18. Dataset Downsampling

18.1. Concept

Dataset downsampling is explained in the Basic Concepts section (above).

18.2. Changing dataset downsampling

The current dataset downsampling levels can be changed using the Change downsampling command on the File menu. This opens a dialog that prompts for a new Z (sparsity) factor, and a new XY factor. Either or both can be changed. If the Z factor is decreased, previously unused slices will be brought into play. The user has the option of whether or not to interpolate masks (and locks/selects) and curves onto these slices; if the appropriate box is selected, masks, locks and curves are created for new slices by copying from one of the existing adjacent slices. If not, these are left blank (or any pre-existing data used, e.g. from before a downsample had taken place). If in doubt, it is best to interpolate.

Changing downsampling on the fly like this is allowed for, but is not to be taken lightly – it is a major operation, which takes some time to complete, and will result in either the discarding of data (downsampling) or potential differences in editing of areas (upsampling with later editing of certain regions).

18.3. Dataset downsampling for rough masking

As mentioned in Basic Concepts, an entire dataset can be masked while downsampled to some low resolution, and then the dataset upsampled. This will result in blocky-edged masks, but so long as these edges are in space not on the specimen this will not matter. After doing this all slices will need to be re-generated at the new (higher) resolution, so all threshold corrections done with brightening or segment drawing will be lost. If a user intends to upsample at any point prior to outputting the finished model, they should put off any such editing until AFTER upsampling.