1. Apply two box filters with different size and two 2D Gaussian filters to smooth the images
2. Compare the result images of different filters.
3. The 5*5 box filter works best.

1. Filter the temporal derivative by using a simple 1D Sobel filter and a 1D derivative of a Gaussian with standard deviation varied from 1 to 1.4.
2. The simple 0.5[-1 0 1] filter has the best results for detecting moving objects.

1. First define the threshold as the maximum in average image of each image.
2. Vary the value of threshold to compare the results.

MATLAB