xdisplay (Aug2004) |
rjtools
|
xdisplay (Aug2004) |
xdisplay
xdisplay - flexible task to display an image with sensible defaults
xdisplay image [buff] [z1] [z2] [lsig] [hsig] [zmode] [cenx] [ceny]
[sizx] [sizy] [zoom] [erase] [verbose]
- image = ""
- Image to display
- buff = 1
- Frame buffer to use for display
- z1 = INDEF
- Fix minimum level to display to 'z1', unless 'z1' is smaller than
the minimum pixel value
- z2 = INDEF
- Fix maximum level to display to 'z2', unless 'z2' is larger than
the maximum pixel value
- lsig = 3.
- Set minimum level to display to 'lsig' sigma below the background
level, unless that would be smaller than the minimum pixel value
- hsig = 15.
- Set maximum level to display to 'hsig' sigma above the background
level, unless that would be larger than the maximum pixel value
- zmode = "linear" ["linear"|"log"]
- Type of transformation to apply
- cenx = 0.5
- X center position (fraction of the full image display)
- ceny = 0.5
- Y center position (fraction of the full image display)
- sizx = 1.0
- Display window horizontal size
- sizy = 1.0
- Display window vertical size
- zoom = 1.
- Default magnification factor
- erase = yes
- Erase frame before loading image?
- verbose = no
- Print warnings and messages?
- (tz1) [real]
- Minimum level actually displayed (after sigma clipping and fuzzy logic)
- (tz2) [real]
- Maximum level actually displayed (after sigma clipping and fuzzy logic)
- (tsig) [real]
- Approximate standard deviation after clipping
- (tmax) [real]
- Maximum pixel value found after clipping in a section with the same
center as the full region to display, but 1/4 the size.
- (tmin) [real]
- Minimum pixel value found after clipping in a section with the same
center as the full region to display, but 1/4 the size.
User interface/wrapper around task 'display', providing a somewhat
better default estimate of the scale, contrast and range of levels to
display, particularly in the case of images of extended objects. But
even for stellar images, by increasing the default values of 'lsig' and
'hsig' (e.g., 5. and >=25.), good results are obtained.
Parameters 'lsig' and 'hsig' define sigma clipping levels that are
applied after an initial iteration to determine the image statistics.
The resulting range of pixel values is compared to the values specified
for 'z1' and/or 'z2' (if they differ from INDEF), and are then further
tweaked based on the statistics in a smaller region 1/4 the size
centered on the region that is to be displayed. The rationale for this
is that usually the object(s) of interest are nearer to the center than
to the border of the display region.
This task is mainly used as a 'quick-look' tool. For a large variety of
data (be they spectra, biases, stellar images or images of extended
objects; at very low [HST UV] or very high [groundbased NIR] signal
levels; and with very small or very large dynamic range) this task will
display your image such that you actually see you object or feature of
interest; once sensible display limits/contrast are determined, native
IRAF task 'display' is of course much faster. 'display' also allows you
to specify limits that significantly exceed the actual range of pixel
values (which this task does not).
Display an image in the default frame buffer:
rj> unlearn xdispl
rj> xdispl N3795B.fits verbose+
Displaying image "N3795B.fits": z1=53.20, z2=261.23
rj> xdispl N3795B.fits z1=INDEF z2=INDEF zmode="log" verbose+
Displaying image "N3795B.fits": z1=53.20, z2=261.23
rj> xdispl N3795B.fits z1=-1000 z2=1000 zmode="log" verbose+
WARNING: z2 > IMAX = 286.1349! Ignoring requested 'z2'...
WARNING: z1 < IMIN = 50.38003! Ignoring requested 'z1'...
Displaying image "N3795B.fits": z1=50.38, z2=286.13
rj> xdispl N3795B.fits z1=-1000 z2=1000 lsig=5. hsig=20. verbose+
WARNING: z2 > IMAX = 363.2227! Ignoring requested 'z2'...
WARNING: z1 < IMIN = 12.86221! Ignoring requested 'z1'...
Displaying image "N3795B.fits": z1=12.86, z2=363.22
rj> unlearn xdispl
rj> xdispl N3795B.fits lsig=5. hsig=20. verbose+
Displaying image "N3795B.fits": z1=25.18, z2=338.95
imstatistics, imgstat, chkimg, rpparse, rpbuild