Since first posting about the images of the Four Evangelists found on the medieval cross-base at Gulval Church, I have been striving to produce clearer images of each saint for inclusion in a publication. The image will only ever be as good as the condition of the stone allows, but it is possible to wring a fair amount of detail from the monument through digital means.

The most difficult image of the Evangelists on the Gulval stone is St John. Depicted as half man, half eagle, his side of the cross base is damaged and worn, especially at the top. The details which I would like to further enhance are the eagle head, and the book he is holding in his hand. This is the only side where the lettering is far from clear, and many people remain to be convinced that there is indeed an “IH” (Iohan) carved on it at all.

As many archaeologists do, I have become rather obsessed with this image. When processing data of this nature one does have to be very careful in the interpretation, and not see what one wants to see. Part of my ‘therapy’, if you like, is to blog about the results as I go.

So, I have re-processed the photographs of the east side of the cross-base using the highest level of detail that my computers will allow, adding in some extra angles which I did not use in my initial images, to try and capture further detail at the sculpture’s head level. The processing took from about 7am until 6pm. After some tidying of the data (and a fair amount of quiet wishing that the computer wouldn’t crash), I produced a 1.7GB point cloud ready to inspect.

The use of false colour can be really useful, as it affects one’s perceptions of the data. Good for ‘getting your eye in’ to the data, and the shapes of the carving.

So without further ado, here are some renderings of St John with his Symbol’s head (the eagle). Can you spot any vertical lettering on his book? Fellow digital specialists please note that this is still rough data!

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High contrast ambient occlusion.

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Greyscale ambient occlusion.

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Ambient occlusion using red and yellow colouring

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Ambient occlusion using red and white colouring.