Step Arguments

The resample_spec step has the following optional arguments that control the behavior of the processing and the characteristics of the resampled image.

--pixfrac (float, default=1.0)

The fraction by which input pixels are “shrunk” before being drizzled onto the output image grid, given as a real number between 0 and 1.

--kernel (str, default=’square’)

The form of the kernel function used to distribute flux onto the output image. Available kernels for spectral data are square and point. Other drizzle kernels, available for imaging data, do not conserve spectral flux.

--pixel_scale_ratio (float, default=1.0)

Ratio of input to output spatial pixel scale.

Values greater than 1 indicate that the input pixels have a larger spatial scale, so more output pixels will sample the same input pixel. For example, a value of 2.0 means the output image would have 2 pixels sampling each input spatial pixel. If the input data has units of flux density (MJy/pixel), the output flux per pixel will be half the input flux per pixel. If the input data has units of surface brightness (MJy/sr), the output flux per pixel is not scaled.

Note that this parameter is only applied in the cross-dispersion direction: sampling wavelengths are not affected.

Ignored when pixel_scale or output_wcs are provided.

Note

If this parameter is modified from the default value, the extraction aperture for the extract_1d step must also be modified, since it is specified in pixels.

--pixel_scale (float, default=None)

Absolute pixel scale in arcsec. When provided, overrides pixel_scale_ratio. Ignored when output_wcs is provided.

If the input data has units of flux density (MJy/pixel), the output flux per pixel will be scaled by the ratio of the selected output pixel scale to an average input pixel scale. If the input data has units of surface brightness (MJy/sr), the output flux per pixel is not scaled.

Note that this parameter is only applied in the cross-dispersion direction: sampling wavelengths are not affected.

Note

If this parameter is modified from the default value, the extraction aperture for the extract_1d step must also be modified, since it is specified in pixels.

--output_shape (tuple of int, default=None)

Shape of the image (data array) using “standard” nx first and ny second (opposite to the numpy.ndarray convention - ny first and nx second). This value will be assigned to pixel_shape and array_shape properties of the returned WCS object. When supplied from command line, it should be a comma-separated list of integers nx, ny.

Note

Specifying output_shape is required when the WCS in output_wcs does not have bounding_box property set.

--output_wcs (str, default=’’)

File name of an ASDF file with a GWCS stored under the "wcs" key under the root of the file. The output image size is determined from the bounding box of the WCS (if any). Argument output_shape overrides computed image size and it is required when output WCS does not have bounding_box property set or if pixel_shape or array_shape keys (see below) are not provided.

Additional information may be stored under other keys under the root of the file. Currently, the following keys are recognized:

pixel_area: Indicates average pixel area of the output WCS in units of steradians. When provided, this value will be used for updating photometric quantities PIXAR_SR and PIXAR_A2 of the output image. If pixel_area is not provided, the code will attempt to estimate this value from the WCS.
pixel_shape: dimensions of the output image in the order (nx, ny). Overrides the value of array_shape if provided.
array_shape: shape of the output image in numpy order: (ny, nx).

Note

When output_wcs is specified, WCS-related arguments pixel_scale_ratio and pixel_scale will be ignored.

--fillval (str, default=’NAN’)

The value to assign to output pixels that have zero weight or do not receive any flux from any input pixels during drizzling.

--weight_type (str, default=’ivm’)

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 not exist, the variance is set to 1 for all pixels (equal weighting). If weight_type="exptime", the scaling value will be set equal to the measurement time (TMEASURE) found in the image header if available; if unavailable, the scaling will be set equal to the exposure time (EFFEXPTM).

--single (bool, default=False)

If set to True, resample each input image into a separate output. If False (the default), each input is resampled additively (with weights) to a common output.

--blendheaders (bool, default=True)

Blend metadata from all input images into the resampled output image.

--in_memory (boolean, default=True)

Specifies whether or not to load and create all images that are used during processing into memory. If False, input files are loaded from disk when needed and all intermediate files are stored on disk, rather than in memory.