Examples of image calibration for an active day (5 July 2014, upper row) and a quiet day (28 May 2017, lower row) images. First column: Uncalibrated images. Second column: calibration masks representing the solar background. Third column: calibrated images. White circles show the region within 0.4 R_⊙ from the disk center. Color range of pixels is 0.5–1.5. Uncalibrated images and calibration masks were normalized by their median brightness.