imageHugh Farey has prepared a helpful, four page, image rich PDF document on Banding on the Shroud of Turin. He points out, for instance, in referring to this image on the right:

This is the top of the alleged band which Barrie
Schwortz felt needed adjusting in density to
restore the image to a more realistic
appearance. It is two ‘pitches’ (1) wide, and
defined on the right by a bunch of thin warp
threads (2) forming the prominent stripe
visible on the Enrie image, and on the left, less
clearly, by the adjacent pitch (3), which is
darkened by ‘hair.’

Hugh concludes:

Conclusion. The weave of the cloth does produce the illusion of bands according to its illumination, which serve to enhance a viewer’s perception of the intensity of the image at various places, and give the illusion of over-defined dark and light bands in various places which are not as clearly vertical sided as they appear.. So the light vertical areas defining the sides of the cheeks are really present, but they are not as precise or as well defined as they appear, and are not merely artifacts of the cloth, but real areas where the image making process just didn’t happen.