# scarlet Documentation¶

scarlet is an open source python library for modeling astronomical sources from multi-band, multi-epoch, and multi-instrument data.

# Change Log¶

## 1.1 (2020-07-14)¶

### General¶

• Introduction of Spectrum and Morphology classes (both inherited from Factor) to modularize FactorizedComponent. They implement get_model member functions which create the representation of the spectrum and morphology model from whatever it uses as parameters.

• Component.sed has been renamed to Component.spectrum.

• Component.morph has been renamed to Component.morphology.

• FunctionComponent has been deprecated.

• Initialization and plotting functions are now consistent for multi-observation data sets.

### New Features¶

• One can now e.g. combine a custom spectrum model with an existing PointSourceMorphology.

• Box can now be sliced for lower dimensional subset; two Boxes can be combined with @ to create a higher-dimensional box.

• display functions can now show the source boxes.

## 1.0 (2019-12-22)¶

### General¶

• Complete overhaul of the modeling code. It now allows for arbitrary Parameter instances to generate a source model (e.g. point-source or Sersic fitting).

• Each Parameter can be further constrained by proximal constraints or priors.

• New optimizer from the proxmin package: adaprox is an adaptive proximal gradient method that doesn’t require Lipschitz constants and uses different steps sizes for each element of an optimization parameter.

### New Features¶

• Prior can now be attached to a Parameter and its gradient will be added to likelihood gradients.

• PointSource performs optimization of centroid position and flux assuming the model PSF.

• Fourier helps with the bookkeeping involved with calculating FFTs to different shapes.

• Most scarlet objects can be pickled. That allows to store sources and reload sources.

• Component has Box to confine its footprint and save memory.

• scarlet.display has methods to show_scene and show_sources which allow fast inspection.

• scarlet.measure has methods to perform measurements on the component models.

### API Changes¶

• Frame and Observation strongly prefer all arguments (weights, psfs, channels, wcs) to be set.

• Frame.psfs (or Observation.Frame.psfs) now stores a PSF object, and the PSF.image method needs to be called to access the PSF image cube.

• ExtendedSource does not accept bg_rms keyword. This information is derived from observation.weights.

## 0.5 (2019-06-26)¶

### General¶

• PSF convolutions are now performed on the model of the entire blend as opposed to individually for each source.

• Blend no longer fits for source positions. Instead it is up to the user to implement a centering algorithm, such as centroiding or the scarlet.update.fix_pixel_center.

• Updates to all of the docs and tutorials to match the new API.

### New Features¶

• Multi-resolution deblending.

• A BoundingBox container to define rectangular regions in the pixel grid, a trim function to strip away all pixels lower than a cutoff value, and a flux_at_edge method to determine if a model has flux on the edge of the image.

• A Scene class to handle the metadata for the deblended model.

• An Observation class to provide mappings from the model scene to a set of observations with potentially multiple filter bands.

• A LowResObservation class for observations with lower resolution than the blended model, requiring resampling and reprojection.

• A BlendFlag has been introduced to keep track of things that might have gone wrong while debending.

• A gradient Prior class has been created to allow users to update the gradient of a parameter in a source or Component.

• Color normalization imports from astropy.visualization, with the addition of img_to_channels to map any number of filter bands to an RGB that can be displayed.

• A CombinedExtendedSource initializes sources with multiple observations at different pixel resolutions.

• Frame issues warnings when PSF is not specified or not normalized.

• Frame.channels is used to identify channels in multiple observations.

• PSF convolutions and ffts of image cubes are performed using ndimensional fft along selected axes for better performance.

### API Changes¶

• Scene is a is a confusing name and has been renamed to Frame.

• Observation.get_model is a confusing name and has been renamed to Observation.render.

• Blend does not have a frame argument any more, it inherits its frame from sources.

• Component is now the base class for sources and Source has been removed PointSource, ExtendedSource, and MultiComponentSource are now inherited from Component.

• The Constraint class and module were removed in place of an update method that has been added to Components (and thus sources). User defined constraints should now inherit from Component or one of its subclasses and overwrite the update method. Constraints are now applied using functions from the scarlet.update module or similar user defined update functions.

• get_model has been simplified for ComponentTree and Components to always return the entire scene with the component added in place, using the Scene target PSF. To get a model in the same space as observations requires calling Observation.get_model and passing the high resolution/best seeing model.

• Frame has a channels argument instead of filter_curves.

• The old resampling.py module has been renamed interpolation.py and a new resampling.py used for multi-resolution resampling/reprojection.

• Sources and components are no longer centered in a small patch that is reprojected into the model frame. Instead components can exist anywhere on an image and constraints that require a center, such as symmetry and monotonicity, can use the new uncentered_operator method.

• make_operator is now a method of the LowResObservation class as should be.

## 0.45 (2019-3-27)¶

### General¶

• Tests have been added for the operator, constraint, resample, and transformation modules. Tests are run on Travis CI with each new build.

### New Features¶

• Convolutions can now be done in Fourier space and/or real space by setting the use_fft option in config.Config.

• A new internal function was added to project images into larger or smaller images by slicing and/or padding.

• Interpolation kernels have been implemented for fractional pixel shifts using bilinear, cubic spline, and Lanczos algorithms.

## 0.4 (2019-2-15)¶

### General¶

• Dropped python 2 support

### New Features¶

• Initialization of PointSource, ExtendedSource, and MultiComponentSource now take normalization as an input parameter, which selects the normalization used to break the color/morphology degeneracy. The default is to use constraint.Normalization.Smax, which normalizes S (morphology) so that the peak pixel always has a value of one.

• The exact_lipschitz option has been added to Config. This allows the user to recalculate the Lipschitz constant (used for calculating step sizing) in each iteration as opposed to an approximation (the default) used for speed.

### API Changes¶

• The default value of the Config parameter accelerated is now False. This was done because in some cases acceleration caused the optimization to diverge, and because the new S matrix normalization causes the code to run faster than the old accelerated version for most blends.

• Due to the additional normalization parameters, a get_flux method has been added to properly get the flux of an object in each band.

### Bug Fixes¶

• Monotonicity would break if the bounding box for a Source was not odd. The shape is now forced to be odd when the Source is initialized.

• fix_sed and fix_morph were not correctly passing the SED and morphology though correctly, but this behavior has been corrected.

• Installations that do not have access to get the current commit using git will now truncate the release number to the subversion. This was needed for binary installs (like the LSST-DM stack).