constant_spectral_offset#

constant_spectral_offset(y, filter_window=5, filter_dim=2, ratio=0.1)[source]#

Get constant offset of spectral baseline.

This function searches constant offset by finding a region where 1st and 2nd order differentiation are close to zero. A return value is an average y value of that region. To suppress the noise contribution to derivatives, this function also applies a Savitzky-Golay filter to y value.

This method is more robust to offset error than just taking median or average of y values especially when a peak width is wider compared to the scan range.

Parameters:

  • y (ndarray) – Array of y values.

  • filter_window (int) – Window size of Savitzky-Golay filter. This should be odd number.

  • filter_dim (int) – Dimension of Savitzky-Golay filter.

  • ratio (float) – Threshold value to decide flat region. This value represent a ratio to the maximum derivative value.

Returns:

Offset value.

Return type:

float