what is the difference between optical flow and spatio temporal

Question

I have read about optical flow and spatiotemporal features and found that:

we can get from the optical flow the velocity and orientation of the object, whereas, we can get the location and the time from spatiotemporal.

I got a little bit of confusing that someone use said we can get the same information from both optical flow and spatiotemporal, is that right?

I am just want to know if I was right about what we can get from these both, or they are indicating to the same aim.

Regards

Answer 1

Optical flow is the apparent motion of an object due to a change in the image. For example in the first image a grey spot is left and in the second image it is right. The object thus looks to be moved to the right. However optical flow is only apparent, two mistakes can occur:

1. The object is of a uniform color, and thus there is no apparent motion, even if there is a real one.
2. There is no moving object, but due to for example the change in illumination it looks that way.

On the other hand you have spatio-temporal information. I am not exactly sure about any officially accepted definition, however it seems to me that this is just the combined information of both the position (spatio) of an object at a certain time (temporal). This combination makes an accurate idea of the movement of the object possible.

The way I see it, spatio-temporal information gives you information about the location, velocity, and even the movement vector of the object. The same holds for optical flow, taking into account that there the movement is apparent. Thus, you are almost correct, you only forgot the fact that the optical flow is apparent. Except of course if you just assumed that implicitly, in that case I agree with your explanation.

Edit: to make this more clear, following image. The two different pictures indicate an optical flow, an apparent motion. The cube seems to turn. From optical flow it is not clear if this is also happening in reality. It could be that the camera is moving between the two pictures. However with optical flow we assume that the apparent motion is the result of a real one. This ambiguity we do not have with spatio-temporal information, where our information is always about the reality.

Sources:

Van Gool, L., Tuytelaars, T., Szekely, G., & Ferrari, V. (nd). Pattern Recognition and Image Interpretation: Image processing and Image interpretation.

Picture: http://fzheng.me/2015/03/25/optical-flow/