python 3.7 and without using PIL

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

i hope that this solutions works for all