Averaging depth pixels && simply printing millimetre depth to console (C++)

Question

Hi guys,

I am trying to do two things here:

1. Do a moving average of the last 10 frames (perhaps a bit too many, given how much processing power it consumes)
2. Simply print out the integer value of a single pixel (because #1 isn't working! All I get is a beige colour.)

Here is my code, which doesn't work:

QByteArray QDepthAverager::getAverageDepthImage()
{
	//For each pixel
	for (int pixel = 0; pixel < 614400; pixel=pixel+2)
		{
			pAverageImage[pixel] = 0;
			//And for each image
			for (int i = 0; i < pImageHistory.size(); i++)
			{
				//Get the average for that pixel.
				pAverageImage[pixel] = pAverageImage[pixel] + pImageHistory.at(i)[pixel];

			}
			pAverageImage[pixel] = pAverageImage[pixel] / pHistoryLength;
		}

	/*const char *data = pImageHistory.at(0).data();
	while (*data) {
		std::cout << "[" << *data << "]\n";
		++data;
	}*/
	std::cout << (pImageHistory.at(0).at(1000)>>3) << "\n";
	//std::cout << "Hello!\n";

	

	return pAverageImage;

}

My first question is, how do I just get each pixel to be the integer, without the player cruft? I am using "NUI_INITIALIZE_FLAG_USES_DEPTH", and I am using a commercial K4W sensor, so I should be able to get 640x480 pixel in the following format:

"If your application included NUI_INITIALIZE_FLAG_USES_DEPTH in the dwFlags argument to NuiInitialize, depth data is returned as a 16-bit value in which the low-order 12 bits (bits 0–11) contain the depth value in millimeters."

I think I am being a bit naieve here, and that some more thinking is involved. Clearly, the numbers I am getting out on the console (which sometimes go into the negatives) indicate that I need to do some bit shifting to turn it into a number which is usable. Perhaps shifting it in one direction to remove the player data, then shifting it back to a workable position would be fine.

I wish I had an easy way to see the binary numbers which it is trying to print, so I could figure out where I'm going wrong.

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Clever, witty forum signature.

Answer 1

Regardless of using, NUI_INITIALIZE_FLAG_USES_DEPTH_AND_PLAYER_INDEX or NUI_INITIALIZE_FLAG_USES_DEPTH, to get the depth value you have to bit shift by 3.

Answer 2

This code:

std::cout << (((unsigned short int)depthFrame.at(30000))>>3) << "\n";

Which is being called every time I receive a frame is outputting the following types of results when I rotate the kinect on a tripod:

http://ideone.com/9oa5k

Not really sure why it jumps down suddenly to near zero, then back up to the 8000s. I definitely do not have 8m between my wall and the camera.

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Clever, witty forum signature.

Answer 3

I'm not precisely sure why you're seeing the values you're seeing (it looks like this might be after the averaging or similar?), but do note that there are sentinel values:

#define NUI_IMAGE_DEPTH_NO_VALUE              0
#define NUI_IMAGE_DEPTH_TOO_FAR_VALUE         (0x0fff << NUI_IMAGE_PLAYER_INDEX_SHIFT)
#define NUI_DEPTH_DEPTH_UNKNOWN_VALUE         (0x1fff << NUI_IMAGE_PLAYER_INDEX_SHIFT)

In particular, Unknown >> 3 is 8191, perhaps that's what you're hitting?  If you don't wish to see these sentinel values, you should be able to just not pass

NUI_IMAGE_STREAM_FLAG_DISTINCT_OVERFLOW_DEPTH_VALUES

... which I'm assuming you are passing today?

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-Adam Smith [MSFT]

Answer 4

Funnily enough, I haven't passed that flag anywhere.

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Answer 5

So now I am just doing:

std::cout << (int)((unsigned short int)castedBuffer[307000]>>3) << "\n";

But the numbers it is giving me are in the range of 0-30. I think I have something wrong somewhere, I think that I am only getting half of the 16 bits promised?

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