Visualizing depth map

[oscarthorn]

Hi!

I’m having some problems with something that probably is not that hard.

I have a depth map in cv_32fc1 Mat. Each pixel is the distance in meters, 0 represents unknown values.

I’m trying to generate an image like this, white is closer and black is farther (0/unknown is also rendered as black):

I would like the range for the visual to be )0,16) meters.

I have tried normalizing to 0,255 and converting to CV_8UC1 but that did not seem to work.

This code gives me something close but it’s all black or white:
depth.convertTo(depth, CV_8UC1);
cv::equalizeHist(depth, depth);
cv::imshow(“q”, depth);
cv::waitKey(1);

[Mica]

Welcome,

Have you tried colormap?

[oscarthorn]

Thanks!

Yes, I’ve tried normalizing and then applying the jet colormap, but the everything just turns different shades of blue. So the range seems to be incorrect. I tried to fix it by removing outliers so every pixel is in range 0,16 in the depth map. But that did not work either.

[Mica]

//Find automatically the max and the min
double Min, Max;
cv::minMaxLoc(input, &Min, &Max);
int max_int = ceil(Max);
//create a window complete black
cv::Mat win_mat(cv::Size(input.cols, input.rows), CV_8UC3, cv::Scalar(0, 0, 0));
input.convertTo(input, CV_8UC3, 255 / (Max - Min), -255 * Min / (Max - Min));
input.convertTo(input, CV_8UC3);
cv::Mat M;
cv::applyColorMap(input, M, COLORMAP_JET);

I think that will make the colors dispersion better.
Also if you want to change the ground color from JET to any other you can do this:

Mat mask;
inRange(dest, Vec3b(128, 0, 0), Vec3b(128, 0, 0), mask);
M.setTo(Vec3b(255, 255, 255), mask);
imshow(“ColorMap”, M);
waitKey(0);

The example above the blue ground of JET (128, 0 ,0 ) is converted to white.

[crackwitz]

depth = ... # depth in meters, 0 = invalid
valid = (depth != 0) # one shouldn't use exact equality on floats but for synthetic values it's ok
dmin, dmax = 0.0, 16.0
ranged = (depth - dmin) / (dmax - dmin) # dmin -> 0.0, dmax -> 1.0
ranged[ranged < 0] = 0 # saturate
ranged[ranged > 1] = 1
output = 1.0 - ranged # 0 -> white, 1 -> black
output[~valid] = 0 # black out invalid
output **= 1/2.2 # most picture data is gamma-compressed

(equivalent math in C++)

if you want a linear mapping. if you don’t…

you could do something like 1 / x, which has infinite range but a natural cutoff at below 1.0 distance.

or you can do something like x / (x+1) (vary the 1):

[oscarthorn]

Thanks! This works perfectly!