Using digital anaglyphy to improve the relief effect of SEM micrographs of 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. The nearly flat surface of a chip of grey chert was thin-smeared with peripheral human blood. Two months later, the specimen was fixed to a microscope stub as horizontal as possible, coated with gold, and examined via secondary electrons by a scanning electron microscope (SEM). After obtaining SEM micrographs, anaglyphs were digitally generated. 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. Digital anaglyphy provides a simple and feasible method to improve the relief effect of SEM micrographs of bloodstains. Moreover, as a first consequence of this improvement, the results obtained in this research reveal 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.