Did Leonardo Da Vinci, and possibly one of his students, intentionally create this stereoscopic pair?
The researchers, of course, can't be sure one way or the other, but Carbon points out that Da Vinci "intensively worked on the 3-D issue." In addition, in inventory lists there were hints of the existence of two "Mona Lisa" paintings on his property at the same time, and that he owned colored spectacles, Carbon said. [Leonardo Da Vinci's 10 Best Ideas]
This evidence "might indicate that he did not only about the 3D issue theoretically but in a very practical sense in terms of experiments," Carbon added. Also, when looking at the original colors of the two paintings the only real difference was in the sleeves, in which they are reddish in one version and greenish in the other. "This could be a hint to Leonardo's approach to look at the two La Giocondas through red-green (red-cyan) spectacles," he said, similar to those one might don to watch a 3-D movie.
"Still, despite all these indications, we have not found final proof for our hypothesis," he said.
Others suggest the evidence isn't there for an intentional creation of a stereoscopic view for paintings.
For instance, the disparities between the two paintings for other areas of the body, not the hands, don't fit with them creating a stereoscopic pair, according to Arguin. "Most in contradiction with this notion is the fact that these disparities are largely oriented vertically, and not horizontally as would be required to replicate the left and right eye views," Arguin said.
He gave an example of Mona Lisa's face: "All the landmark location changes are of the same size. This would not be so in an adequate stereoscopic image since disparities should vary according to relief (i.e. distance from the observer)."
Arguin added of the study: "They are quite accurate in their statements, and their discussion of their findings is sensible and interesting."
Carbon and Hesslinger say they agree with Arguin's comments about the consistency of disparities in certain regions of the "Mona Lisa" paintings and the horizontal or vertical nature of some of the disparities between the two paintings.
"Ideally we need horizontal disparities to create a proper 3D impression, which we mainly revealed for the hands region," Carbon told Live Science. "This is also the reason for having focused on the hands region when reconstructing the 3D image and visualizing the 3D effect."
Carbon added: "As conclusion we would like to qualify the stereoscopic properties of this region 'remarkable' and 'intriguing,' particularly when we take into account that the base pictures stem from the very early years of the 16th century."