When a palette file is used for a false color vegetation index, it is possible with these values to control range of index values over which the palette will be applies. For full range, the lower limit should be set to 0, and the upper limit to 255, reflecting an index range of -1.0 to +1.0. To limit the colorized pixels to the positive NDVI values only, the lower limit is raised to 128. This is common practice, since values with NDVI less than 0 are usually not vegetation.