Opencv4android mask for matchTemplate()

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Hi.

I'm trying to speed up matchTemplate() for Android. I have already downsampled the image and template to half the original size, but the matching is still somewhat (understandably) slow on some older devices.

I acknowledged that I can pass in a mask to the matchTemplate() method. I'm trying to utilize this in the following way:

1) I know the location of the object from the previous frame, lets say its (180, 30). 2) I want to search only around some specified distance around this point, rather than the whole frame. 3) I create a region of interest based on this distance.

My question is, how can I utilize this roi such that I can take the current image being searched, and set everything outside the ROI to 0? I can then pass this in as a mask, and thus matchTemplate() would only search the image where pixel values are not 0 (so everything in the ROI)?

I have something such as the following:

cameraFrameROI = new Rect(topLeftX, topLeftY, width, height);
Mat mask = new Mat(mCameraMatResized);
// mask = 0 if not part of ROI, otherwise keep original value
Imgproc.matchTemplate(new Mat(mCameraMatResized, cameraFrameROI), mTemplateMatResized, mResult, mMatchMethod);

But I now need to utilize the ROI to create the actual mask.

Would this speed up template matching, and if so, I'm hoping if anyone can provide pointers.

Thanks.