Beginner in the forum and in with PTM-RTI :) DOUBTS AND DISCUSSION ABOUT TERMINOLOGY

[MIRIAM LT]

Hello,

My name is Miriam Luciañez Triviño, I am a Basque Government Pre-doctoral Research Fellow at the University of Seville (Prehistory and Archaeology Department). I have graduate and Master’s degrees in Cultural Heritage Conservation and Restoration, as well as a Master’s degree in Archaeology.

My research is focused on the manufacture, use and exchange of ivory objects in Iberian Late Prehistory, and the conservation/ restoration of archaeological ivory.

I am interested in use PTM-RTI to study ivory objects with two principal aims: 1. See the condition of the surface before and after the conservation-restoration treatment, and 2. Study the marks on the surface of the objects produced by the tool and the marks of use during the lifespan of the objects.

I am really new in the field of the PTM-RTI and I have a doubt about the terminology. Reading the bibliography, I am not able to understand the difference between the terms Polynomial Texture Mapping, Polynomial Texture Map(s) and Reflection Transformation Imaging. Maybe there a very slight difference, but many questions come to my mind like: When happened the change from using PTM to use RTI, are they the same technique? Have PTM and RTI the same mathematical background?

Could someone clarify me the current use of these terms, there is a consensus about it?

Thank you very much.

Miriam

[Claire Woodhead]

Hello Miriam,

There are others in the forum that know far more about this than me but as far as I know, on a basic level, a ptm is the type of file produced by the RTI process. Hope that helps!

Claire

Sent from my iPhone

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[Tom]

Miriam,

When we developed the PTM method at HP Labs back in 2001, we named it Polynomial Texture Mapping, thinking its main application would be in 3D rendering, specifically applying realistic, lighting sensitive textures onto 3D geometry. It was an extension of the ubiquitous Texture Mapping technique developed by Jim Blinn back in 1978. 

Although it did get used for that application (Toy Story II, ...), it found more use as a tool for capturing the appearance of a surface and then viewing that surface afterwards under user controlled lighting direction and material properties; what you'all do with it. In fact its most powerful ability is to transform the reflectance properties of that surface to a new material type, through the use of 'specular enhancement' and 'diffuse gain'. Technically, this isn't Texture Mapping, because you are not mapping those reflectance functions onto a 3D surface for 3D rendering purposes. Because of this, we redubbed it as Reflectance Transformation Imaging, RTI, since it captures the reflectance function for a surface and then allows one to transform that reflectance function to another material type. RTI is also a generalization of PTMs, polynomials don't have to be used. Although often the polynomial representation (from PTM) is used in CHI's RTI viewer, other representations like Hemispherical Harmonics can also be used. 

The terminology certainly is confusing, sorry about that.

Tom

[MIRIAM LT]

Thank you very much Claire and Tom. I am very grateful!

Regards,

Miriam