Brainstorm and implement a suite of metrics

[xuod]

This issue is meant to be a place for brainstorming about various metrics which will then be implemented in btk.metrics.

• low-level metrics:

  • detection: detection of a blend, detection of the correct number of objects in a blend, accuracy of the position of the centers of objects
  • segmentation: quality of the masks
  • deblending: pixel-wise comparison, blendedness (as defined in the Scarlet paper)

• high-level metrics involving measurements:

  • flux/colors
  • photo-z: bias
  • size and shape
  • shear:
    • selection effects
    • exclusion bias
    • impact on shear estimators

[sowmyakth]

A basic version implemented in Implemented in #13 which compares detected centers and true centers.