Sunday 6 January 2013

Infra-red Photography

Last Week I attended Digidoc conference in Edinburgh (http://www.digitaldocumentation.co.uk/) and met a fellow PhD student Kieran Baxter who is looking the use of at Kite Photography to record archaeological sites. His website is here: http://www.topofly.com/ He mentioned that several archaeologists he knows of have experimented with using infra-red cameras when taking kite photographs. Having recently attended a lecture by Stuart Laidlaw at UCL http://www.ucl.ac.uk/archaeology/calendar/articles/20121015 that described the conversion of digital cameras to take infra-red images I decided to try it out on an old camera. I have an Olympus sp-350, which turns out to be a very suitable camera for conversion. There are instructions here for a variety of digital cameras: http://www.scaredycatfilms.com/digicam_mods/index.html All digital camera sensors can record infra-red light, but they are fitted with a filter to block it out- so you have to open up the camera and remove the filter. This is my first image with the filter removed. It is out of focus because the filter is used to correctly focus the image. I was very excited to see that the ivy shows up as red. The second image shows the same scene on my NEX-7

Infra-red filter removed Visible light only

In order to block out normal visible light you have to replace the filter. As yet I don't have a proper visible light filter, but the scardycatfilms website suggested using a piece of exposed negative. I combined this with two pieces of clear plastic to make up the same thickness as the original filter (to re-establish the correct focus). The results look like this:
















and a little bit of playing with Photoshop filters (the original was a raw image) pulls out the vegetation from the rest of the scene:


  In order to try out the filter properly I cycled out into the countryside and took some very nice, slightly spooky images as shown below. Infra-red light makes a useful addition to the archaeologists toolbox when reading satellite images, so I think it would be useful to try out some infra-red kite photos and see if I can integrate them with a sfm pointcloud.











 some links: http://www.armadale.org.uk/phototech05.htm http://www.academia.edu/1155568/Near-InfraRed_Aerial_Crop_Mark_Archaeology_From_Its_Historical_Use_to_Current_Digital_Implementations Geert Verhoeven

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