Monday, June 08, 2009

Optimising the anaglyph technique to study ancient and forensic bloodstains

Anaglyphy is a stereoscopic technique based on the superimposition of two images of the same view, taken from slightly different angles as well as in two different colours. This superimposition produces a depth effect when viewed through glasses having one red and one green, blue or cyan lens acting as a colour filter. A study (reported in the journal Micron, vol. 40 (3), pp. 409–412), carried out by Policarp Hortolà, senior researcher & lecturer of the Rovira i Virgili University, and collaborator of Catalan Institute of Human Palaeoecology and Social Evolution (IPHES), has shown that digital anaglyphy provides a simple and feasible method to improve the relief effect of SEM micrographs of bloodstains.

Anaglyph obtained from two SEM micrographs of a human bloodstain. Suitable 3D glasses must be used for a correct viewing of the image

First, a chert fragment was smeared with human blood. Then, the specimen was coated with gold and examined via secondary electrons by a scanning electron microscope (SEM). After obtaining SEM micrographs, anaglyphs were digitally generated using a free software for making anaglyphs and other 3D images. The best results were obtained using pairs of SEM micrographs acquired at 10° differing angle and at SEM-stage tilts that were symmetric from the horizontal plane. The relief effect was more accentuated at low magnification. The most ergonomic colour combination for viewing bloodstain anaglyphs was red–cyan.

As a first consequence of this improvement, the results obtained in this study revealed that the outermost erythrocyte layer of a thin bloodstain – coinciding, in general, with the smear surface – can be much more uneven than that previously suggested by customary SEM micrographs.

For more information:

Article "Using digital anaglyphy to improve the relief effect of SEM micrographs of bloodstains"

Micron, 40: 409-412


Policarp Hortolà

Area of Prehistory (Rovira i Virgili University) & Catalan Institute of Human Palaeoecology and Social Evolution (IPHES)

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