This capability is especially useful in creating PCTs for the theme channel output from one of the clustering programs (KCLUS, ISOCLUS, or NGCLUS). In unsupervised classification, the PCT can be passed to the aggregation (labelling) program AGGREG, allowing the user to more readily identify or locate areas. The PCT and theme channel can also represent an 8-bit compression of 24-bit RGB imagery.
See Also: KCLUS, ISOCLUS, NGCLUS, NGCLUS2, MLC, AGGREG, CMPRSS8
Name Prompt Count Type FILE Database File Name 1-64 Char DBIC Database Input Channel List 3 Int DBLUT Database Lookup Table Segment 0-3 Int DBTC Database Theme Channel 1 Int DBPCT Database Pseudocolour Segment 0-1 Int MASK Area Mask (Window or Bitmap) 0-4 Int DBSN Database Segment name 0-8 Char DBSD Database Segment Descriptor 0-64 Char The following parameter receives output: DBPCT Database Pseudocolour Segment 0-1 Int
EASI>FILE="filespec"
EASI>DBIC=r,g,bIf r, g, and b are all the same channel number then this is equivalent to specifying a black and white image. Ranges of channels can be specified with negative values. For example: {2,-4} is internally expanded to {2,3,4}.
EASI>DBLUT=i,j,k | use LUTs to enhance EASI>DBLUT= | no enhancement, use raw RGBRanges of segments can be specified with negative values. For example: {2,-4} is internally expanded to {2,3,4}.
EASI>DBCT=i
EASI>DBPCT=n | overwrite PCT segment n EASI>DBPCT= | create a new segmentIf a new segment is created, then DBPCT is updated with the new segment number when the program completes.
EASI>MASK=xoff,yoff,xsize,ysize | process window
EASI>MASK= b | process only under bitmap
| stored in segment b
EASI>MASK= | process entire image
EASI>DBSN="string"This value is only used if a new pseudocolour segment is created.
EASI>DBSD="string"This value is only used if a new pseudocolour segment is created.
EASI>MONITOR="ON" | turn monitor ON (default)
EASI>MONITOR="OFF" | turn monitor OFF (recommended if
| running in batch/background mode)
Typically the theme channel is the output from one of the clustering programs KCLUS, ISOCLUS, or NGCLUS, and the RGB channels are a visually enhanced version of the channels used in clustering. Other sources can be used as input, however there is no guarantee that the resulting PCT will be meaningful.
The input file (FILE) contains the RGB channels (DBIC) and the theme channel (DBTC) to be used in generating the PCT. An enhancement can be applied to the RGB channels by the use of previously saved Lookup Tables (DBLUT) held in segments on the input file. The generated PCT is saved in a segment on the input file. This can either overwrite an existing PCT or a new segment can be created (DBPCT). If a new segment is created then an 8 character identifying name (DBSN) and a 64 character descriptor (DBSD) are assigned to it. The input theme and RGB channels are not affected. The only output is the generated PCT.
The MASK parameter controls the area of the image that should be used in collecting statistics for generating the PCT. If no values are specified in MASK the entire image is used. If four values are specified then these are assumed to represent a window on the image. If a single value is specified then this is assumed to be a segment number containing a bitmap, where set (on) bits represent pixels to be used.
A value of black (0,0,0) is assigned to entries in the PCT for values which are not represented in the theme channel.
Input theme and RGB channels should be 8-bit. This restriction is due to the 8-bit nature of a Pseudocolour table. While any type of image channel can be used, values are internally converted to 8-bit data. Using non 8-bit data may result in unexpected or poor results.
PCI extends its thanks to William Aymard of the United States Environmental Protection Agency, Environment Monitoring Systems Laboratory, Las Vegas, Nevada, for suggesting this program.
The common reason to compress 24-bit imagery is to export it to other software systems using special file formats. Since 8-bit display hardware is far more common than 24-bit, many software packages and workstations (for example PCs with VGA cards) work exclusively with this type of data.
The following compression technique can be used:
This is done by scanning the entire image and accumulating counts, and red, green, blue grey level sums for each of the 256 (0 to 255) values in the theme channel. Each pixel in the image is examined, the theme channel contributes the value, the corresponding red, green, and blue grey levels for the pixel are accumulated for the value, and the values count is incremented by one.
When the entire image has been scanned, the pseudocolour table is generated where the Nth entry in the pseudocolour table is theme value N, and the colour entries are the red, green, blue sums divided by the corresponding count. Values which have a count of 0 are assigned the output colour black (i.e., 0, 0, 0).
First the unsupervised classification (clustering) is performed. KCLUS is used, with 64 clusters selected.
EASI>FILE="irvine.pix" EASI>DBIC=1,2,3,4,5 EASI>DBOC=7 EASI>MASK= | whole image EASI>NUMCLUS=64 EASI>SEEDFILE= EASI>MAXITER=10 EASI>MOVETHRS=0.01 EASI>SIGGEN="NO" EASI>REPORT="TERM"If enhancement of raw data is desired, the user can enhance the image and run the VIL program to save the enhanced Lookup tables. See the VIL program documentation for more details.
The program PCTMAKE is used to create a Pseudocolour table matching the true-colour image held in channels 3, 2 and 1. Segments 4, 3, 2 hold Lookup tables which enhance the raw data to improve the image appearance.
EASI>DBIC=3,2,1 EASI>DBLUT=4,3,2 EASI>DBTC=7 EASI>MASK= | whole image EASI>DBPCT= | create new PCT segment EASI>DBSN="TrueColr" EASI>DBSD="True Colour" EASI>RUN PCTMAKEThe results can be seen on the display (if desired):
EASI>DBIC=7 EASI>VDOC=1 EASI>DBIW= EASI>VDOW= EASI>RUN IVI | theme channel to display EASI>RUN IVP | PCT to display EASI>RUN DCP "PD1" | show theme using PCTThe program AGGREG is now run to aggregate (label) clusters.