Question

I am using a cv::VideoCapture in native code and I am having issues with it :
In android java code, Videocapture gives a Yuv420 frame, in native code it’s a BGR one. Since I need a gray image, having a Yuv image would be better (I read there was no cost in converting Yuv to GRAY).

Here are my questions :

A im using a Asus TF201, acquiring a frame takes about 26ms which is a lot… as the standard android camera API gives Yuv does the native version of VideoCapture performs a conversion ? (which would explain the time cost)

Is it possible to change the format with CV_CAP_PROP_FORMAT ? Whenever I try mycapture.get(CV_CAP_PROP_FORMAT) my app crashes…

EDIT : Andrey Kamaev answered this one. I have to use grab/retrieve methods adding a argument in the second one :

capture.retrieve(frame, CV_CAP_ANDROID_GRAY_FRAME);

Thanks

Answer 1

Look at the OpenCV samples for Android. Most of them are getting gray image from a VideoCapture object:

capture.retrieve(mGray, Highgui.CV_CAP_ANDROID_GREY_FRAME);

Internally this gray image is “converted” from yuv420 frame in the most efficient way – even without extra copying.