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Colour inversion issue in Android while streaming via skype!!  - imx6dl controller + ov2685 camera

Question asked by Navinar Savad on Aug 8, 2017
Latest reply on Aug 16, 2017 by Navinar Savad


   I am working on an android device using imx6dl as the microcontroller. I have interfaced an omnivision camera ov2685 with the board. The camera preview is correct, and image capture as well as video capture also works fine using the camera app in the board. The issue is when I call the device from my mobile, pc etc via video calling applications like Skype, Linphone etc, the colors are swapped (The u and v parameters are interchanged).



The camera provides a YUV422 (yuyv) stream to the ipu. This stream is converted to NV12(YUV420) in android and is displayed on the lcd (after conversion to RGB), and while capturing the image, NV12 is compressed and saved in JPEG format. 


Basically, Android uses NV21(YVU420SP) format or YV12(YVU420P) format. But since the imx6dl microcontroller does not support NV21 format, as far as I understand, the freescale Android source code has been modified for NV12. And it does work, when I am opening the camera or accessing it using any other apps in the device only. But when I stream the camera output via skype, then on the other end, the image is inverted. (Essentially, the NV12 image manifests itself as NV21 in the other end). 


 I am assuming that this issue arises because when the NV12 image is streamed through the linphone/skype app, it gets converted to NV21 which is why this inversion occurs.


I verified that the image viewed in the mobile is the inverted one by modifying the NV12 image to YV12 in the device and displaying the inverted image. This one was the same image as seen in the mobile when the NV12 image was streamed. 


Q1. Is there a way to reformat the video stream which is sent via skype? I have been unable to figure out where exactly in android this change should take place (still working on it). A simple interchanging of u and v parameters should do the trick, but the changes I tried to make so far has not had any effect till date.


Q2. Have anyone noticed this issue before? I have not been able to find anyone else who reported this problem. 


Please let me know if you guys have any idea regarding this. I have attached three images below. 

"1.correct_image_in_camera_app.png" -> This is the correct pattern. The image was taken from Camera app in device. 

"2.imx_device_linphone_image.png" -> This is the linphone app in the imx device. The small pattern shown in the low right corner is the correct image also. 

"3.mobile_linphone_stream.jpg" -> This is the linphone app in my smartphone. If you view the images, you can see that the yellow/aqua colors and the red/blue colors seems to be interchanged, as well as a difference in the color tones. This is because the u and v components of the stream from the camera has been swapped. 



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