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use opencv api

0 votes

I am more confortable using OpenCV API, so sometime I need to change frame provided by jevois camera with OpenCV and send it over USB. But it does not work as I am trying to do it.

To reproduce issue, I took PythonTest example, and I changed it little bit.

def process(self, inframe, outframe):
        jevois.LINFO("process with usb")

        # Get the next camera image (may block until it is captured):
        inimg = inframe.get()
        jevois.LINFO("Input image is {} {}x{}".format(jevois.fccstr(inimg.fmt), inimg.width, inimg.height))

        # Get the next available USB output image:
        outimg = outframe.get()
        jevois.LINFO("Output image is {} {}x{}".format(jevois.fccstr(outimg.fmt), outimg.width, outimg.height))

        # Example of getting pixel data from the input and copying to the output:
        jevois.paste(inimg, outimg, 0, 0)

        # We are done with the input image:

        # Example of in-place processing:

        img = jevois.convertToCvRGB(outimg)
        # Example of simple drawings:
            (int(outimg.width/2), int(outimg.height/2)), 
        # jevois.drawCircle(outimg,   int(outimg.width/2), 
        #                             int(outimg.height/2), int(outimg.height/2.2),
        #                             2, jevois.YUYV.White)

        jevois.writeText(outimg, "Hi from Python!", 20, 20, jevois.YUYV.White, jevois.Font.Font10x20)
        # We are done with the output, ready to send it to host over USB:

        # Send a string over serial (e.g., to an Arduino). Remember to tell the JeVois Engine to display those messages,
        # as they are turned off by default. For example: 'setpar serout All' in the JeVois console:
        jevois.sendSerial("DONE frame {}".format(self.frame));
        self.frame += 1


asked Mar 21, 2018 in Programmer Questions by nadirloutfi (230 points)

1 Answer

+1 vote
Best answer
I think the problem is that you are getting the output image twice. We basically support two programming models for python:

- the easy one where you just get and send OpenCV images (numpy arrays).

- the more efficient and more fine-grained one where you get and send JeVois raw images.

In your code, the "outimg=outframe.get()" first requests a raw image buffer to be later sent over USB. But then the "outframe.sendCvBGR(img)" is a combined function that hides all the raw buffer interface from the user and assumes that we will only deal with OpenCV images; hence it will again request a raw buffer, then copy the OpenCV pixel data to it, then send the buffer over USB.

Have a look at this for more explanations on the differences:


To get started, I would recommend doing something like the sanbox module in that doc page. Once you get that working, you can have a look at the section about more fine-grained control if you want to further optimize your code for speed.
answered Mar 21, 2018 by JeVois (46,580 points)
selected Mar 21, 2018 by nadirloutfi