So,
not too many computer-related issues in the last example, but… now let’s look
at impact of reproduction at a whole new
level…
Michelangelo, when he was painting the
Sistine chapel really wanted to be creating sculpture—he was forced to paint
it against his wishes.
One
of his most famous sculptures is his David.
Goal
of Digital Michelangelo Project was to make a 3D model that people can explore
from any point of view, different lighting,
etc.
Visual
Culture:
History: It’s David from David Goliath story in the bible.
The
statue of David was started by a different artist, Agostino di Duccio, in
1463. He picked out a rather narrow
piece of stone, which was customary for artists of his denomination.
If you are an art expert, you can see
from the side that this is not a
piece that Michelangelo would have picked. It is too thin. http://vlsi.colorado.edu/~rbloem/david.html
Politically:
resonated with Florence and its situation within the city state of Italy
Also,
aesthetically very beautiful sculpture.
Already
several full-scale replicas in Florence.
Computer
Graphics and Visualization (CS): The
Stanford project, led by Marc Levoy, was a heroic proof-of-concept project costing millions of dollars.
Not
replicable/scalable at this point. Going to tell you a bit about it because:
fascinating project, demonstrates some of the many implications of visual computing for fields from art to tourism to
philosophy, as well as technical issues in computer graphics (papers on project published at SIGGRAPH and
elsewhere).
•3D scanning not new: People scan 3D stuff all the time,
cheap devices, used for movie special effects, etc., etc. but really good quality, accuracy of large-scale delicate rare
unmovable art works is a different story.
•
•Sampled sculpture at less than 1mm intervals (it’s over
5feet tall)
•
•Scanned with customize device but some parts of surface
self shading—had to use hands canners. Still spent hours trying to fill in missing data—holes in the final model.
•
•Dealt with
--had
to hire 24 security guard
--had
to have shifts and scan all night to get done in time frame of grant and
italian gov.
--had
to use manual controls and encase parts of the scanner in foam to ensure no
accidental damage to sculpture
--had
to account for light falloff from actual lighting to create accurate model of
surface that could be lit any way a user
desires in a 3D scene
--data
sets huge (many gigabytes) and hard to deal with.
•
•
•2mm accuracy
•4 million polygons—triangles-- in the head.
•8 million for entire statue.
•
•Raw data was over 2 billion triangles
•
•Head takes 12 hours to render.
•
•Veining and reflectance artificial. Renderings include
physically correct subsurface scattering, but with arbitrary parameters.
•Data for flawless, watertight, full-resolution model of
the entire statue, with color = 2 billion polygons and 7,000 color images,
occupying 32 gigabytes.
•3D graphics in general incorporates most of the concepts
learned in 2D graphics—the texture maps and “7000 color images” referred to
are all raster data—something we’ll be
learning about in a few weeks. Artists , scientists, art historians, and
others will need to know the basic terminology and concepts in this
field.
•
Harder
to make this data useful than originally thought—needed cleaning” and
datatsets are huge. http://graphics.stanford.edu/data/mich/
Digital
Michelangelo Project
Model
issues: noisy data, misaligned meshes, holes.
Sounds
conceptually simple but very challenging—equipment, logistics, angle of laser
when scanning, scattered light from marble
surface, dirt on sculpture, limits on dataset size (huge but could have
captured more info, but dataset would have been
unmanageable). Vibrations,
<1mm
to 5feet tall for david. Huge dynamic range 20,000 to 1.
“However,
reconfiguring the pan-tilt [scanning] assembly proved more problematic. In
retrospect, this should not have surprised
us; 11 microns of play - 1/10 the diameter of a human hair - in a pin and
socket joint located 5 cm from the pan axis
will cause an error of 0.25 mm at our standoff distance of 112cm. In general,
we greatly underestimated the difficulty of
reconfiguring our scanner accurately under field conditions.
Range
scanning. A typical range scan
consisted of several concentric curved shells separated by translational
motion of the scan. We often spent hours
positioning the gantry in fruitless attempts to fill holes in our model of the
David.
Issues
of laser possibly damaging statue –no.
But
did have to use manual controls for automatic scanner head movement to ensure
no damage. scan head encased in foam
rubber.