Asymmetric Least Square Smoothing
Features:
The filter is based on asymmetric least squares smoothing for multiple spectra baseline correction. The algorithm also eliminates scatter effects on the spectra.
For large images, Asymmetric Least Square Smoothing might be computationally expensive. The algorithm might take several minutes depending on the size of the image and the number of iterations. We recommend using Spectrum Background Removal implemented in the Feature Finder toolbox from the Toolbox menu to optimize parameters.
Steps:
1. Load a file and select Filtering and Enhancements → Asymmetric Least Square Smoothing.
2. Select the smoothing parameters from the pop-up dialog.
Smoothness defines how smooth the baseline should be (default 100).
Asymmetry defines how "low" the baseline should be. The range is from 0 to 1. Lower peaks require asymmetry approaching 0, while high peaks require asymmetry value approaching 1.
Iterations defines the number of iterations to reach the converge (default 20). The calculation time is proportional to the number of iterations.
3. Press Apply and visualize the smoothed image after the computation is complete.
4. (optional) Click Multi-Spectra Mode in the SPECTRAL ANALYSIS panel and draw a region of interest to visualize the spectrum before and after the smoothing procedure. The original spectrum (shown as mean +/- standard deviation) shows numerous sharp peaks related to noise. After filtering, the new spectrum shows no sharp peaks and much smaller standard deviation.
We recommend using Feature Finder toolbox to optimize filter parameters. Feature Finder toolbox has an option to generate three spectra: the original spectrum (green line), the baseline spectrum (red dotted line) and the corrected spectrum (blue solid line). Corrected spectrum = Original spectrum – Baseline Spectrum.
Reference:
Eilers, P. H., & Boelens, H. F. (2005). Baseline correction with asymmetric least squares smoothing. Leiden University Medical Centre Report, 1(1), 5.
