JP2KAK plugin does not handle some 12 bit images correctly

[bugbuster]

I just upgraded to GDAL 1.10.1.
I try to convert a 4-band, 12-bit unsigned , tiled, Cycc JP2K image to GTiff.
I observe some discrepancies in the final image with GDAL 1.10.1. In fact, the problem comes from the JP2KAK plugin, which does not read my 12-bit image correctly.
The JP2K image histogram is not computed in the same way when comparing V1.8.0 and V1.10.1.

In particular, the statistic values given by GDAL V1.10.1 are wierd for a 12 bit image :

Min = 0 Max = 65520

I found a patch in method JP2KAKDataset::DirectRasterIO() (changeset #25136) which modifies the number of bits :

  if (precisions[i] == 12)
  {
     precisions[i] = 16;
  }

I commented out these few lines of code and the problem disappeared.

Below are detailled informations about the JP2K image from different GDAL versions.

Gdal V1.8.0 : gdalinfo -hist Snafu.jp2

D:\Data>gdalinfo -hist Snafu.jp2
Driver: JP2KAK/JPEG-2000 (based on Kakadu)

Files: Snafu.jp2
Size is 10500, 11098
Coordinate System is `'
Corner Coordinates:
Upper Left  (    0.0,    0.0)
Lower Left  (    0.0,11098.0)
Upper Right (10500.0,    0.0)
Lower Right (10500.0,11098.0)
Center      ( 5250.0, 5549.0)
Band 1 Block=1024x1024 Type=UInt16, ColorInterp=Red
  256 buckets from -4.125 to 2116.13:
  7162796 1 2 4 1 5 9 5 ...  117 116 107 108 3395
  Overviews: 5250x5549, 2625x2775, 1313x1388, 657x694, 329x347
  Image Structure Metadata:
    NBITS=12
    COMPRESSION=JP2000
...

Gdal V1.10.1 : gdalinfo -hist Snafu.jp2

D:\Data>gdalinfo -hist Snafu.jp2
Driver: JP2KAK/JPEG-2000 (based on Kakadu)
Files: Snafu.jp2
       Snafu.jp2.aux.xml
Size is 10500, 11098
Coordinate System is `'
Metadata:
  Corder=RPCL
Corner Coordinates:
Upper Left  (    0.0,    0.0)
Lower Left  (    0.0,11098.0)
Upper Right (10500.0,    0.0)
Lower Right (10500.0,11098.0)
Center      ( 5250.0, 5549.0)
Band 1 Block=1024x1024 Type=UInt16, ColorInterp=Red
  Min=0.000 Max=65520.000
  Minimum=0.000, Maximum=65520.000, Mean=4929.701, StdDev=2792.112
  256 buckets from -128.471 to 65648.5:
  7162797 5 3 14 18 15473 509125 ...  8 5 3 11 2 171
  Overviews: 5250x5549, 2625x2775, 1313x1388, 657x694, 329x347
  Metadata:
    STATISTICS_MAXIMUM=65520
    STATISTICS_MEAN=4929.7008042976
    STATISTICS_MINIMUM=0
    STATISTICS_STDDEV=2792.1120699711
  Image Structure Metadata:
    COMPRESSION=JP2000
    NBITS=12
    .............

[bugbuster]

JPEG2000 image and aux. files

[bugbuster]

Proposed patch

[bugbuster]

It took me some time to make a small example, as I was working on other stuff.

Attached is a TGZ containing :

• image.jp2 : a small 3-band 12-bit JPEG2000 image
• image.jp2.aux.xml.NOK : image statistics from original gdal V1.10.1 (MAX values are over 2¹²⁾
• image.jp2.aux.xml.OK : image statistics with patched gdal version

Another attached file contains my proposed patch.

[Even Rouault]

Looks reasonable.

trunk r27153 "JP2KAK: remove extension from 12bit to 16bit that was introduced without justification in r25136 (#5328)"