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# Reference/API

## astropy.nddata Package

The `astropy.nddata` subpackage provides the `NDData` class and related tools to manage n-dimensional array-based data (e.g. CCD images, IFU Data, grid-based simulation data, …). This is more than just `numpy.ndarray` objects, because it provides metadata that cannot be easily provided by a single array.

### Functions

`add_array`(array_large, array_small, position, *) | Add a smaller array at a given position in a larger array.
`bitfield_to_boolean_mask`(bitfield[, ...]) | Converts an array of bit fields to a boolean (or integer) mask array according to a bit mask constructed from the supplied bit flags (see `ignore_flags` parameter).
`block_reduce`(data, block_size[, func]) | Downsample a data array by applying a function to local blocks.
`block_replicate`(data, block_size[, conserve_sum]) | Upsample a data array by block replication.
`extend_bit_flag_map`(cls_name[, base_cls]) | A convenience function for creating bit flags maps by subclassing an existing map and adding additional flags supplied as keyword arguments.
`extract_array`(array_large, shape, position) | Extract a smaller array of the given shape and position from a larger array.
`fits_ccddata_reader`(filename[, hdu, unit, ...]) | Generate a CCDData object from a FITS file.
`fits_ccddata_writer`(ccd_data, filename[, ...]) | Write CCDData object to FITS file.
`interpret_bit_flags`(bit_flags[, flip_bits, ...]) | Converts input bit flags to a single integer value (bit mask) or `None`.
`overlap_slices`(large_array_shape, ...[, ...]) | Get slices for the overlapping part of a small and a large array.
`reshape_as_blocks`(data, block_size) | Reshape a data array into blocks.
`subpixel_indices`(position, subsampling) | Convert decimal points to indices, given a subsampling factor.
`support_nddata`([_func, accepts, repack, ...]) | Decorator to wrap functions that could accept an NDData instance with its properties passed as function arguments.

### Classes

`BitFlagNameMap`() | A base class for bit flag name maps used to describe data quality (DQ) flags of images by provinding a mapping from a mnemonic flag name to a flag value.
`CCDData`(*args, **kwd) | A class describing basic CCD data.
`Conf`() | Configuration parameters for `astropy.nddata`.
`Covariance`([array, data_shape, ...]) | A general utility for storing, manipulating, and I/O of covariance matrices.
`Cutout2D`(data, position, size[, wcs, mode, ...]) | Create a cutout object from a 2D array.
`FlagCollection`(*args, **kwargs) | The purpose of this class is to provide a dictionary for containing arrays of flags for the `NDData` class.
`IncompatibleUncertaintiesException` | This exception should be used to indicate cases in which uncertainties with two different classes can not be propagated.
`InvalidBitFlag` | Indicates that a value is not an integer that is a power of 2.
`InverseVariance`([array, copy, unit]) | Inverse variance uncertainty assuming first order Gaussian error propagation.
`MissingDataAssociationException` | This exception should be used to indicate that an uncertainty instance has not been associated with a parent `NDData` object.
`NDArithmeticMixin`() | Mixin class to add arithmetic to an NDData object.
`NDData`(data[, uncertainty, mask, wcs, meta, ...]) | A container for `numpy.ndarray`-based datasets, using the `NDDataBase` interface.
`NDDataArray`(data, *args[, flags]) | An `NDData` object with arithmetic.
`NDDataBase`() | Base metaclass that defines the interface for N-dimensional datasets with associated meta information used in `astropy`.
`NDDataRef`(data[, uncertainty, mask, wcs, ...]) | Implements `NDData` with all Mixins.
`NDIOMixin`() | Mixin class to connect NDData to the astropy input/output registry.
`NDSlicingMixin`() | Mixin to provide slicing on objects using the `NDData` interface.
`NDUncertainty`([array, copy, unit]) | This is the metaclass for uncertainty classes used with `NDData`.
`NoOverlapError` | Raised when determining the overlap of non-overlapping arrays.
`PartialOverlapError` | Raised when arrays only partially overlap.
`StdDevUncertainty`([array, copy, unit]) | Standard deviation uncertainty assuming first order gaussian error propagation.
`UnknownUncertainty`([array, copy, unit]) | This class implements any unknown uncertainty type.
`VarianceUncertainty`([array, copy, unit]) | Variance uncertainty assuming first order Gaussian error propagation.

## astropy.nddata.bitmask Module

A module that provides functions for manipulating bit masks and data quality (DQ) arrays.

### Functions

`bitfield_to_boolean_mask`(bitfield[, ...]) | Converts an array of bit fields to a boolean (or integer) mask array according to a bit mask constructed from the supplied bit flags (see `ignore_flags` parameter).
`extend_bit_flag_map`(cls_name[, base_cls]) | A convenience function for creating bit flags maps by subclassing an existing map and adding additional flags supplied as keyword arguments.
`interpret_bit_flags`(bit_flags[, flip_bits, ...]) | Converts input bit flags to a single integer value (bit mask) or `None`.

### Classes

`BitFlagNameMap`() | A base class for bit flag name maps used to describe data quality (DQ) flags of images by provinding a mapping from a mnemonic flag name to a flag value.
`InvalidBitFlag` | Indicates that a value is not an integer that is a power of 2.

## astropy.nddata.utils Module

This module includes helper functions for array operations.

### Functions

`add_array`(array_large, array_small, position, *) | Add a smaller array at a given position in a larger array.
`extract_array`(array_large, shape, position) | Extract a smaller array of the given shape and position from a larger array.
`overlap_slices`(large_array_shape, ...[, ...]) | Get slices for the overlapping part of a small and a large array.
`subpixel_indices`(position, subsampling) | Convert decimal points to indices, given a subsampling factor.

### Classes

`Cutout2D`(data, position, size[, wcs, mode, ...]) | Create a cutout object from a 2D array.
`NoOverlapError` | Raised when determining the overlap of non-overlapping arrays.
`PartialOverlapError` | Raised when arrays only partially overlap.