Each time it's possible to assume a 'reasonable' default value for missing
'mandatory' tag, gdcm does it. <br>
For instance if the Tag 'Samples Per Pixels' is missing, we assume its value is
-'1' (Grey pixels, as opposite to RGB); <br>if the tag 'High Bit' is missing, we
+'1' (Grey pixels, as opposite to RGB); <br>
+if the tag 'High Bit' is missing, we
assume its value is 'Bits stored -1' (i.e. : no bad trick inside the pixels)<br>
As gdcm wants to read *as well* old ACR-NEMA files, it has to be widely
tolerant.