Algorithem 3.1.

Ridge-tracing Normalization.

Perform quantile normalization to all reference channels of all arrays (Bolstad et al., 2003), if multiple arrays are presented, Generate 2D probe density via 2D kernel smoothing with normalized reference intensity and transformed sample intensity by maintaining the same log-ratio for each probe, Trace the ridgeline from 2D density by first determining the highest peak and then walking along the ridgeline, and Regress the ridgeline to provide normalization standard.