Texture Maps (PTMs) are a simple representation for images of
functions instead of just images of color values. In an
conventional image, each pixel contains static red, green, blue
values. In a PTM, each pixel contains a simple function that
specifies the red, green, blue, values of that pixel as a
function of two independent parameters, lu and lv.
Typically, PTMs are used for displaying the appearance of an
object under varying lighting direction, and lu,lv specify the direction of a point light source. However, other
applications are possible, such as controlling focus of a scene.
PTMs can be used as light-dependent texture maps for 3D
rendering, but typically are just viewed as ‘adjustable images’.
PTMs are typically produced
with a digital camera by photographing an object multiple times
with lighting direction varying between images. Even a low-end
digital camera provides enough resolution to produce good PTMs,
and almost any light source can be used such as a light bulb,
LED or flash.
Tools for viewing PTMs are downloadable below, as
are tools for constructing your own PTMs from images. Given a
stack of images of an object under varying lighting direction,
one has collected samples of the object’s reflectance function
at each pixel. Independently for each pixel, the PTMfitter fits
a low order polynomial to those samples to produce a PTM. The
PTMviewer simply evaluates this polynomial in real time
independently for each pixel to produce an image.
This can be
done at real-time rates on even low-end computers because of the
simplicity of the polynomial, allowing interactive control of
lighting direction. In addition, once the reflectance functions
are represented in this manner, they can be transformed to make
the surface detail existing on the object more apparent. We call
and an example on a 3000 year old cuneiform tablet is shown
appears in Siggraph 2001 proceedings (4.9 MB)
presented at Siggraph 2001 (2.45 MB)
Java based Interactive
Relighting the Antikythera Mechanism
Smithsonian Institutes page with >400 interactive examples
Heritage Imaging's PTM / RTI links
blog describing many recent archeological applications
Southampton Archaeological Computing Research Group PTM demo
Downloads of PTMviewer, PTMfitter, Sample PTMs, etc.
Download PTM Builder
Antikythera Mechanism download page
in Paleontology »
New: Google Tech Talk
New: EconomistArticle »
New: Scientific American Article
Ancient Inscriptions in Virtual Light," USC's West Semitic