The mean of all the pixels in the image contained in buffer 'source' is computed. Use MASK or NOZERO to ignore masked or zero-valued pixels in the computation. PIX=p computes the mean using every p'th pixel in every p'th row, for speed.
The computed mean value is printed at the terminal (unless the SILENT word is given) and is also loaded into the VISTA variable Mn, where 'n' is the image buffer number. (ex: the command MN 1 loads the variable M1. The command MN 31 loads the variable MN31). The value of the mean is also loaded into the variable MEAN.
The mean is used by other commands such as the TV command for a default display range, or the DIVIDE command for rescaling images after flat-field divisions.
See MASK for the operation of the pixel mask.