JPEG -- JPEG JFIF File Format
The JPEG JFIF format is supported for reading, and batch writing, but not
update in place. JPEG files are represented as one band (greyscale) or three
band (RGB) datasets with Byte valued bands.
There is currently no support for georeferencing information or metadata for
JPEG files. But if an ESRI world file exists with the .wld or .jgw suffixes,
it will be read and used to establish the geotransform for the image. Overviews
can be built for JPEG files as an external .ovr file.
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.
Creation Options
JPEG files are created using the "JPEG" driver code. Only Byte band types
are supported, and only 1 and 3 band configurations. JPEG file creation
is implemented by the batch (CreateCopy) method.
- WORLDFILE=YES: Force the generation of an associated ESRI world
file (with the extension .wld).
- QUALITY=n: By default the quality flag is set to 75, but this
option can be used to select other values. Values must be in the
range 10-100. Low values result in higher compression ratios, but poorer
image quality. Values above 95 are not meaningfully better quality but
can but substantially larger.
- PROGRESSIVE=ON: Enabled generation of progressive jpegs. In some
cases these will display a reduced resolution image in viewers such as
Netscape, and Internet Explorer, before the full file has been downloaded.
However, some applications cannot read progressive jpegs at all. GDAL can
read progressive jpegs, but takes no advantage of their progressive nature.
See Also: