isis2std Documentation

isis2std - Convert ISIS cube to standard image file

This program allows the user to display either a single
selected band of an ISIS cube file as a gray-scale image
or three selected bands as a Red/Green/Blue color
composite image.  The stretch of the single displayed 
band or the stretches of each of the R/G/B color
components can then be interactively adjusted.  The
resulting displayed image can then be written out in a
standard image file format.

If necessary, the displayed image will be subsampled to
fit within a 700x700 display window.  However, the
output file will be generated using the full spatial
resolution of the selected area of the input cube file.

The min/max display range stretch for the image (or each
color component of an R/G/B color composite) is linearly
mapped into 256 intensity levels (8-bit values) for
writing to the output file.  Thus, the full intensity
resolution of the input cube file is used for generating
the output file, subject to the 8-bit resolution
constraint of the output file format (8-bit for each
R/G/B component for a color composite).

Null pixels and low saturation pixels are always
displayed as black (or zero intensity for the color
component in R/G/B mode).  High saturation pixels are
always displayed as white (or maximum intensity for the
component in R/G/B mode).

The program will only work with an 8-bit PsuedoColor
visual type for your display device.  Thus, if you are
running on a 24-bit workstation display, you must type
"device,pseudo=8" after you start up IDL.  (Depending
upon the capabilities of your X server, you might need
to set 8-bit PseudColor as the default visual.)  As a
result of running in 8-bit PseudoColor mode, a 3-band
color composite image will not be displayed on the
screen with a full 256 intensity levels per color
component, and thus the quality of the image contained
in the output file may be better than the image displayed
on the screen.


READING IN A CUBE FILE

After starting up IDL, the "isis2std" program can be run
by simply typing isis2std (without any parameters) at the
IDL prompt.

A file selection panel is displayed that allows
selection of the input cube file.  Next, a parameters
panel is displayed that allows selecting the desired
subarea of the cube file using the SFROM parameter.  The
spatial area that is specified will correspond to the
spatial area that is written to the output file.  Note
that no selection of a subarea in the band dimension
should be specified.  (Only the band(s) to be displayed
will be read into memory.)

The parameters panel also allows specifying the initial
range of pixel values that is to be mapped into the
range of displayable intensities.  If "Specified Range"
is selected for the Range Option, then the "Range Min" and
"Range Max" values directly specify the display range.
(For 3-band color composite mode, the same display range
is used for all three bands.)  If "AUTO Range" is
selected, then the pixels in each input band will be
examined to automatically compute the display range.
(For 3-band color composite mode, the display range is
computed independently for each band.)  The "Low Sat" and
"High Sat" values specify the percent of pixels that are
to be saturated (outside the computed display range) on
the low and high ends.  Note that specifying zero for
"Low Sat" or "High Sat" will cause the computed display
range min or max to be set to the minimum or maximum
values that occur in the selected subarea of the input
band.  When the "AUTO Range" option is selected, the
computed display range is reported on the IDL terminal
window.  The total range of pixel values is reported
in parenthesis.

The parameters panel also allows selecting 1-band
Grayscale mode or RGB Color Composite mode and the band
number to be used.  For 1-band mode, the "R Band" field
specifies the band to be displayed.


CHANGING BAND NUMBERS AND DISPLAY RANGE STRETCH

Along with the displayed image, a plot of the stretch
transfer function is displayed (three plots for the R/G/B
components in color composite mode).  The horizontal
dimension of the plot corresponds to the total range of
pixel values that occurs in the selected band.  Numerical
fields also report the band number and stretch min/max
values.  A new band number or a modified stretch min or
max can be specified by typing in the desired values and
typing the "return" key.  Note that you can type several
new values without typing a "return."  When you type a
"return," all the new values will be used for
re-displaying the image.

When color composite mode is being used, toggle buttons
allow enabling/disabling the display of each color
component.

To modify the stretch function interactively, click the
left mouse button when the cursor is on the transfer
function plot and hold it down while dragging the cursor.
Note that it is not necessary to click near the transfer
function line.  Also, it is not necessary to stay within
the plot window while dragging.  Up and down movements 
change the slope of the transfer function, which modifies
the contrast of the displayed image.  Left and right
movements change the intercept of the transfer function,
which modifies the overall displayed brightness.  The
image is re-displayed when the mouse button is released.

When the transfer function is modified, the current
function is drawn as bright white.  The two previous
functions are drawn with lower intensity lines.


WRITING AN OUTPUT FILE

The "File" button on the menu bar allows writing an
output file in one of the supported output formats:

    JPEG - A "lossy" compression format.  The user
        can specify the desired quality of the output
        file.  The quality can be in the range 0
        ("terrible") to 100 ("excellent").  Higher
        quality results in larger files.

    TIFF - A lossless file format.  This produces
        files that are larger than JPEG format files.

PROGRAMMER: Jim Torson, U.S.G.S, Flagstaff, AZ