The results of the methods described here are not always easy to predict; experiments are necessary for each particular case of preservation. For example, some preservational modes of Burgess Shale fossils do not yield higher contrast using crossed nicols. Dark graptolitic shales are sometimes disappointing because both fossils and matrix extinguish almost completely under crossed nicols, yielding poorer contrast than without polarization of the light. Conversely, some plant fossils to which I have applied this method yielded such high contrasts that the digital camera captured practically only outlines; in such cases the use of photographic film, with its higher tonal range, may be advantageous.
In the examples of image interference given here, only a few methods (light polarization and colour separation) have been used to produce the alternative images. Obviously, other methods can be used to produce pairs suitable for image interference, such as different frequencies of lighting, different filters, and different detectors in an instrument (for example, secondary-electron versus backscattered-electron or cathodoluminescence detectors in a scanning electron microscope).
Finally, a number of systems for computerized image processing and analysis are available, some of them without charge (e.g., NIH Image). Using computer algorithms to find edges, select areas of certain colour or shape, filter out certain frequencies of noise, and so on, goes one step beyond the application of simple calculations uniformly across an image as demonstrated here, and so it may be seen as pattern analysis rather than imaging. At any rate, the discussion of such techniques would be the object of an entirely different article.