# JP2KAK -- JPEG-2000 (based on Kakadu)

Most forms of JPEG2000 JP2 and JPC compressed images (ISO/IEC 15444-1) can be read with GDAL using a driver based on the Kakadu library. As well, new images can be written. Existing images cannot be updated in place.

The JPEG2000 file format supports lossy and lossless compression of 8bit and 16bit images with 1 or more bands (components). Via the GeoJP2 (tm) mechanism, GeoTIFF style coordinate system and georeferencing information can be embedded within the JP2 file. JPEG2000 files use a substantially different format and compression mechanism than the traditional JPEG compression and JPEG JFIF format. They are distinct compression mechanisms produced by the same group. JPEG2000 is based on wavelet compression.

The JPEG2000 driver documented on this page (the JP2KAK driver) is implemented on top of the commercial Kakadu library. This is a high quality and high performance JPEG2000 library in wide used in the geospatial and general imaging community. However, it is not free, and so normally builds of GDAL from source will not include support for this driver unless the builder purchases a license for the library and configures accordingly. GDAL includes another JPEG2000 driver based on the free JasPer library.

When reading images this driver will represent the bands as being Byte (8bit unsigned), 16 bit signed or 16 bit unsigned. Georeferencing and coordinate system information will be available if the file is a GeoJP2 (tm) file. Files color encoded in YCbCr color space will be automatically translated to RGB. Paletted images are also supported.

Starting with GDAL 1.9.0, XMP metadata can be extracted from JPEG2000 files, and will be stored as XML raw content in the xml:XMP metadata domain.

## Configuration Options

The JP2KAK driver supports the following Config Options. These runtime options can be used to alter the behavior of the driver.

- JP2KAK_THREADS=n: By default an effort is made to take advantage of multi-threading on multi-core computers using default rules from the Kakadu library. This option may be set to a value of zero to avoid using additional threads or to a specific count to create the requested number of worker threads.

- JP2KAK_FUSSY=YES/NO: This can be set to YES to turn on fussy reporting of problems with the JPEG2000 data stream. Defaults to NO.

- JP2KAK_RESILIENT=YES/NO: This can be set to YES to force Kakadu to maximimize resilience with incorrectly created JPEG2000 data files, likely at some cost in performance. This is likely to be necessary if, amoung other reasons, you get an error message about "Expected to find EPH marker following packet header" or error reports indicating the need to run with the resilient and sequential flags on. Defaults to NO.

## Creation Issues

JPEG2000 files can only be created using the CreateCopy mechanism to copy from an existing dataset.

JPEG2000 overviews are maintained as part of the mathematical description of the image. Overviews cannot be built as a separate process, but on read the image will generally be represented as having overview levels at various power of two factors.

Creation Options:

- QUALITY=n: Set the compressed size ratio as a percentage of the size of the uncompressed image. The default is 20 indicating that the resulting image should be 20% of the size of the uncompressed image. Actual final image size may not exactly match that requested depending on various factors. A value of 100 will result in use of the lossless compression algorithm . On typical image data, if you specify a value greater than 65, it might be worth trying with QUALITY=100 instead as lossless compression might produce better compression than lossy compression.

- BLOCKXSIZE=n: Set the tile width to use. Defaults to 20000.

- BLOCKYSIZE=n: Set the tile height to use. Defaults to image height.

- GMLJP2=YES/NO: Indicates whether a GML box conforming to the OGC GML in JPEG2000 specification should be included in the file. Defaults to YES.

- GeoJP2=YES/NO: Indicates whether a GML box conforming to the GeoJP2 (GeoTIFF in JPEG2000) specification should be included in the file. Defaults to YES.

- LAYERS=n: Control the number of layers produced. These are sort of like resolution layers, but not exactly. The default value is 12 and this works well in most situations.

- ROI=xoff,yoff,xsize,ysize: Selects a region to be a region of interest to process with higher data quality. The various "R" flags below may be used to control the amount better. For example the settings "ROI=0,0,100,100", "Rweight=7" would encode the top left 100x100 area of the image with considerable higher quality compared to the rest of the image.

The following creation options are tightly tied to the Kakadu library, and are considered to be for advanced use only. Consult Kakadu documentation to better understand their meaning.

- Corder: Defaults to "PRCL".
- Cprecincts: Defaults to "{512,512},{256,512},{128,512},{64,512},{32,512},{16,512},{8,512},{4,512},{2,512}".
- ORGgen_plt: Defaults to "yes".
- Cmodes: Kakadu library default used.
- Clevels: Kakadu library default used.
- Rshift: Kakadu library default used.
- Rlevels: Kakadu library default used.
- Rweight: Kakadu library default used.

See Also:

- Implemented as `gdal/frmts/jp2kak/jp2kakdataset.cpp`.

- JPEG2000 for Geospatial Applications page, includes GeoJP2(tm) discussion.

- Alternate JPEG200 driver.