Likelihood is:

Priors:

For there are two alternative priors that are useful.

- Flat prior:

where the range of is restricted to . - Or a prior encoding prior knowledge:

where represents the prior knowledge about the expected intensities in the image formation; is a parameter expressing the unknown scaling between the learnt prior distribution of parameters and the intensities in a new image; and is a constant, representing the (improper) flat prior on .

Parameters: