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There are several robotics datasets for SLAM, like this one.

In this webpage you can see that the depth image is scaled by a factor of 5000, so that float depth images can be stored in 16 bit png files:

The depth images are scaled by a factor of 5000, i.e., a pixel value of 5000
in the depth image corresponds to a distance of 1 meter from the camera, 10000
to 2 meter distance, etc. A pixel value of 0 means missing value/no data.

I do not understand why this value is chosen. Why not simply 1000, so that there is a conversion of meters to millimeters?

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PNG does not support float numbers (afaik). Hence the depth value needs to be encoded as a fixed point value. The fixed point was chosen, I guess, to get a good trade-off between accuracy (0.2 mm) and range (13 m).

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  • $\begingroup$ Exactly, instead of saving a float depth image in a xml or yml (ascii), this scaling is used in order to use png files as you say. But can you give a reference for the values that you mention for accuracy/range? Are they just a rule of thumb for robotics, or do you have a specific reference? $\endgroup$ – dim_tz Mar 19 '15 at 19:27
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    $\begingroup$ Rule of thumb, and not universal in robotics. I would say mostly depends on the range of your depth sensor. My guess: they wanted to have a range of 10 m, and then rounded for the step size. $\endgroup$ – Jakob Mar 20 '15 at 7:41

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