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Add description of calculation of VAR_SKY.
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mairanteodoro committed Dec 30, 2024
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14 changes: 10 additions & 4 deletions docs/roman/resample/arguments.rst
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Expand Up @@ -77,14 +77,20 @@ image.
The weighting type for each input image.
If `weight_type=ivm` (the default), the scaling value
will be determined per-pixel using the inverse of the read noise
(VAR_RNOISE) array stored in each input image. If the VAR_RNOISE array does
(``VAR_RNOISE``) array stored in each input image. If the ``VAR_RNOISE`` array does
not exist, the weight is set to 1 for all pixels (equal weighting).
If `weight_type=exptime`, the scaling value will be set equal to the
exposure time found in the image header.
If `weight_type=ivsky`, the scaling value will be determined per-pixel
using the inverse of the sky variance (VAR_SKY) array calculated in the
resample step for each input image. If the VAR_SKY array does
not exist, the weight is set to 1 for all pixels (equal weighting).
using the inverse of the sky variance (``VAR_SKY``) array calculated in the
resample step for each input image. ``VAR_SKY`` is given by the following equation:

.. math::
\text{VAR\_SKY} = \text{VAR\_RNOISE} + \text{VAR\_POISSON} \, \frac{ med(\text{DATA}) }{ \text{DATA} },
where :math:`\text{DATA}` and :math:`med(\text{DATA})` correspond to the data array and its median, respectively.
If the ``VAR_SKY`` array does not exist, the weight is set to 1 for all pixels (equal weighting).

``--single`` (bool, default=False)
If set to `True`, resample each input image into a separate output. If
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