For monitoring (homogeneous) agricultural crops, a quantitative analysis of aerial photography tends to favour black and white multi-spectral aerial photography. For monitoring natural vegetation on the other hand, a visual interpretation may be of primary importance, necessitating false colour photography. If an additional quantitative analysis of false colour photography is required, e.g. for biomass assessment, application of a red filter (FCR) provides a considerable simplification of the analysis, resulting in broad-band red and near-infrared reflectance factors. The reflectance factor in the near-infrared shows a decreased contrast compared with black and white multi-spectral aerial photography. In practical applications, this decrease in contrast with FCR has to be weighed against the possibilities of a visual interpretation.