Summary:
- To Load an Image into the Image Display Buffer (Frame):
- Click on the Images Pull-down Menu and select Load
Image. Type the pathname of the file containing the image data in
the SAOtngDialog window which appears, or
- Double-click on the desired filename in the File Listing
section of the XDir directory browser.
- To display a different part of the image, select the desired Image
Quadrant from the Region Pull-down Menu, and then select
Redisplay Current Image from the same menu.
- To display multiple images:
- Select a new frame from the appropriate item in the Frame
Pull-down menu or NxtFram/PrvFram command buttons, and load desired image.
Contents of This Section
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SAOtng can display image data stored in IRAF image format, IRAF QPOE
format, standard FITS image format, or raw data arrays. The file types
generally are recognized on the basis of their file extensions (.imh
for IRAF images, .qp for QPOE, and .fit or .fits for FITS). Users who
wish to input images in other formats can do so provided those data
can be converted to FITS image format, as discussed in SAOtng Advanced Topics.
When an image file name is sent to SAOtng, a check is made to see
if the file is a FITS file (regardless of extension). If it is, then
the file is loaded directly. Otherwise, SAOtng checks its extension
list to see if the file contains a recognized image file extension.
If so, the appropriate image access programs are run to extract the
desired image section for display. If the file does not contain an
image extension, SAOtng checks for an
array specification and loads the file as an array if possible.
If a pathname is not given for the specified image file, SAOtng will
search each directory in the user's path. This implies that if
commonly-used data directories are added to the search path, then the
images contained in these directories can be loaded without having to
specify the full path. SAOtng also will expand environment
variables when processing file names.
SAOtng displays data in a 512x512 pixel image buffer or frame. By default,
this frame is filled with data from an image section centered in
the input image file. The actual dimensions, D, of the image section are
determined by the input blocking factor, B, such that D = Bx512. For
example, for a 4096x4096 image at B=2, the displayed image section
will be centered at 2048,2048 with dimensions 1024x1024. The details
of the displayed image section are listed below the color bar in the
SAOtng display. The input blocking factor may be selected from the
Region Pull-down Menu.
By default, the origin of the image display buffer (i.e., display
pixel 0,0) is located in the lower left of the image display (standard
IRAF convention). Relocating the display origin
may be accomplished by selecting Flip Image By X &/or Y from the
Zoom Pull-down Menu. N.B. SAOtng labels pixels starting
with 0. This is different from the IRAF/FITS convention, which labels
pixels starting with 1.
In addition to an image section at the center of the input image,
SAOtng can display sections centered at the four quadrants, by
selecting the appropriate section (e.g. Upper Right of Image)
from the Images/Set Section To Load Pull-down Menu, and then
selecting Redisplay Current Image from the Imagesmenu.
For example, in a 2048x2048 image at a blocking factor of 1, selecting
Upper Right of Image will display a 512x512 image section
centered at 1536,1536. By changing the blocking factor, larger image
sections centered at this location can be displayed. SAOtng does not
yet have the ability to display image sections centered at arbitrary
locations.
SAOtng provides two mechanisms for displaying multiple images.
By selecting the appropriate frame section (e.g. Upper Right of
Frame) from the Region Pull-down Menu, the user may display
different image data in each of the four frame quadrants. However, the
same color map, scaling function, and zoom apply to all frame
quadrants.
The user may also display different image data in different frames. In
this case, each frame may have a different color map, scaling, and
zoom. Alternate frames may be selected by choosing the appropriate
item (e.g. Go To Frame 2) from the Frame Pull-down Menu
or by using the NxtFram/PrvFram command buttons. By default,
SAOtng allocates space for 2 frames, but additional frames may be
created by selecting Create New Frame in the Frame menu.
SAOtng will blink frames (i.e., repeatedly display all frames in rapid
succession) if the Blink Frames item in the
Frame menu is selected.
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Last Updated May 1, 1995