how to measure falling speed of a ball using a dual camera

what feature should i prefer to do this

Answer 1

[Image Analyst]

The centroid is definitely the feature you should measure. You will also need to know the frame times.

[Dan Mathotaarchchi]

What package on matlab should i prefer ?

[Image Analyst]

regionprops() from the Image Processing Toolbox.

[Dan Mathotaarchchi]

is it necessary to use dual camera?. cant it be done using single camera?

[Image Analyst]

If the ball is falling normal to the optic axis, and you have a long enough focal length such that the spatial calibration does not change across the image, then yes you can use a single camera.