Using DSLR to 'Scan' Colour Slides: learning from the Digitising Jemdet Nasr 1988–1989 Project

This article presents a cost-effective method for digitising photographic film for archival purposes using a DSLR camera, focussing on the widely used colour reversal Kodachrome film produced by Eastman Kodak between 1935 and 2009. I discuss the digitisation of an archive of 787 Kodachrome slides taken between 1988 and 1989 during the excavation of Jemdet Nasr, an archaeological site located in southern Iraq (Project website). I compare results obtained using a film scanner (Nikon Coolscan IV ED) with two different scanning software solutions (SilverFast and VueScan), a flatbed scanner (HP Scanjet 8300), and two DSLR cameras with macro lens (a Canon EOS KissX3 with 105mm lens and a Canon EOS 80D with 90mm lens). The results demonstrate the cost-effective value of the DSLR method for archives where time and resources are limited, but where digital photography equipment might be readily available, such as an archaeological unit or a university department. The method allows for high quality, fast and economical digitisation of excavation and collection archives that will enhance research. The method also offers superior results in rendering the high dynamic range of photographic film such as Kodachrome.

QUICK DETERMINATION OF CRYSTAL SIZE DISTRIBUTIONS OF ROCKS BY MEANS OF A COLOR SCANNER

An acquisition and analysis method based on a commercial, low-cost, high-resolution film scanner is presented. It allows to collect data from standard rock thin sections with a resolution up to 9.4 μm per pixel. Common and general purpose facilities (scanner + PC + image analysis software) may thus be transformed in an appropriate tool for quantitative textural analysis of rocks. The procedure implies the acquisition of four images with crossed polarizers and one parallel light image. Crystal boundaries are extracted from fields in crossed polarizers, while markers for mineral recognition are obtained thresholding the parallel light image. The method is tested for fresh rocks with simple mineralogy (harzburgites and marbles) with no more than three phases, all exhibiting well distinct optical properties. Image processing is performed developing procedures with VISILOG 5.2 package. 2-D size data from binary images are converted to 3-D size data applying stereological corrections. 3-D data are reported in bi-logarithmic diagrams, plotting the crystal number density versus characteristic lengths. The harzburgite samples show a scale invariance of size distributions of olivine while mosaic equant marbles exhibit a different size distribution pattern, without scale invariance and a relative maximum.