- Form: IMPOST imbuf [BOX=b] [Z=zero] [L=span] [CLIP]
[POSITIVE] [TITLE]
-
- [HIST=xxx] [LAND] [FOUR] [AXES] [COMMENT] [COMMENT=xxx]
[FILE=xxx] [OUT=xxx]
-
- [SCALE=s] [CEN=r,c] [FLIP] [BAR=xxx] [NOBAR] [WIND=w,h]
[ORIGIN=x,y] [PAGE=L,S]
-
- [COPIES=n] [LARGE] [INFO] [INT] [MACRO=]
-
- imbuf
- The buffer containing the image to be printed.
- BOX=b
- Only print the region within the given box.
- Z=zero
- Zero point of the intensity mapping.
- L=span
- Span of the intensity mapping.
- CLIP
- Prevent roll-over of the intensity mapping.
- POSITIVE
- Print the image intensities as White-on-Black.
The default mapping is Black-on-White.
- TITLE
- Write the OBJECT name on the print (from the header).
- HIST
- Map image intensities using flat histogram equalization.
- HIST=xxx
- Map image intensities using other histogram scalings
Options: (FLAT,SQRT,LOG). "HIST" = "HIST=FLAT"
- LAND
- Output will appear in LANDSCAPE mode
- FOUR
- Use a 4 bit (16 level) gray scale rather than the
default 8 bit (256 level) gray scale.
- AXES
- Draw coordinates axes around the image.
- COMMENT='xxx'
- Add a comment line to the print. Comments may be
up to 64 characters long.
- COMMENT
- Prompt the user interactively for the comment line.
- FILE=psfile
- Direct the output into a file named "psfile".
- OUT=psfile
- (same as FILE=psfile)
- SCALE=s
- specify the pixel scale in units/pixel.
- CEN=(r,c)
- specify the image fiducial center in pixels for
scaled coordinate axes (see SCALE=).
- FLIP
- flips image in rows (bottom-to-top raster order).
- BAR='xxx'
- Label the gray scale intensity bar with the string
given. Default bar label is "Intensity"
- NOBAR
- Do not draw a gray scale intensity bar on the print.
- INFO
- Write in a line of auxiliary info on the print.
- INT
- Puts user into interactive Mongo mode for labelling.
- MACRO=macrofile
- Executes Mongo macro file macrofile after drawing
- Advanced Page Control
-
- COPIES=n
- Specify the number of copies to print if more than 1.
- WIND=(w,h)
- Specify the maximum size in inches of the window in
which IMPOST will try to print the image.
- LARGE
- Alternative to WIND=, will make the window as large as
possible for the given paper size and orientation.
- ORIGIN=(x,y)
- Specify the origin of the plotting window in inches
from the lower left-hand corner of the paper.
- PAGE=(L,S)
- specify the physical size of the paper in inches.
"L" = long dimension, "S" = short dimension.
IMPOST makes a hardcopy print of an image in PostScript format. It
is designed to be used just like the TV command, with very similar
keywords. You can include extra information on the picture with the
TITLE, AXES, COMMENT, INFO and related keywords. These are discussed
below.
IMPOST creates a PostScript file on disk. This file will be located in the
current directory (either where you started VISTA or under Unix versions of
VISTA, the last directory you CD'd to). By default this file will take the
name "image.ps". You can specify your own name for the file by using the
FILE= or OUT= keywords. Currently, this file is not automatically printed.
From outside of VISTA (or from a spawned subprocess or C-shell), submit
this to your printer as you would submit any other PostScript file (e.g.,:
"lpr image.ps" on a Unix system, or "$ print/queue=pslaser image.ps" on a
VMS system).
Multiple copies can be made using the COPIES=n keyword. The POSITIVE
keyword makes white images on a black background; the default is to make
black images on a white background.
Output from IMPOST, if prepared with care, is of the highest quality.
IMPOST generated prints made on good quality paper or special "stat" paper
have been accepted for publication without re-photography required.
Intensity Scaling
IMPOST produces a hardcopy of an image by representing pixel intensities as
an 8-bit halftone gray scale. The optional keyword "FOUR" will use a 4-bit
(16-level) gray scale instead. Although an 8-bit gray scale has 256 levels
from white to black, on standard 300 dpi laser printers, only 32 levels are
distinguishable. The output is a PostScript file which may be sent to any
standard PostScript hardcopy device.
The simplest intensity scaling is through use of the Z= and L= keywords
like in the TV command. These set the zero point (Z=ZERO) and intensity
span (L=SPAN) of a "linear" mapping from the actual image intensity in each
pixel, IMG(r,c), to a displayed gray scale value between 0 and 255,
INTENS(r,c), following the formula:
- INTENS(r,c) = [IMG(r,c) - ZERO]*(255/SPAN)
With the FOUR option, the scale factor is 15 instead of 255, and
INTENS(r,c) will take values from 0 to 15.
In this simple linear mapping, pixels with IMG(r,c) <= ZERO will set
INTENS(r,c)=0 (white) and pixels with IMG(r,c)=ZERO+SPAN will set
INTENS(r,c)=255 (black). If the CLIP keyword is used, then all values of
IMG > ZERO+SPAN are set black, otherwise, the color scale "wraps" and above
IMG=ZERO+SPAN, INTENS starts again at 0. This continues modulo (255/SPAN)
until all pixel intensity values are mapped.
The default mapping is an inverse (or "negative") scale, where the image is
drawn as black against a white background. If the optional keyword
POSITIVE is given, then the intensities are mapped in a more "normal" or
"positive" scale in which the image is displayed as white against a black
background, though the results with most laser printers is less than
optimal.
The second scaling option is to map image intensities into an 8-bit gray
scale using the distribution of pixel intensities in the image to provide a
scaling in which all gray levels are equally present. Such a scaling is
called a "Histogram Equalization", and is used to bring up faint features
without sacrificing more high-intensity features in the same image. This
is done using the HIST keyword. Histogram equalization is a common
technique in image processing, most notably it is used for making the
high-contrast images that came from the Voyager and Viking space probes.
Note that a simple one-to-one mapping of pixel intensities and gray level
is lost, and such mapping should be used with caution.
If the Z= and L= keywords are used with HIST, then Z= is taken to be the
lowest intensity value to be considered, and L= tells hist to ignore all
intensities above Z+L when determining the histogram mapping. The CLIP
keyword is implicit with any histogram scaling option - no rollover is
permitted.
Additional histogram scaling options are available via the HIST=LOG and
HIST=SQRT keywords. HIST=LOG will map intensities by equalizing over
logarithmic intervals. This is useful when there is a very large range of
intensities in the image, and you wish to emphasize the brighter regions
without washing out fainter features. The HIST=SQRT option will map
intensities by equalizing over square-root intervals. This represents a
middle ground between the "FLAT" histogram mapping described above (which
enhances fainter regions) and the "LOG" histogram mapping.
Some experimentation to determine the best option to use will undoubtably
be required. Images which are mostly background sky will usually not
benefit from any form of histogram equalization, while images of extended
objects in which the frame is more-or-less filled with "object" will
usually benefit. By setting the zero point (Z=) to be above the image sky
level, you can have the advantages of the histogram equalization scalings
while still showing surrounding objects.
Labeling the Output
By default, IMPOST will only draw a box around the image and display a bar
with the gray scale intensity range (0-255 or 0-15) in a box below the
image. You can add axes and labels using a variety of keywords provided.
- TITLE
- puts the object name of the image (stored in the header in
the OBJECT FITS card). The title appears above the upper
left-hand corner of the image in large type. Standard
Mongo escape sequences can be used to print special characters
(like a greek alpha), or super- and sub-scripts.
- COMMENT
- appends a line of text below the image title in a slightly
smaller font. Comments may be specified on the command line
by using the COMMENT='comment string' keyword. You may also
have IMPOST prompt the terminal for the comment by using
the COMMENT keyword without an ='s sign. Comments may be
single or multiple words up to 64 characters long. Note that
Mongo special characters may also be used, in addition to
super- and sub-scripts, but the extra escape sequence characters
count against the 64 maximum.
- AXES
- In its simplest form, AXES will draw coordinate axes around
the image and label the axes in pixel units. Using the
SCALE= and/or CEN= keywords (see below) will allow you
to scale the axes in arcseconds.
- SCALE=
- Sets the pixel scale in arcseconds/pixel for the AXES
keyword (above). When used with AXES, the center of
the image is taken to be the origin (0,0), and the axes
are labeled accordingly. To set a particular pixel to be
the center, use the CEN= keyword.
- CEN=
- Sets the origin of the image to be the (r,c) location given.
Two (2) arguments must be given, and need not lie inside the
region actually plotted (useful if you wish to show a zoom of
a region in a larger image while still preserving the original
coordinate system). If CEN is not used with SCALE, then the
center of the region displayed is assumed to be the origin.
(r,c) may be fractional pixel locations (say the centroid of
a galaxy or planetary nebula central star).
- NOBAR
- Tells IMPOST not to draw in the gray intensity scale bar
on the image.
- BAR=
- By default, IMPOST will label the gray intensity scale
bar with the word "Intensity", but you may set it to
anything you like with the BAR= keyword. For example,
BAR='Log H
ga Flux' will label the intensity bar as
indicating the logarithm of the H-alpha flux. Any valid
Mongo special character escape sequence (including
super- and sub-scripts is allowed).
- INFO
- Puts a line of auxiliary information across the bottom of
the print. This provides a hardcopy of the parameters
that went into the picture (zero point, span, clipping, etc).
- INT
- Puts the user into interactive Mongo after drawing image. The
limits are the row and column limits. Here you can do your
own labelling, overlays of contours, etc.
- MACRO=file
- Executes the Mongo macro file after drawing image. Like
INT but uses predefined Mongo macro.
- FLIP
- This keyword "flips" the image orientation in the window
vertically (about rows) so that the origin of the image is
in the lower left-hand corner of the page rather than the
upper left-hand corner as is default for VISTA. This is
the orientation used by IRAF and STSDAS.
Advanced Page Control
A number of optional keywords are provided which affect the physical size
of the image as it appears on the page, its orientation, the number of
copies printed etc. These options may be used if IMPOST prints are
intended for use in papers or dissertations, where precise specification of
margins and the location and orientation of the image on the page are
essential. These keywords are described below:
- LAND
- This keyword will cause the print to be oriented with the
horizontal axis aligned with the long side of the paper
(so-called "landscape" mode). By default, IMPOST prints are
made in "portrait" mode.
- COPIES=n
- If more than one copy is desired, then set the COPIES keyword.
This option is very economical of processing time, as the
printer only has to "draw" the image once and then knock off
as many copies as required. This is far more efficient than
printing the same file N-times.
- WIND=(w,h)
- This keyword specifies the maximum possible size of the
plotting window, in inches. The window is the largest
region in which IMPOST will try to fit the image.
By default, the plotting window is:
Portrait (default): 6" x 6"
Landscape (LAND): 8" x 5"
Dimensions are specified as "width","height" in units of inches.
These dimensions must be smaller than the paper dimensions
(see PAGE keyword).
- LARGE
- An alternative to WIND= is the "LARGE" keyword. Will attempt
to make the window as large as possible on the page, leaving only
a 0.25-inch margin around the edge. LARGE is equivalent to
ORIGIN=0.25,0.25 WIND=8.0,10.5 PAGE=11.0,8.5
- ORIGIN=(dh,dv)
- Specifies the origin of the plotting window
in inches measured from the lower left-hand corner of the
paper. DH is the horizontal offset, and DV is the vertical
offset. By default, IMPOST tries to center the plotting
window on the page, and adds a 30pt "binding margin" to
Portrait mode prints. ORIGIN overrides this binding margin.
- PAGE=(lng,sh)
- This keyword specifies the physical size of the paper in
inches. "lng" = long dimension, "sh" = short dimension.
Note that which is horizontal or vertical depends on
whether or not the LAND keyword was used. For example,
PAGE=(11,8.5) is equivalent to the IMPOST default, and
corresponds to the dimensions of standard U.S. letter
paper. PAGE should only be used if you have non-standard
sized paper in your local PostScript printer and do not
wish to change the hardcoded values in the IMPOST fortran
code itself. European VISTA users should have their
local custodians hardwire IMPOST to the appropriate local
paper size.
Advanced Notes:
IMPOST uses the LickMongo PostScript drivers to make the axes and labels.
As such, while PostScript instructions generated by this program may be
used to produce the image hardcopy on any PostScript device via an
appropriate server, they do not fully conform to to the "Encapsulated
PostScript" structuring conventions described in the 'PostScript Language
Program Design' Manual (Adobe Systems Incorporated 1988), or following the
Version 2.0 EPS Specifications (Adobe Systems Inc. January 1989). In
future releases of LickMongo, this should be corrected (it is an artifact
of the fact that the LickMongo PostScript drivers were written well before
the standards were published). Even so, with minor modifications, it
should be possible to import images created with IMPOST into other
encapsulated PostScript files (like those generated by TeX).
Images created with IMPOST have been displayed successfully on the X11/NeWS
window system, on displayed PostScript devices, and transmitted
electronically via both email and tcp/ip with no difficulties.
'PostScript' is a registered trademark of Adobe Systems Incorporated.
A Note About the Name:
IMPOST is the command formerly known as POSTIT until 1997 Nov 21, when the
author (Rick Pogge) was made aware of a letter to his department chairman
from the law firm of Arnold, White, & Durkee. This firm represents the
Minnesota Mining & Manufacturing Company (3M) in trademark and other
intellectual property rights matters. It seems after coming across a web
version of the Prospero manual (a VISTA derivative written at OSU that
incorporates POSTIT because it was written by Rick Pogge), they deemed our
use of the word POSTIT as an infringment of the trademark of 3M for its
famous yellow sticky notes, aka Post-It(tm) Notes that might potentially
confuse people encountering the web version of our help pages.
While we disagree that anyone could possibly confuse the ubquitous yellow
sticky notes manufactured by 3M with an obscure function embedded within an
even more obscure advanced astronomical image processing package, the
current legal climate of excessive litigiousness that serves only to
trivialize intellectual property rights requires that we change the name.