Setting the Expanded Stretch Option

McIDAS-X versions 2017.2 and later use the MCSTRETCH environment variable and global keyword to determine whether to display/copy image data using the original stretch option that was standard in versions 2017.1 and earlier, or the expanded stretch option that was added in 2017.2. The expanded stretch option increases the detail shown in specific visible, water vapor and short-wave infrared imagery when displayed with IMGDISP or copied to a 1-byte Area file using commands like IMGCOPY with STYPE=VISR or IMGREMAP.

In particular, the expanded stretch option uses stretch tables (SU command) to expand the range of data values in the higher reflectances in visible bands, both colder and warmer temperatures in water vapor bands, and very hot temperatures (often indicative of fires) in short-wave infrared bands over a larger range of 8-bit brightness values. The McIDAS commands and the satellite and band combinations that can use the expanded stretch are listed in the in the file ~mcidas/data/MCSTRETCH.TXT (in McIDAS, run command SEE MCSTRETCH.TXT to view the file).

The default setting on your client workstation is determined by the MCSTRETCH environment variable, which can be set to either EXP (to request the expanded stretch option) or ORIG (to request the original stretch option). If the environment variable is not set, then EXP is assumed. This value is the default for the entire McIDAS-X session. To override the default setting on a command-by-command basis, use the MCSTRETCH global keyword in the AXFORM, GEO, IMGCOPY, IMGDISP, IMGFILT, IMGMAG, IMGOPER, IMGPARM, IMGPROBE, IMGREMAP, IMGRGB, IMGTRACK or LEO command. Note that since the expanded stretch option is available only in versions 2017.2 and later, requests for the expanded stretch will not work if the image specified in your command is located on a remote server running a version earlier than 2017.2. You can, however, first IMGCOPY or IMGREMAP it to your local workstation running 2017.2 or later, then specify the local image in your command requesting the expanded stretch.

If MCSTRETCH is not set on your client workstation, then the expanded stretch option is requested. If you want to be explicit you can set it to EXP by entering the following Unix command (substitute the equivalent if using C shell) on your client workstation.

Type: export MCSTRETCH; MCSTRETCH=EXP

If you want to request the original stretch option, enter the following Unix command (substitute the equivalent if using C shell) on your client workstation.

Type: export MCSTRETCH; MCSTRETCH=ORIG

If you want to set the environment variable each time you log on to your account, add the preferred command of the two above to your $HOME/.mcenv file and add the following line to your $HOME/.profile file. Be sure to leave a space between the period (.) and $HOME.

.  $HOME/.mcenv

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