public long getLongValue() throws ImagingException {
        final Object o = getValue();
        if (o == null) {
            throw new ImagingException("Missing value: " + getTagInfo().getDescription());
        }
        return ((Number) o).longValue();
    }
Gets the value of the field in the form of an eight-byte (long) integer.

@return a signed long integer value.
@throws ImagingException if the field instance is of an incompatible type or does not contain a valid data element.
src/main/java/org/apache/commons/imaging/formats/tiff/TiffField.java