SkyImage¶
- class jwst.skymatch.skyimage.SkyImage(image, wcs_fwd, wcs_inv, pix_area=1.0, convf=1.0, mask=None, id=None, skystat=None, stepsize=None, meta=None, reduce_memory_usage=True)[source]
Bases:
object
Container that holds information about properties of a single image such as:
image data;
WCS of the chip image;
bounding spherical polygon;
id;
pixel area;
sky background value;
sky statistics parameters;
mask associated image data indicating “good” (1) data.
Initializes the SkyImage object.
- Parameters:
image (numpy.ndarray, NDArrayDataAccessor) – A 2D array of image data or a
NDArrayDataAccessor
.wcs_fwd (function) – “forward” pixel-to-world transformation function.
wcs_inv (function) – “inverse” world-to-pixel transformation function.
pix_area (float, optional) – Average pixel’s sky area.
convf (float, optional) –
Conversion factor that when multiplied to
image
data converts the data to “uniform” (across multiple images) surface brightness units.Note
The functionality to support this conversion is not yet implemented and at this moment
convf
is ignored.mask (numpy.ndarray, NDArrayDataAccessor) – A 2D array or
NDArrayDataAccessor
of a 2D array that indicates which pixels in the inputimage
should be used for sky computations (1
) and which pixels should not be used for sky computations (0
).id (anything) – The value of this parameter is simple stored within the
SkyImage
object. While it can be of any type, it is preferable thatid
be of a type with nice string representation.skystat (callable, None, optional) –
A callable object that takes a either a 2D image (2D
numpy.ndarray
) or a list of pixel values (a Nx1 array) and returns a tuple of two values: some statistics (e.g., mean, median, etc.) and number of pixels/values from the input image used in computing that statistics.When
skystat
is not set,SkyImage
will useSkyStats
object to perform sky statistics on image data.stepsize (int, None, optional) – Spacing between vertices of the image’s bounding polygon. Default value of
None
creates bounding polygons with four vertices corresponding to the corners of the image.meta (dict, None, optional) – A dictionary of various items to be stored within the
SkyImage
object.reduce_memory_usage (bool, optional) – Indicates whether to attempt to minimize memory usage by attaching input
image
and/ormask
numpy.ndarray
arrays to file-mapped accessor. This has no effect when input parametersimage
and/ormask
are already ofNDArrayDataAccessor
objects.
Attributes Summary
Set or get
SkyImage
'sid
.Set or get
SkyImage
'simage
data array.Get
SkyImage
'simage
data shape.Indicates whether sky value was successfully computed.
Set or get
SkyImage
'smask
data array orNone
.Set or get mean pixel area.
Get bounding polygon area in srad units.
Get image's bounding polygon.
Get RA and DEC of the vertices of the bounding polygon as a
ndarray
of shape (N, 2) where N is the number of vertices + 1.Sky background value.
Stores/retrieves a callable object that takes a either a 2D image (2D
numpy.ndarray
) or a list of pixel values (a Nx1 array) and returns a tuple of two values: some statistics (e.g., mean, median, etc.) and number of pixels/values from the input image used in computing that statistics.Methods Summary
calc_bounding_polygon
([stepsize])Compute image's bounding polygon.
calc_sky
([overlap, delta])Compute sky background value.
copy
()Return a shallow copy of the
SkyImage
object.intersection
(skyimage)Compute intersection of this
SkyImage
object and anotherSkyImage
,SkyGroup
, orSphericalPolygon
object.set_builtin_skystat
([skystat, lower, upper, ...])Replace already set
skystat
with a "built-in" version of a statistics callable object used to measure sky background.Attributes Documentation
- id¶
Set or get
SkyImage
’sid
.While
id
can be of any type, it is preferable thatid
be of a type with nice string representation.
- image¶
Set or get
SkyImage
’simage
data array.
- image_shape¶
Get
SkyImage
’simage
data shape.
- is_sky_valid¶
Indicates whether sky value was successfully computed. Must be set externally.
- pix_area¶
Set or get mean pixel area.
- poly_area¶
Get bounding polygon area in srad units.
- polygon¶
Get image’s bounding polygon.
- radec¶
Get RA and DEC of the vertices of the bounding polygon as a
ndarray
of shape (N, 2) where N is the number of vertices + 1.
- skystat¶
Stores/retrieves a callable object that takes a either a 2D image (2D
numpy.ndarray
) or a list of pixel values (a Nx1 array) and returns a tuple of two values: some statistics (e.g., mean, median, etc.) and number of pixels/values from the input image used in computing that statistics.When
skystat
is not set,SkyImage
will useSkyStats
object to perform sky statistics on image data.
Methods Documentation
- calc_sky(overlap=None, delta=True)[source]¶
Compute sky background value.
- Parameters:
overlap (SkyImage, SkyGroup, SphericalPolygon, list of tuples, None, optional) – Another
SkyImage
,SkyGroup
,spherical_geometry.polygons.SphericalPolygon
, or a list of tuples of (RA, DEC) of vertices of a spherical polygon. This parameter is used to indicate that sky statistics should computed only in the region of intersection of this image with the polygon indicated byoverlap
. Whenoverlap
isNone
, sky statistics will be computed over the entire image.delta (bool, optional) – Should this function return absolute sky value or the difference between the computed value and the value of the sky stored in the
sky
property.
- Returns:
skyval (float, None) – Computed sky value (absolute or relative to the
sky
attribute). If there are no valid data to perform this computations (e.g., because this image does not overlap with the image indicated byoverlap
),skyval
will be set toNone
.npix (int) – Number of pixels used to compute sky statistics.
polyarea (float) – Area (in srad) of the polygon that bounds data used to compute sky statistics.
- intersection(skyimage)[source]¶
Compute intersection of this
SkyImage
object and anotherSkyImage
,SkyGroup
, orSphericalPolygon
object.- Parameters:
skyimage (SkyImage, SkyGroup, SphericalPolygon) – Another object that should be intersected with this
SkyImage
.- Returns:
polygon – A
SphericalPolygon
that is the intersection of thisSkyImage
andskyimage
.- Return type:
SphericalPolygon