HISTO_DOUBLE

        HISTO_DOUBLE

    Computes the histogram of an image (Y_image) as  a  function  of  a sec-
    ond  one  (Z_image).   This  gives  an  information   similar   to,  but
    slightly different from  the  cross  histogram  (cf  HISTO_CROSS).   The
    program  computes  histogram  of  the mean value and standard deviation.
    The result is a table of 4 Columns, in which
      1)  the  first column contains the mean value of the Y_image  (average
        of all pixels in the Y_image for which the Z_image value is included
        in the corresponding slot)
      2) the second the standard deviation (of the Y_image values).
      3)  the  third  the number of pixels of the Y_image  used  to  compute
        the mean and deviation.
      4) the fourth column contains the histogram abscissa   (actual   value
        of the input Z_image)