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Ways to Proceed

There are certain behaviours that need to be looked at systematically:

• Investigate the warp fields for insight into displacements in terms of number of pixels.
• Learn the re-sampling errors (if any) using synthetic data.
• Study the rate at which displacement (in terms of pixels) increases for a given perturbation scheme.
• Learn how distributions vary across the image regions.

What follows are suggestions, which can improve the current scheme for perturbing the data:

• Reduce the size of warps and use a larger number of them.
• Define a spatial constraint which the centres of warps are subjected to.
• Extend the image boundaries and fill these with appropriate grey-level values. This will cater for more freedom of pixel movement.
• (Carole) Warps need to be aggregated. In other words, if perturbation is based on warps, then at each stage one has to add new warp/s atop the existing ones - the ones from previous perturbation steps.