Comparison Between Guided Filter (Edge Preserving Filter) and Gaussian Filter
Create  a synthetic image with abrupt change form black to white (Better yest from Dark Gray to Bright Gray).  
Add Gaussian Noise to it.
Filter it with Guided Filter and Gaussian Filter.
Look at the results.
Draw a 1D Line which crosses it and look at the Original, Noisy, Filters Guided, Filtered Gaussian.


Here are the results:

Noisy Image





Gaussian Filtered Image





Guided Filtered Image





As one could see, the Gaussian Filter smooth the image across high contrast edges while the Guided Filter keep the edges.

The code is located at GitHub - DSP StackExchange Q29041.