[Swordmaker]

I might note, that so far in my work with the image — occupying not more than 20 minutes total — I have seen a pronounced bias or preferred direction of incident lighting.

Which direction?

Your 20 minutes, I believe, are trumped by the years of experience and expert knowledge of many photographic experts who have spent far more time manipulating the images of the Shroud. They do not find directionality of light and in fact find no natural shadow artifacting at all.

The Photoshop embossing effect is created by color reversals (positive/negative) and offsets of the resulting layer to produce a pseudo 3D effect. The pseudo directionality of the light source depends on which direction (angle) the offset is made. Change the direction of offset and you change the pseudo shadowing direction indicating a light source from another direction.

The first picture above has the offset of the negative layer to the right, giving the appearance of being lit from the left with the pseudo shadows on the right. The second has the negative layer offset to the left, giving the appearance of being lit from the right, with the pseudo shadows on the left.

I have done this by hand, creating a negative layer of the positive, superimposing a semi-transparent layer of one over the other and offsetting the upper layer by a small amount. One can easily change the pseudo shadows by merely moving the upper layer around the lower.

Your "pronounced bias" is there. You do see it. However, it is an artifact of the default settings of the Photoshop emboss filter. It is not inherent in the Shroud's image.

[js1138]

Two things:

You cannot get a 3D effect from this image without inposing a pseudo iight source.

Secondly, the direction matters. Except for a couple of priveleged directions, most directions produce a jumble or a lessened effect. The information in the original image has a directional bias.