Meteosat 4-VIS high-definition imagery was used for testing solar radiation assessment over northeast Brazil during January 1991 and 1994. Actinographs of solarimetric stations in Paraiba State provided proper ground reference. A simple physical model was developed, based on two basic hypotheses: visible and infrared intervals are decoupled, and radiation transfer in the visible interval is essentially conservative. Some ideas are borrowed from the well known model of Gautier et al. for cloudiness assessment. The resulting GL model can run on a personal microcomputer, processing targets of 5 x 5 pixels for all the region. It exhibits rather good behaviour on a monthly scale, reproducing the mean diurnal cycle and assessing mean irradiation with bias and mean standard deviation lower than 10 W m(-2). Fifteen-day means exhibit similar accuracy. Ground albedo is a highly important parameter of the model. As expected, the main sources of error seem to be planetary reflectance and cloudiness assessment, because of the non-lambertian reflection and the different count thresholds for each kind of cloud cover. Further studies considering longer time series of images (VIS and IR channels) as well as the anisotropic properties of finite cloud fields may improve the model.