i have a problem applying Farnebacks method on a grayscale video

i have a video that contains only gray and black and i apply the farnebacks method but i have an error at frameRGB = readFrame(obj); any ideas what is going wrong?

[Adam]

Since you have given no information then obviously we have no idea what is going on. What is the error? Given the line that is causing your error it appears to be independent of your application of Farnebacks method.

[Walter Roberson]

http://www.mathworks.co.uk/matlabcentral/answers/43073-a-guide-to-tags