The negativity of the image appears observing the film used to photograph it: as a matter of fact, there is an image on the photo negative whose light and shade effects and, of course, the spatial transposition are totally flipped left to right. Even the bloodstains seem to be light but it is necessary to remember that, since in nature they are dark, they are positive on the Cloth.

The photographic copies reproducing the figure in its original aspect are then obtained from the photo negative. Figure 1 shows the positive and the negative of the facial image obtained from the 1931 cav. Giuseppe Enrie official picture.

If one observes the facial image positive (fig. 1 on the right), one can clearly see some dark marks by the cheekbones and, on the forehead left side, a garish dark bloodstain in the shape of a turned over "3"; in the photo negative (fig. 2 on the left) the marks by the cheekbones are light just like the bloodstain that nevertheless appears on the forehead right side in the shape of a "3" due to the spatial transposition effect.

If the Shroud was forged someone should have painted a man figure in negative; this is innatural and certainly could not be realized by any medieval forger because at that time the principles of photography, set forth around 1850, were still unknown.

The difference between the tones of the light and dark values of the photographic positive is so tiny that the eye can only perceive a human face traits as a whole without picking out the details. In this image little dark spots can be seen clearly and are random but thickened in the clear areas where the mark is weaker; these spots are very likely the results of the many ups and downs in the Cloth history during the centuries. On the other hand, the horizontal and vertical lines that can be made out on the image are mainly caused by the tissue texture and the cloth folds. These inconveniences are not only a cause of aesthetic deterioration but an obstacle to the following image process analysis too.

As mentioned before, the image observation underlines that the marks correlated to the in relief anatomical parts, like the nose and the cheeks, are dark while they are clear in the other areas like in the orbital and the jawbones areas. The image therefore represents a face whose brightness is distributed exactly in an opposite way to the one we perceive in everyday reality when, in fact, the more prominent the parts are the more clear they are perceived.

On the other hand, the light and shade effects in the photo negative are are totally flipped left to right and there is the spatial transposition. That is why the clear cloth seems to be dark whereas spots corresponding to the anatomical areas in relief become clear with intensity gradations that follow the human face curves. the photo negative therefore represents the positive aspect of a man as if we could observe him standing in front of us.

On the left side, figure 2 represents the face image converted numerically for the following processing whose result is shown on the right side.

The numerical image has been obtained by video camera and acquisition device that converted a 24X36 slide luminous information, reproducing the the 1931 cav. Giuseppe Enrie official picture, in a 512x512 resolution with 256 grey levels bidimensional image.

A “median” filter, analysing the pixels inside a square window and subsituting the brightness values if not coherent to those of the considered area, has been used to reduce all the inconveniences. On the right part of figure 2 one can see the application of a median filter on the photo negative makes the noise disappear and the image more clear. Moreover, the contrast is high and the connection signal/inconvenience is useful to any other image analysis.