Streaming images with HttpResponse?

Alex Karargyris

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Nov 15, 2013, 11:15:21 AM11/15/13

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I have this simple app that I opens webcam and processes the frames using OpenCV. In my views.py I have the following code:

def processImage():

while True:

rval, frame = settings.CAP.read() //Read frames from webcam

gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY) //Make frame grayscale

pil_img = Image.fromarray(gray)

response = HttpResponse(mimetype="image/png")

pil_img.save(response, "PNG")

return response

Although there is a while loop the function runs only once because it is broken by "return response". How could I change the code to make it run constantly?

Jorge Cardoso Leitão

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Nov 15, 2013, 12:08:53 PM11/15/13

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I Alex.

I believe that is not possible with Django views. Views are made for request-response, i.e. the client sends a request, the view returns a response, and that's it, end of connection.

In your case, the server has a stream of data that you want to constantly send to the client. This sounds like a standard problem for using Websockets.

Within Django, there are some apps for using Websockets, even though I don't know how websockets work well for video.

Hope this helps,

Jorge

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Javier Guerra Giraldez

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Nov 15, 2013, 12:53:23 PM11/15/13

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On Fri, Nov 15, 2013 at 12:08 PM, Jorge Cardoso Leitão
<jorgeca...@gmail.com> wrote:
> I believe that is not possible with Django views. Views are made for
> request-response, i.e. the client sends a request, the view returns a
> response, and that's it, end of connection.

i think the WSGI standard does support it, by setting a generator
instead of a string value as the response content.

the generator is a function that yield()s more content each time, so
the HTTP response becomes a stream of data.

but i think you're right that Django doesn't support it.

--
Javier

Tomas Ehrlich

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Nov 15, 2013, 1:05:57 PM11/15/13

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Hi there,
I don't know if it's relevant, I've never used it, but the name sounds promising:

StreamingHttpResponse
https://docs.djangoproject.com/en/dev/ref/request-response/#streaminghttpresponse-objects

Cheers,
Tom

Dne Fri, 15 Nov 2013 12:53:23 -0500
Javier Guerra Giraldez <jav...@guerrag.com> napsal(a):

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Alex Karargyris

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Nov 18, 2013, 10:33:57 AM11/18/13

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Dear all,

Thank you for the help. I managed to setup StreamingHttpResponse to read the images from the media folder. However I believe that there is a syntax error with html code <img>. It doesn't display the image. Any help? I am attaching the code below.Thanks in advance!

def stream_response_generator():

yield "<html><body>\n"

for x in range(1, 10):

rval, frame = settings.CAP.read()

gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

cv2.imwrite('media/image.jpeg', gray, [int(cv2.IMWRITE_JPEG_QUALITY), 90])

time.sleep(.1)

x={"src": "%s/image.jpeg" % (settings.MEDIA_URL), "alt": "Video Frame"}

yield "<img %s/>" % x

yield "</body></html>\n"

def camera(request):

resp = StreamingHttpResponse(stream_response_generator())

return resp

Alex Karargyris

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Nov 18, 2013, 3:56:46 PM11/18/13

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So thanks to Simon I was able to make this work. Here is the code for those who might be interested:

yield "<html>"

yield '<meta http-equiv="refresh" content="0.01" />'

yield "<body>\n"

rval, frame = settings.CAP.read()

gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

cv2.imwrite('media/image.jpeg', gray, [int(cv2.IMWRITE_JPEG_QUALITY), 90])

x={"src": "..%s/image.jpeg" % (settings.MEDIA_URL), "alt": "Video Frame"}

yield '<img src="%(src)s" alt="%(alt)s"/>' % x

yield "</body></html>\n"

However as it doesn't stream the images but instead it saves and the html is refreshed every 0.01 secs. This does not seem to be an elegant solution because a) there is latency and b) the browser keeps reloading constantly. Some of you suggested websockets. Is there some good example for Django + Websockets for streaming images to the browser?

Thanks a lot!

-Alex

On Friday, November 15, 2013 11:15:21 AM UTC-5, Alex Karargyris wrote:

Brian Schott

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Nov 18, 2013, 8:37:19 PM11/18/13

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What are you trying to do? Typical approach would be to use Javascript to pull the images. Take a look at dajaxice.

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