ENVI 5: Pyramids in ENVI 5.0
Pyramids play a key role in the new high performance raster visualization in ENVI 5.0. However, pyramid files built by previous versions of ENVI will not work. Old _pyramid files can be deleted if previous versions of ENVI will not be used. Pyramids are built in ENVI 5.0 when the image is displayed. Native format image files can be processed prior to building pyramids. Non-native formats will need pyramids to be built before running processes such as feature extraction or statistics.
There are multiple pyramid modes in ENVI 5.0 which each exhibit different behaviors:
- No pyramid
- No downsampling is available
- Downsampling exists but no pyramid exists
- Pyramid exists
When no pyramid is available, ENVI 5.0 will generate a pyramid file (.enp) when the image is displayed unless the file is in a format that supports internal pyramids (File/Enterprise GDB, JPIP, OGC WMS/WCS, JPEG2000, MrSID, NITF 2.1 C3/C8).
Downsampling:
Downsampling is the process of retrieving lower resolution data on the fly and is provided in some cases while the pyramid file is building. It will not be available to Windows users who are accessing an image file over a network and for which there are no pyramids.
File formats with internal pyramids will not generate .enp files.
If a pyramid file does not exist and downsampling is not available, the following will also not be available:
- 2D Scatter Plot
- Custom Stretch
- Contrast
If a pyramid or internal pyramid does not exist, regardless of downsampling, the following will not be available:
- Overview Window
- Stretch by View Extent
When a user tries to execute a process that is unavailable due to a lack of pyramids or downsampling, one of three behaviors will be exhibited:
- ENVI will automatically build the pyramids before beginning the process.
- The processes may be grayed out an inaccessible in the Toolbox.
- ENVI will request that the pyramids be built before running the process.
Performance:
To utilize the full capability of the new High Performance Display, set ‘Optimize Display Performance’ to True as well as ‘Copy Pyramids Locally’ to True. These settings can be changed at File > Preferences under Settings > Pyramid.
The default setting for both of the above is False due to the increased size of the new pyramid files. Non-native formats will still include full resolution regardless of preference.
Management:
If the directory in which the image is stored is writeable, an .enp file will be created next to the original file. There may also be an additional .xml file created depending on the format.
If the directory is not writeable, the pyramid file will be created in the Auxiliary File Directory Location (File > Preferences > Directories > Auxiliary File Directory). This file will remain associated with the original file.