Set low (or high) intensity or exposure regions of an image to a
constant value.
dmimgthresh infile outfile [expfile] [cut] [value] [verbose] [clobber]
For observations with strongly variable exposure across
an image, you can get spurious results (e.g. with smoothing
or source detection algorithms) where the exposure is very
low. It can therefore be useful to change parts of the
image where the exposure is less than a given value (or
percentage of its maximum value). Equivalently, the same
task may be carried out for maximum values.
The threshold may be expressed as a percentage of maximum or
as an absolute value. The threshold value is compared to the
values in the input exposure map (expfile parameter) and any
pixel whose exposure value is less than threshold is set to a
fixed value (often zero). If an exposure image is not
supplied, the input image itself will be used, allowing you
to threshold an image to alter all pixels above or below a
certain value.
Note that the user-supplied cut value will be truncated to a integer
if the image data is of integer type.
dmimgthresh sky.img new.img expfile=exp.img cut="1.5%"
Zero-out all pixels whose exposure is less than 1.5
percent of the maximum exposure in exp.img. Note that
the default replacement value is 0 (value parameter).
dmimgthresh sky.img new.img expfile=exp.img cut=400.0 value=0.018
Threshold the image, setting all pixels whose exposure
is less than 400 to a value of 0.018.
dmimgthresh sky.img new.img expfile="" cut="20:80" value=0
Set all pixels whose value is less than 20 or greater
than 80 to zero. Since an exposure image is not
provided, the values in sky.img are used for the
thresholding.
dmimgthresh sky.img new.img expfile="" cut=":80%" value=0
Threshold the image, setting all pixels with values
greater than 80% of the peak (of sky.img) to zero.
The output thresholded image.
The exposure image (e.g. an exposure map) used to
determine which pixels are to be changed in the input
image. If an exposure image is provided, it must be
the same size as the data image.
The threshold value; it may be expressed as a percentage of
maximum, e.g., cut="50%", as an actual value, e.g. cut=100.0,
as a min:max value, e.g., "20:80" (set min at 20 counts, max
at 80 counts), or as a min:max percentage, e.g., "20:80%" (set
min at 20%, max at 80%). Both values do not need to be
specified: cut="20:" is the same as cut="20": the minimum
is set at 20 counts; cut=":70%" sets the upper limit to 70%.
Thresholded pixels will be set to this value.
Specifies the level of verbosity in displaying diagnostic messages.
Specifies if an existing output file should be overwritten.
`dmimghist' now supports null value checking. Pixels with the
value NULL are no longer included in the calculations.
Thresholds can now be applied as both lower and upper-limits
using the syntax cut="<min>:<max>".
A value of INDEF creates NaN in the output listing for floating point calculations.
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