Figure 3.

Performance. Means and standard deviations for time and error measures (10 repetitions) for exact and approximate PCA. Number of pixels c is given in % of the total number n. Running times (Intel Core Duo T6400, 2GHz) are for the entire Algorithm 3, including computation of probabilities. All measurements are for rank-k = 30 approximations, as we found that 20-30 components are typically sufficient to detect all glomeruli. Lower principal components only explain more of the noise (see also Figure 4).