How are NDVI images different from infrared images?
Vegetation is bright when viewed in the near-infrared wavelengths. Color infrared images display infrared light in red, and thus highlight areas of vigorous vegetation. Normalized Difference Vegetation index (NDVI) is produced by subtracting the red reflectance from the infrared reflectance and then dividing by the sum ((IR-Red)/(IR+Red)). This produces a grayscale image which is then colorized to highlight vigor variations. The NDVI image more clearly maps out differences in vegetation vigor and stress due to variations in chlorophyll content than infrared images. Differences in brightness due to sun angle and shading are minimized in the NDVI. Additionally, effects of soil color are reduced. While NDVI images have many advantages, the infrared image contains more detail and therefore can be useful for counting rows and identifying features such as gravel streaks. Color infrared film (as opposed to scientific digital infrared images) is sensitive to a broad range of visible and infrar
