Aravind's Bio Spec


AK Imagery
Photo Blog

BioSpec is a model developed by Aravind Krishnaswamy and Dr. Gladimir Baranoski for the simulation of light interaction with human skin. The name BioSpec characterizes the two fundamental properties of this model, first that is Biophysically-based and second that it is a fully spectral model.

The term biophysically-based implies two properties of a model:

  1. The parameters to the model are biologically meaningfull. i.e. There aren't any ad-hoc parameters or parameters who existence cannot be biologically justified.
  2. The algorithms in the model are based on physics and optics.

Another contribution of the BioSpec model is in its validation. Rather than relying on the comparison of rendered images to validate the model, the BioSpec model is validated by comparing spectrophotometric and goniophotometric curves with that of actual measured skin data.

The images generated using the BioSpec model are used mainly to demonstrate the fact that it can be incorporated into a standard Monte Carlo renderer and to show the variety of skin types, conditions and effects the BioSpec model can simulate.

The image at the top of this page demonstrates the translucency of human skin in areas of the body where there is little subdermal tissue (such as the ears, between fingers, etc.). In the image above, the melanin concentration is increased going from left to right (very lightly pigmented to heavily pigmented). A powerful light source (6500K blackbody emitter) is placed behind the head.

In the images above, the condition of Erythema is simulated. Erythema is caused by the dialation of blood vessels followed by an increase of blood in the dermis layers. Examples of when erythema occurs is right after a sunburn or after light frostbite.

In the images above, the symptom of hyperbilirubinemia is simulated. Hyperbilirubinemia is associated with the accumulation of bilirubin in the dermal layer. It is usually caused by liver failure and causes the skin and eyes to appear yellow.

In the left image above, a human finger is rendered normally, in the next two images an extremely powerful light source is placed behind the finger to highlight the translucency. The amount of blood is increased between the second and third image.

Frames of an animation simulating the onset of erythema in the skin of a human ear as the head rotates.

If you want to learn more about the BioSpec model, you read the Eurographics 2004 paper or the technical report.

If you want to try and implement the BioSpec model yourself, having the data BioSpec uses will be valuable. The data tables BioSpec uses are available for download [BioSpecSkinData.h].

BioSpec source code is now available for download. These source files are taken from the R.I.S.E. rendering package.

[] - All source (including R.I.S.E. source) required to build the simple command line application.

[] - Only the BioSpec sources.

Hosted by

All text and images (c) 2000-2014 Aravind Krishnaswamy. All rights reserved.