Moments

Moments#

class scarlet2.measure.Moments(component, N=2, center=None, weight=None)[source]#

Bases: dict

Base Moments class

Moments of the brightness distribution

The dict is accessed by keys, which denote the power of y/x of the specific Moment: m[p,q] = int dx dy f(y,x) y^p x^q.

Notes

Like all coordinates in scarlet2, moments are computed in (y,x) order.

Parameters:

  • component (Component or array) – Component to analyze or its hyperspectral model

  • N (int >=0) – Moment order

  • center (array) – 2D coordinate in frame of component

  • weight (array) – weight function with same shape as component

property centroid#

Determine centroid from moments

Returns:

Coordinates of the centroid in the pixel frame of the data that defines these moments

Return type:

array

clear() → None.  Remove all items from D.#
convolve(p)[source]#

Convolve moments with moments p

The moments are changed in place.

See Melchior et al. (2010), “Weak gravitational lensing with Deimos”, Equation 9

Parameters:

p (Moments) – Moments of the kernel to convolve with

Return type:

self

copy() → a shallow copy of D#
deconvolve(p)[source]#

Deconvolve moments from moments p

The moments are changed in place.

See Melchior et al. (2010), “Weak gravitational lensing with Deimos”, Table 1

Parameters:

p (Moments) – Moments of the kernel to deconvolve from

Return type:

self

property ellipticity#

Determine complex ellipticity from moments

Returns:

Ellipticity (2D) of the data that defines these moments

Return type:

jnp.array

fliplr()[source]#

Flip moments along the x-axis

The moments are changed in place.

Return type:

self

flipud()[source]#

Flip moments along the y-axis

The moments are changed in place.

Return type:

self

property flux#

Determine flux from 0th moment

Return type:

float

fromkeys(value=None, /)#

Create a new dictionary with keys from iterable and values set to value.

get(key, default=None, /)#

Return the value for key if key is in the dictionary, else default.

items() → a set-like object providing a view on D's items#
keys() → a set-like object providing a view on D's keys#
normalize()[source]#

Normalize moments with respect to the flux

Return type:

self

property order#

Moment order

Return type:

int

pop(k[, d]) → v, remove specified key and return the corresponding value.#

If the key is not found, return the default if given; otherwise, raise a KeyError.

popitem()#

Remove and return a (key, value) pair as a 2-tuple.

Pairs are returned in LIFO (last-in, first-out) order. Raises KeyError if the dict is empty.

resize(c)[source]#

Change moments for a change of factor c of the size/spatial resolution of the defining frame

This operation arises when one adjust the moments for a change in the size of pixels of the defining frame, e.g. when asking “what would the moments be if the pixels were factor c smaller (or the source c times larger)”? The fluxes are unchanged, which corresponds to preservation of photons under resizing.

The moments are changed in place.

See Teague (1980), “Image analysis via the general theory of moments”, eq. 34 for details.

Parameters:

c (float or list) – Scaling factor for the size change. Can be different along x and y

Return type:

self

rotate(phi)[source]#

Change moments for rotation of angle phi.

The moments are changed in place.

See Teague (1980), “Image analysis via the general theory of moments”, eq. 36 for details.

Parameters:

phi (float) – Rotation angle, in radian

Return type:

self

setdefault(key, default=None, /)#

Insert key with a value of default if key is not in the dictionary.

Return the value for key if key is in the dictionary, else default.

property size#

Determine size from moments

Return type:

float

transfer(wcs_in, wcs_out)[source]#

Compute rescaling and rotation from WCSs and apply to moments

The method adjusts moments measured with a frame defined by wcs_in to the frame wcs_out. The moments are changed in place.

Parameters:
Return type:

self

translate(shift)[source]#

Change moments for translation shift

The moments are changed in place.

Note: This changes all the moments, not just the dipole, for the new reference center.

See Teague (1980), “Image analysis via the general theory of moments”, eq. 30 for details.

Parameters:

shift ((y, x)) – translation, in pixels

Return type:

self

update([E, ]**F) → None.  Update D from dict/iterable E and F.#

If E is present and has a .keys() method, then does: for k in E: D[k] = E[k] If E is present and lacks a .keys() method, then does: for k, v in E: D[k] = v In either case, this is followed by: for k in F: D[k] = F[k]

values() → an object providing a view on D's values#
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