There is a bias such that an instrument reading of zero corresponds to about 34 milliAngstroms. The raw data is processed to reduce limb darkening and streaks by forcing the brightest parts of the image to average to zero instrumental units. Prominences are seen at the limb but above the disk, the numerical values are essentially raw brightness scaled to provide a pleasing display. CaII observations Five types of data are recorded using this lower chromosphere line. Only the magnetic field and equivalent width are processed for routine use.
Prominences are visible at the limb but are cut off by a sky threshold.
A median filter of 3 by 3 elements is applied to the raw magnetic image before it is reduced in size. Instrumental units should be multiplied by about 2.15 to convert to gauss. On the disk, the field structures are more diffuse. Both of these effects are the result of the field spreading horizontally with increasing height. The equivalent width image is processed to reduce limb darkening and streaks.