Portable Measurement of Skylight Luminance Distribution Taking Account of Chromaticity for Color Design

Abstract

In designing the color of outdoor industrial products such as cars and bridges, the optical balance of its model and background photograph (or each frame of the video sequence) needs to be maintained. To irradiate incident light onto a model, obtaining the accurate luminance, L C , of the sun and skylight distribution from all azimuths using luminance signal, E Y , but also video signal, (E R , E G , E B) is important. We propose how to measure skylight luminance distribution promptly with a highly accurate HDR (high dynamic range) according to video signal (E R , E G , E B), whose value is in an appropriate range each other, is guaranteed for different chromaticity of each pixel and luminance signal, E Y. Our method is unlike traditional HDR targeting the luminance distribution of skylight without considering appropriate range of individual video signal (E R , E G , E B) and excluding intensity of direct sunlight. That is, we use portable ND filters together with a digital camera fitted with a fisheye lens to meet the requirements mentioned above. We propose how to calculate 1) highly accurate luminance, L C , in an experiment and 2) the whole range of luminance, L C , of skylight in all azimuths including direct sunlight according to video signal (E R , E G , E B). Then, we display some field experimental results for showing the effectiveness of our method.