A layer based field that uses a normal map to decide in which direction it should move particles.
                      It uses a normal map as input. The main purpose of this modifier though is to be used in combination with 
                     Optical Flow
                    Use image feedback to convert movement to rgb colors
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Optical Flow
                    Use image feedback to convert movement to rgb colors
                    Read More
                    .
                      Here is a little tutorial to help you use it :