nmrglue.process.proc_bl.poly_fd

nmrglue.process.proc_bl.poly_fd(data)

Polynomial frequency domain baseline correction

From NMRPipe paper (appendix):

applies a polynomial baseline correction of the order specified by argument -ord via an automated base-line detection method when used with argument -auto. The defauly is a forth-order polynomial. The automated base-line mode works as follows: a copy of a given vector is divided into a series of adjacent sections, typically eight points wide. The average value of each section is subtracted from all points in that section, to generate a ‘centered’ vector. The intensities of the entire centered vector are sorted, and the standard deviation of the noise is estimated under the assumption that a given fraction (typically about 30%) of the smallest intensities belong to the base-line, and that the noise is normally distributed. This noise estimate is multiplied by a constant, typically about 1.5, to yield a classification threshold. Then, each section in the centered vector is classified as base line only if its standard deviation does not exceed the threshold. These classifications are used to correct the original vector.

Alg:

1. Divide into ‘blocks’
2. Center each block and create centered vector
3. Calculate intensity (abs) of each centered vector
4. Sort intensities, lower 30% belong to baseline
5. Fit base line intensities to Normal distribution, gives estimation of standard deviation (std) of noise
6. Classification threshold set to 1.5*std
7. Qualify each block in centered vector as baseline only (its std < thres) or not (std > thres)
8. Fit baseline only points to polynomial and substract off