Plotting FITS images
This page gives a brief overview of how to make basic plots of FITS files.
Table of contents
Basic sky plot
The simplest plotting command is
everystamp plot --image <fits image>
This will create a simple RA-DEC sky plot of the provided image using a linear stretch.
Image manipulation
EveryStamp offers image manipulation that can be used to visualise an image to your liking. The options outlined below are applied in the following order, if used:
- HDR tonemapping
- CLAHE
- Gamma correction
Image stretching and colour maps
The --stretch
parameter can be used to apply log, sqrt, squared, asinh or sinh stretches to the image. The colour map and its limits can be controlled via --cmap
, --cmap-min
and --cmap-max
. N.B. the latter values apply to post-stretched values.
Gamma correction
Gamma correction can be applied as a final step by adding --gamma <gamma>
to the plotting arguments. As implemented here, this will gamma stretch an image by
A value of \(\gamma = 2\) results in a square root stretch of the input image.
Contrast limited adaptive histogram equalisation
Contrast limited adaptive histogram equalisation (CLAHE) tries to improve contrast in the image by applying a local histogram equalisation while simultaneously limiting the contrast enhancement in an attempt to reduce the amplification of noise. It is applied as a second-to-last step, before any gamma correction, and can be enabled by using --CLAHE
. The --CLAHE-gridsize
and --CLAHE-cliplim
control the size of the local region and the amount of contrast enhancement, respectively.
HDR tonemapping
When dealing with a high dynamic range (HDR) image, simple tonemapping operators may not be enough. If LuminanceHDR is installed (see installation), several HDR tonemapping algorithms are available through the --hdr-tonemap
argument.
Overplotting contours
If you have an image you’d like to overplot as contours, it can be passed to --contour_image
.
Plotting styles
The --style
option controls in what style an image is plotted. Currently, the only available alternative style is that of the SRTPLOT task by Hogbom 1974.
SRTPLOT
SRTPLOT style plots draw slices of intensity along the right ascension axis every number of (pixel) steps in declination, offset by some value. To enable this style, use --style srtplot
. The settings --srt_lines
and --srt_offset
control how many declinations are plotted and what the vertical offset between each slice is on the plot.