def check_overscan(xstart, xsize, total_prescan_pixels=<NUM_LIT>,<EOL>total_science_pixels=<NUM_LIT>):
hasoverscan = False<EOL>leading = <NUM_LIT:0><EOL>trailing = <NUM_LIT:0><EOL>if xstart < total_prescan_pixels:<EOL><INDENT>hasoverscan = True<EOL>leading = abs(xstart - total_prescan_pixels)<EOL><DEDENT>if (xstart + xsize) > total_science_pixels:<EOL><INDENT>hasoverscan = True<EOL>trailing = abs(total_science_pixels -<EOL>(xstart + xsize - total_prescan_pixels))<EOL><DEDENT>return hasoverscan, leading, trailing<EOL>
Check image for bias columns.

    Parameters
    ----------
    xstart : int
        Starting column of the readout in detector coordinates.

    xsize : int
        Number of columns in the readout.

    total_prescan_pixels : int
        Total prescan pixels for a single amplifier on a detector.
        Default is 24 for WFC.

    total_science_pixels : int
        Total science pixels across a detector.
        Default is 4096 for WFC (across two amplifiers).

    Returns
    -------
    hasoverscan : bool
        Indication if there are bias columns in the image.

    leading : int
        Number of bias columns on the A/C amplifiers
        side of the CCDs ("TRIMX1" in ``OSCNTAB``).

    trailing : int
        Number of bias columns on the B/D amplifiers
        side of the CCDs ("TRIMX2" in ``OSCNTAB``).