Photometric Calibration

The PhotometricCalibration class provides methods for performing photometric calibration of astronomical images. It supports:

Photometric calibration using external reference catalogs.
Application of saved zero points, color terms, and magnitude terms.

Note

After performiong photometric calibration, header keywords related to zeropoints are updated.

Usage Examples

Basic Photometric Calibration

from ezphot.methods.photometriccalibration import PhotometricCalibration
from ezphot.imageobjects import ScienceImage
from ezphot.dataobjects import Catalog

sci = ScienceImage("example.fits")
catalog = Catalog("example.cat")

calib = PhotometricCalibration()

# Perform photometric calibration using GaiaXP catalog
sci, catalog, refcat = calib.photometric_calibration(
    target_img = sci,
    target_catalog = catalog,
    catalog_type = "GAIAXP",
    mag_lower = 13,
    mag_upper = 15,
    visualize = True,
    save_fig = True
)

print("Calibrated catalog:", catalog.data[:5])

Applying Zeropoints

If you have already run the calibration step in Basic Photometric Calibration, you can directly apply the saved zeropoint from the FITS header to your catalog:

updated_catalog = calib.apply_zp(
    target_img = sci,
    target_catalog = catalog,
    save = True
)

print(updated_catalog.data.columns)

Applying Color Terms

If you have already run the calibration step in Basic Photometric Calibration, you can directly apply the saved color term for zeropoint from the FITS header to your catalog:

updated_catalog = calib.apply_color_terms(
    target_img = sci,
    target_catalog = catalog,
    comparison_catalog = refcat,
    max_distance_second = 2.5,
    save = True
)

Applying Magnitude Terms

If you have already run the calibration step in Basic Photometric Calibration, you can directly apply the saved magnitude term for zeropoint from the FITS header to your catalog:

updated_catalog = calib.apply_mag_terms(
    target_img = sci,
    target_catalog = catalog,
    save = True
)

Note

All photometric calibration results are saved into the FITS header of target_img and propagated into the ezphot.dataobjects.catalog.Catalog as new columns (e.g., MAGSKY_*, ZP_*, UL3_*, UL5_*).