In recent years, the introduction of PV (photovoltaic generation) systems has been rapidly expanding to realize a sustainable society. In order to deal with the deterioration of power quality that could occur when a large amount of PV systems is installed, it is necessary to predict the PV power based on the solar irradiance and to select and install system stabilizing devices. Therefore, measuring methods for the solar irradiance by image analysis have been proposed. This paper proposes a measuring method for the solar irradiance at multi-points with different color based image analysis. The proposed method creates estimation models at only an arbitrary point. Then, color values at other points to be measured are extracted and correction values are calculated. By applying correction values to existing estimation models, the solar irradiance at multi-points are measured. The proposed method measured the solar irradiance at the light blue roof, the orange roof and the PV panel points in the image from Nov. 1, 2014 to Nov. 30, 2014. As a result, mean absolute errors between measured values of solar irradiance using a pyranometer and the proposed method at these points were 0.093 kW/m2, 0.093 kW/m2, 0.086 kW/m2, respectively. These were decreased by 58%, 51%, and 45% compared those with using the estimation models without applying correction values, respectively.