Support for 16 bit image formats

[pelicanbill]

This ( http://pds-imaging.jpl.nasa.gov/data/mer/spirit/mer2po_0xxx/data/sol0770/edr/2p194722334esfapbcp2592r1m1.img ) file is an example of 16 bit .img data which PyPDS currently cannot decode to an image. Mars products appear to be all 16 bit as far as I can see.

The IMAGE label of the above produces this info:
{'BANDS': '1',
'BAND_STORAGE_TYPE': 'BAND_SEQUENTIAL',
'CHECKSUM': '7.44069e+07',
'FIRST_LINE': '93',
'FIRST_LINE_SAMPLE': '201',
'INTERCHANGE_FORMAT': 'BINARY',
'INVALID_CONSTANT': '0.0',
'LINES': '840',
'LINE_SAMPLES': '624',
'MAXIMUM': '254.0',
'MEAN': '141.955',
'MEDIAN': '148.0',
'MINIMUM': '46.0',
'MISSING_CONSTANT': '0.0',
'SAMPLE_BITS': '16',
'SAMPLE_BIT_MASK': '2#0000000011111111#',
'SAMPLE_TYPE': 'MSB_INTEGER',
'STANDARD_DEVIATION': '27.0024'}

[godber]

This issue is true, however the provided sample image is actually a special case, which I have outlined and explained in #12. I have collected a few simpler sample images to address this problem.

• 1F345867992EFFB0J3P1212L0M1.IMG
• 1N345854840EFFB0IEP1994L0M1.IMG
• 1P345688456EFFB0EJP2363L2C1.IMG (EDIT: Had wrong image, now correct)

All of which can be found here: http://an.rsl.wustl.edu/mer/merbrowser/browserFr.aspx?tab=search&m=MERB