Courtesy of SOHO/EIT consortium. SOHO is a project of international cooperation between ESA and NASA. This tool is based on an earlier work by J.Shugai.

CH area is measured in relative units, where total area of the Sun equals one unit. Minimal significant area is 0.002 relative units. Average intensity is calculated after filtering and histogram scaling into the range from 0 to 255. Calculation is performed not taking into account correction for spherical shape of the Sun.