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A VIFF input file is the image file format used by KHOROS.  It is comprised
of a header that contains all of the necessary information about the image
file, followed by the data.  A VIFF file may be broken down into 
an IMPLICIT or EXPLICIT file.  An IMPLICIT file contains Y data, with the
location information (ie. X axis) implied from the data itself.  An EXPLICIT
file contains the data as well as the specific location information.  A more
detailed description of IMPLICIT and EXPLICIT files and their use is
provided below. Xprism2 is capable of handling all VIFF image data storage
formats except BIT, and is capable of handling multiband images. 
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Input of IMPLICIT Image Files
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In the course of image processing, the user may want to plot a
single column or a single row of pixel values; this can be done using
the 2D plot capability of xprism2.  In preparation for this operation,
a image or sub-image consisting of a single row or column must be
created before beginning the session with xprism2 (see man pages on vextract).
Alternatively, the user may wish to create a 2D plot of a typical image or
subimage that is square or rectangular.
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To accomodate the possibilities in each case, each of these three
categories of images are acceptable for plotting in 2D.
The image used may have 1 row, 1 column, or a variable number
of rows and columns. If, however, the attempt is made to plot an
image with 0 rows or  0 columns, xprism2 will print an error message,
as this implies insufficient data to create any sort of plot.
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If the column size of the image is 1 (i.e., the image consists of a single 
row), xprism2 will create a 2D plot where the X Axis represents the index 
of each pixel in the row, and the Y Axis represents the value of each pixel.
Similarly, if the row size of the image is 1 (i.e., the image consists
of a single column), xprism2 will create a 2D plot where the X Axis
represents the index of each pixel in the column, and again, the Y Axis
represents the value of each pixel.
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When a "normal" image is plotted in two dimensions, (that is, an image
with more than one row and more than one column) the following procedure
is utilized by xprism2 to create the 2D plot.
Each scanline of data of the image, from top to bottom, is interpreted as
contiguous plot data; scanlines of pixels are plotted end to end as a single
series of points.  Thus, when viewing a square or rectangular image as a
2D plot, the X axis includes all rows and columns of image data, while
the Y axis represents the pixel values at each pixel position.
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To plot an Implicit Image File, fill in the "Filename" parameter box with the
desired filename (for more information, see the help on the Environment Pane),
and click on the "PLOT FILE" action button.  The implicit image file
will be read in, interpreted as described above,  and displayed according 
to the current value of the "plot type" toggle.
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Input of EXPLICIT Image Files
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Explicit Image Files may also be used as input to xprism2; in this case,
the X and Y data is explicitly stated, so there is no interpretation
to be done as is the case with an Implicit Image file.  The X coordinates come
directly from the location data; the Y coordinates come from the image data.
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Saving a plot as an Explicit Image File (see help on the "Files" pane on the
"Output" subform) implies that it can be exactly reproduced whenever it is 
used as input to xprism2, since the data points are saved explicitly.  
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Note, however, that plot attributes such as labels, colors, fonts, line types,
etc. cannot be saved in either Implicit or Explicit Image File Format, 
as these attributes have no storage place in an image file.  
Any time a plot is saved as an image and later re-displayed, any of these 
attributes will have to be re-set to the desired values.
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To plot an Explicit Image File, fill in the "Filename" parameter box with the
desired filename (for more information, see the help on the Environment Pane),
and click on the "PLOT FILE" action button.  The explicit image file
will be read in and displayed according to the current value of the 
"plot type" toggle. 
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The number of points to be displayed in the workspace may be controlled by
changing the "step size", "begin" and "end" data points.  Note that this
does not change the data in the file, but only how the data is displayed
in the workspace. 
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Multiband and Complex Data Images
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Xprism2 is capable of handleing multiband VIFF images and images of all
data types except BIT. When a multiband VIFF image is read in, a list
of bands will pop up. The user must select the desired band to plot. To
plot more than one band, one must read the image in again and select the
desired band. When a VIFF image has a data storage type of COMPLEX, a
list asking which complex type to plot pops up. The user must select the
desired complex plot type. Currently one can choose to plot the Real part,
the Imaginary part, the Magnitude or the Phase. Xprism2 uses lvctor to
convert the complex type. For more information in this conversion process
see vctor(1) or lvctor(3).
