|File name extension||.pix|
The PCIDSK (PIX) format is fully supported by the GDB library. It is the only format that supports "adding" segments, and one of the few which supports data-description fields to be extracted from and written to the file.
You can perform a variety of database-maintenance operations for PIX files by using the CATALYST Professional File Utility, often found as a Utility command on the File menu of PCI programs, such as CATALYST Professional Focus.
A single PCIDSK file can hold a variety of geospatial data including rasters, bitmaps, vectors, lookup tables (LUT), pseudocolor tables (PCT) and georeferencing information.
To control the raster layout of a PIX file being created, you can use any of the following option strings:
|FILE||PIX file (header) and a separate external file for each raster channel|
|TILED[nnn] [compression] [ENCRYPT=key]||Tiled file|
With the TILED option, you can specify a tile size, in pixels, by entering a number [nnn] immediately after the TILED keyword; otherwise, a default tile size of 256 x 256 is applied.
If you add the ENCRYPT=key option, the image data for the file remains encrypted, based on the key given. This key must be supplied to unencrypt the data. An example is TILED RLE ENCRYPT=password.
Typically, tiles are stored uncompressed, but if a compression keyword is added (separated by a space), the pixel values in the tiles will be compressed. Example values are TILED, TILED512 JPEG, TILED512 QUADTREE, TILED RLE and TILED512 WAVE100.
The WAVE compression option uses JPEG2000 compression technology. It is available for all raster bit depths except for C32S and C32R. But channels that are greater than 16-bit are first converted to a 16-bit representation before being compressed. This means that it is going to work well only when the range of pixel values within one tile is less than 65,536.
The amount of compression can be influenced by specifying a compression quality value between 1 and 100. When no quality value is specified, a default value of 75 is used. For example, WAVE50 would mean that the resultant PIX file would be, at most, 50% of the size of the uncompressed version. Note that WAVE100 will result in lossless JPEG2000 compression.
PCI saves a NoData mask if a NoData value is known at the time of compression. This NoData mask is to ensure that any pixel that was considered NoData before being written to the file is still considered NoData after it is read from the file. Further, no pixel is set to the NoData value if it was not considered NoData at the time of compression. This is necessary to keep the integrity of the NoData pixels.
A WAVE-compressed file is guaranteed to be smaller than the uncompressed version.
Each channel in a GDB PIX file can be a quadtree-compressed image at different quad levels.
Although Quadtree compression is lossless, it provides good compression only with images in which large regions of pixels have the same value, which is typical of pseudocolored or thematic images. The tile is compressed based on the pixel value and regions of pixels with the same value. The compression technique stores only the number of bits required to store the maximum pixel value in a tile. For example, a tile with a maximum pixel value of 1 stores only 1 bit for the pixel value.
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