The driver will automatically convert images whose color space is YCbCr, CMYK or YCbCrK to RGB, unless GDAL_JPEG_TO_RGB is set to NO (YES is the default). When color space translation to RGB is done, the source color space is indicated in the SOURCE_COLOR_SPACE metedata of the IMAGE_STRUCTURE domain.
There is currently no support for georeferencing information or metadata for JPEG files. But if an ESRI world file exists with the .jgw, .jpgw/.jpegw or .wld suffixes, it will be read and used to establish the geotransform for the image. If available a MapInfo .tab file will also be used for georeferencing. Overviews can be built for JPEG files as an external .ovr file.
The driver also supports the "zlib compressed mask appended to the file" approach used by a few data providers to add a bitmask to identify pixels that are not valid data. See RFC 15 for further details.
Starting with GDAL 1.10.1, the driver can deal with bitmask where the bits are ordered with most significant bit first (whereas the usual convention is least significant bit first). The driver will try to autodetect that situation, but the heuristics may fail. In that circumstance, you can set the JPEG_MASK_BIT_ORDER configuration option to MSB. Bitmask can also be completely ignored by specifying JPEG_READ_MASK to NO.
The GDAL JPEG Driver is built using the Independent JPEG Group's jpeg library. Also note that the GeoTIFF driver supports tiled TIFF with JPEG compressed tiles.
To be able to read and write JPEG images with 12-bit sample, you can build GDAL with its internal libjpeg (based on IJG libjpeg-6b, with additional changes for 12-bit sample support), or explicitely pass --with-jpeg12=yes to configure script when building with external libjpeg. See "8 and 12 bit JPEG in TIFF" wiki page for more details.
It is also possible to use the JPEG driver with the libjpeg-turbo, a version of libjpeg, API and ABI compatible with IJG libjpeg-6b, which uses MMX, SSE, and SSE2 SIMD instructions to accelerate baseline JPEG compression/decompression.
Starting with GDAL 1.9.0, XMP metadata can be extracted from the file, and will be stored as XML raw content in the xml:XMP metadata domain.
Starting with GDAL 1.11, GDAL can deal with the following color profile metadata in the COLOR_PROFILE domain:
Note that this metadata property can only be used on the original raw pixel data. If automatic conversion to RGB has been done, the color profile information cannot be used.
This metadata tag can be used as creation options.