Convert kinects depth to RGB

Question

I'm using OpenNI and OpenCV (but without the latest code with openni support). If I just send the depth channel to the screen - it will look dark and difficult to understand something. So I want to show a depth channel for the user in a color but cannot find how to do that without losing of accuracy. Now I do it like that:

xn::DepthMetaData xDepthMap;
depthGen.GetMetaData(xDepthMap);
XnDepthPixel* depthData = const_cast<XnDepthPixel*>(xDepthMap.Data());
cv::Mat depth(frame_height, frame_width, CV_16U, reinterpret_cast<void*>(depthData));

cv::Mat depthMat8UC1;
depth.convertTo(depthMat8UC1, CV_8UC1);

cv::Mat falseColorsMap;
cv::applyColorMap(depthMat8UC1, falseColorsMap, cv::COLORMAP_AUTUMN);
depthWriter << falseColorsMap;

But in this case I get worse (loosing details) output than, for instance, kinects software for windows shows me. So I'm looking for a function in OpenNI or OpenCV with a better transformation.

Answer 1

Try this:

const float scaleFactor = 0.05f;
depth.convertTo(depthMat8UC1, CV_8UC1, scaleFactor);
imshow("depth gray",depthMat8UC1);

Play with the value to get a result you're happy with

Answer 2

ghttps://github.com/OpenNI/OpenNI2/blob/master/Samples/Common/OniSampleUtilities.h the link is the code for histogram equalization. In short, it makes the probability of each level equal and optimizes mapping between 10,000 levels and 255 levels. That is why Kinect yellowish map looks better than naive I=255*z/z_range.

NOTE: don’t use color for visualization since a human eye is more sensitive to luminance change than to color variation. So with 255 levels of luminance you will get better contrast than with 255*255*255 levels of color. If you still decide to go along the color mapping avenue use HSV color space where you can manipulate Hue 0..360 deg, Value 1..0 and better set saturation to max. Map depth to hue and value, convert to RGB and display. Than go back to histogram equalization ;)