6.2.4 Unsigned Integers

  Unsigned sixteen-bit integers can be represented in FITS files by subtracting 32768 from each value (thus offsetting the values into the range of a signed sixteen-bit integer) before writing them to the FITS file. The BZERO keyword (or the TZEROn keyword in the case of binary table columns with TFORMn = 'I') must also be included in the header with its value set to 32768 so that FITS reading software will add this offset to the raw values in the FITS file, thus restoring them to the original unsigned integer values. Unsigned thirty-two-bit integers can be represented in FITS files in a similar way by applying an offset of 2147483648 (2³¹) to the data values.