mktracer -- create a trace image from NIRSPEC low-dispersion flat
mktracer input output
Name of input image. This image should be a flat image taken
with NIRSPEC in low-dispersion mode.
Name of output image. This image should contain two lines
available for tracing.
The mktracer task will take as input a NIRSPEC
low-dispersion flat and generate an image which can be used to map and
remove the x distortions from accompanying NIRSPEC
images. The following manipulations are performed on the input
image in order to generate the output image:
an 11×11 pixel boxcar filter is passed over the image
to eliminate small-scale features such as hot pixels and
grunge on the slit, while still maintaining the large-scale
features of the image
a gradient filter is used to locate places where the flux
changes along each image row
the temporary image is renormalized to a maximum value of 1
the temporary image is squared to make both the up and down
slopes of the illuminated region be positive, and also to
reduce the width of the gradient peaks for easier detection
an 11×1 median filter is passed over the image to
smooth over insignificant peaks in each row
the temporary image is convolved with a wide Gaussian
filter in the x direction in order to merge double
peaks into single ones
All operations take place on temporary images in the current
directory. The input image is not affected by these operations.
The output image is suitable as input to the task xdistcor.
Given an image 24des0057.fits which is a NIRSPEC
low-dispersion flat, produce a trace image called
mktracer mktracer 24des0057 trace
Several temporary images will be created and deleted in the
current working directory.