Advanced JPEG 2000 Options

For JPEG 2000 images, you can select JPEG 2000 profiles and other options.

The information included below is provided with the assumption that the user is familiar with the JPEG 2000 standard. Parameter choices accommodated by the JPEG 2000 specification are of such a broad and varied range that it is possible for users to select settings that prove counterproductive to their goals. In particular, some optimal settings can result in degraded decode performance. Considerable trial and error may be required to achieve desired results when diverging from defaults and recommended settings.

A JPEG 2000 image consists of one or more tiles, which are regions of the image that are compressed independently. The order of the resulting “packets” is governed by two settings: Tile Parts and Progression Order. These settings are especially useful to those who need to target specific JP2 workflows.

Profiles

This panel enables you to invoke a list of supported profiles comprised of preset encoding options for particular workflows, and to save your own custom profiles. For more information see Using JPEG 2000 Profiles.

Tile Size

If enabled, the tile size must be no larger than the dimensions of the source image. Smaller tiles reduce the amount of memory required to encode the image, however the use of tiles may introduce edge artifacts.

Tile Parts

Tiles may be written to the JPEG 2000 file sequentially or interleaved. When tiles are interleaved, Tile Parts defines the group of packets that are written together. Tile parts can be grouped by Resolution, Layer, or Component, depending on which Progression Order you use. If you don’t specify a grouping option, the file will be written sequentially.

If an image consists of many tiles, then grouping first by Resolution allows a decoder to display a course resolution of each tile first, and then finer resolutions as more of the file is received.

Some Progression Order options preclude grouping by one or more of the Tile Parts options. For example, the factory default progression order of RPCL sets the Tile Parts option to Resolution, while making the Layout option unavailable and the Component option available.

Progression Order

Progression Order lets you specify the order in which packets will appear in a given file. This facilitates certain workflows. Progression Order may have a significant impact on the time and memory usage required to encode and/or decode the image.

Flush Period

When codestream flushing is enabled, less memory may be required to encode the image. The flush period should be on the order of the strip height being used. Using the flush period should not significantly affect output image quality.

Tile Length Markers

Determines whether or not Tile Length Markers (TLMs) are to be put into the JPEG 2000 codestream. Use of TLMs may provide better decode performance.

Use Packet Length Markers

Enables or disables the use of packet length markers. Use of packet length markers may improve decoding performance.

Use 9-7 Wavelet

Specifies that the floating point 9-7 wavelet be used for encoding, instead of the default integer 5-3 wavelet. The 9-7 wavelet will not encode an image losslessly, however, it may result in a better looking image at higher compression ratios. This option is disabled by default and is only available when the Encode Losslessly option is not selected. By default, the NPJE and EPJE profiles use the 9-7 wavelet.

Codeblock Size

Quality Layers

This value indicates the number of quality layers with which to encode the image. Among other things, quality layers enable better “streaming” (progressive transmission and display) in some applications.

Strip Height (JP2)

Affects memory usage. Increasing this value may improve runtime performance, but at a cost of requiring more physical memory. This value should be decreased when encoding very large images. Changing the strip height does not affect the quality of the output image.

Bits of Precision

Enables you to choose how many significant bits are to be used from the samples of the source imagery. For example, an image may consist of 16-bit data values, but only eleven of those bits may be meaningful.

Default JP2 Settings

The table below lists GeoExpress’s default JP2 settings.

To change these settings, see Preferences.

Option	Setting
Use Tile Size	Enabled
Tile Size	Width: 4096 Height: 4096
Tile Parts	Group by resolution (R)
Code Block Size	Width: 64 Height: 64
Use Precincts	Enabled
Precinct Size	Width: 256 Height: 256
Strip Height	12
Quality Layers	30
Flush Period	Enabled; value: 4096
Tile Length Markers	Enabled; count: 255
Use Packet Length Markers	Enabled
Use 9-7 Wavelet (lossy)	Disabled
Progression Order	RPCL
Use GMLJP2 Metadata	Enabled

Precincts

Using precincts may improve the performance of decode operations for certain image encodings such as those in which tiles are not used. The Precinct Editor enables the user to enter precinct sizes for all of the zoom levels of the image.

Default: GeoExpress uses precincts in which width and height values are both 256.

Precinct sizes must be powers of two, except for the last one in the list, which has the lowest resolution.

GMLJP2 Metadata

Click the GMLJP2 Metadata button to write GML metadata to the JPEG 2000 image or to specify a GML data file.

When you enable the GMLJP2 option, GML metadata is added to the output file according to the GMLJP2 Application Schema version 3.1.1., which can be found at http://schemas.opengis.net/gml/.

If you would rather use an external file that contains all the coverage and other GML data, you may specify that file by deselecting the Write GMLJP2 metadata box option.

Evaluation Order of Metadata

If an external world file is present, its information trumps any metadata. Absent a world file, metadata are evaluated in the following order of priority: