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https://en.wikipedia.org/wiki/Depth_map

https://en.wikipedia.org/wiki/Range_imaging

To me, it sounds like they are the same thing, except depth map implies only having the z coordinate info.

But then again, if you have a range image vs depth image, is this something one can tell the difference by examining the data or is the term mostly contextual?

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    $\begingroup$ IMO a depth map and a range image are the same thing and can also be called a z-buffer (one could argue that a depth map needn't be an image, but this is mostly rhetorical). Anyway I cannot make sense of your comment "except depth map implies only having the z coordinate info". The term z-buffer was introduced by the computer graphics community I guess, and later rephrased as depth map (in the line of other maps such as texture, shadow, bump, mip...). Range images are more from the image processing community. $\endgroup$
    – user7657
    Oct 12, 2015 at 9:45
  • $\begingroup$ Can you explain "except depth map implies only having the z coordinate info" ? $\endgroup$
    – user7657
    Oct 12, 2015 at 9:48
  • $\begingroup$ It was poorly phrased, but I think I was trying to say that I got the impression that the term "depth maps" is used more in an uncalibrated setting, i.e. when we don't have the camera intrinsics/extrinsics. I don't know if that's true or not, and now I'm convinced those two terms are almost completely interchangeable. It seemed strange to me that those two wikipedia pages linked don't really refer to each other still. $\endgroup$
    – UXkQEZ7
    Oct 13, 2015 at 11:07
  • $\begingroup$ "is this something one can tell the difference by examining the data or is the term mostly contextual": you can't tell the difference. $\endgroup$
    – user7657
    Oct 13, 2015 at 11:53
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    $\begingroup$ find the right solution at : Depth Image vs Range Image $\endgroup$
    – Kamble Tanaji
    Apr 10, 2017 at 6:31

2 Answers 2

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Your understanding is correct, it's z-values vs distances.

A depth map contains the distances of points in the scene to a plane.

A range image contains the distances of points in the scene to another point. This point is very often the camera's position.

For a depth map the plane that the distances are computed with respect to can be any plane, but it is often parallel to the image plane. Examples of common planes:

  • The image plane
  • The focal plane
  • A plane closer to the object, such that the points closest to the camera have distance zero.

If you of the same scene have:

  • A range image with the distances to the camera
  • A depth map with the distance to the image plane

these two images will look very similar, and it's not possible to conclude whether it's a range image or depth map, unless you have something you know is a plane in the image.

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Range Image:

  • Distances of points to another point, mapped on to a sphere (x,y,z).
  • Range images are for x,y and z dimensions.
  • As I understand, z is relative to a global point coordinate (as are x and y).
  • The term has been used interchangeably with point cloud [2].

Depth Map:

  • Distances of points to a plane (such as the focal plane) (x,y,z).
  • Depth image is only for visualizing range along z-axis.
  • As I understand, z is usually relative to the camera.

Thanks to Kamble Tanaji's comment, which mostly explains this for me.

[2] range-image-vs-the-point-cloud

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