Some processing algorithms can be applied, starting from digital images, to detect computer contents otherwise invisible if observed directly.

It is necessary to pinpoint that computer methodologies allow to have information that are in the original image already but not immediately visibile without introducing any artificial content.

It is also necessary to pinpoint that, even if the Shroud has colorimetric gradations (yellow), the digital processing mainly uses images represented with shades of grey, between white and black; in fact, the purpose is to bring out the information and not to keep the original color appearence.

Grey variation images are used anyway in most of the applications that mainly consider them monochrome sources just like the biomedic one, for example.

Processings aim at making the information which is integral to images more usable to the human eye; they are based on the application of quality improvement methods whose core issue are both proceedings to brighten the grey levels up and of filters. Modifying the levels of grey means to affect the contrast (namely, variate brightness) and consequently increasing the ability to discern the details. Filters, on the other end, are applications of physical – matematical concepts that process a pixel brightness on the basis of the values of a surrounding area and correlating them. Processings are also based on the physiology of vision. In fact, the human eye can perceive the brightness differences that are linked to details only if they differ in a value concerning the sensitivity to contrast because that is what characterizes the eye response. Since the eye normally perceives about fifty levels of grey it is necessary to fix the distribution of levels of grey increasing the contrast once again again in order to improve an image clearness. It may be necessary, when processing monochrome images, to turn the levels of grey into color so that human eye can immediately evaluate any particular image information. This method is the so called pseudo-colour method and is based on the fact that the eye has a strongest ability to perceive colours rather than levels of grey.

On the other hand, the processing filters are normally used to remove the noise distorting or hiding an image information or rather to enhance those brightness transitions by the image structures outlines. The use of filters to remove the noise is potentially dangerous since, while having an effect on intereferences, it may also alter the signal softening or even cancelling the interesting details. But if the cancelled information is not linked to the examined structure, then the filters application actually improves image quality.

In the Shroud case, the problem is to enhance the details and the peculiar image behaviour.

The first official photograph of the Shroud, taken by the lawyer Secondo Pia in 1898 on a monochrome plate, stressed one of the characteristics of the image on the Shroud, that is its negativity: all information about the anatomical parts that define the body figure are dark just like on the film. On the other hand, bloodstains are positive since they are dark in their nature.

There is also another unusual and more important characteristic linked to negativity: tridimensionality. A tridimensional object extends in the three directions: width, height and depth. Therefore, an image is tridimensional if it is possibile to draw its structures spatial information. This fact appears through brightness intensity gradations that depend on the distance from the acquisition system: in the case of the Shroud traces are dark if by in relief areas and light in other areas.

So, the digital Shroud image processing to determine the impression tridimensionality, has allowed to obtain new images that highlight the relief and details not visible on the original image.