Abstract
A photograph of exterior environment encompassing 120° was taken by an orthographic projection camera, and was converted into the picture of a luminance pattern using colour image processor. In this way the data of luminance in twenty-two natural and artificial landscapes were obtained. Dividing a picture into small areas (about 0.6°) luminance distribution for each scene was plotted as histograms. Based on the shape of histograms, the type of luminance distribution can be classified into four, that is, a natural landscape,, an artificial distant view, an artificial close view and an artificial view with an open plane. Luminance ratios between the adjacent two small areas were then plotted as histograms. This histogram indicates the steepness (or the gentleness) of the slope of brightness, and shows the difference between natural and artificial scenes more clearly. Most luminance ratios for a natural scene are comparatively small, while luminance ratios for an artificial view are either comparatively greater or 1.0 (no contrast). The average of all the luminance ratios between the adjacent two small areas in a picture indicates the harshness (or the flatness) of the total brightness pattern, and differs between natural and artificial scenes. The aver-age of luminance ratios for a natural scene is small, while the average for an artificial view is generally great, with the exception of an artificial view with an open plane. In conclusion, based on the two indices, that is, the steepness of the slope of brightness and the harshness of the total brightness pattern, characteristics of luminance in the exterior environment are satisfactorily explained.
