This error is happening because we do some outlier filtering on the reconstructed volumes prior to clustering. Thus, the 100 original reconstructions (set by the parameter PCA: number of reconstructions) are filtered down to 96. This number is smaller than the number of classes and thus our GMM clustering will fail.
In general, we recommend setting the parameter PCA: number of reconstructions to at least 3-5X the number of classes (e.g., 500 in this case). We’ll make this more clear in a future release!
Also of interest: I recently wrote up a quick explanation of how the PCA mode works here: PCA mode initialization in 3D classification - query - #3 by olibclarke. Note that in our experience, this initialization does not typically produce better volumes than just the ‘simple’ mode (which uses random sample backprojection) but we’re actively exploring how to improve this! We’re happy to hear any feedback for how it does in your case.
Hope that helps,
Valentin