The present invention is a method of neural stimulation and more specifically an improved method of providing flexible video/image possessing in a visual prosthesis by providing downloadable video filters. In a visual prosthesis, the input video image will, for the foreseeable future, be higher resolution than the output stimulation of the retina, optic nerve or visual cortex. This is due to limits of electrode array technology and the rapid advancement of video camera technology. It is therefore, advantageous to apply video processing algorithms (filters) to help provide the most useful information to the lower resolution electrode array. Different filters are more effective in different environments and for different subjects. Furthermore, filters will continue to improve over time. Examples of situation dependent filters include reverse image, contrast increasing, edge detection, segmentation using chromatic information and motion detection. Filters loaded in the video processing unit may be selected dynamically to suit the situation or the user's preference. It is therefore advantageous to provide flexibility in applying filters. However, it is also important to maintain the security necessary for a medical device. The present invention provides for an external (not implanted) video processing unit with downloadable video filters.