Figure: Lighting dome with camera and initial light fixings.
In order to fully test whether PTM would be an effective method for recording the the surface texture of paintings, suitable equipment was required. A system capable of reproducibly lighting a painting from many different direction was required.
Initially a test target was mounted on an easel in a photographic studio, in front of a digital camera. A set of images was then taken using only one photograph light. For each image the light was carefully placed and its position relative to the center of the painting was measured.
This process took quite so time, but the resultant images were successfull combined to form a PTM. Even with the limitations imposed on the positioning of the lights, with this system, the resultant PTM showed definite promise, so worked progressed to produce a more controlable and reproducible system.
The example imaging system shown on the HP lab PTM web page was based on a dome structure, so a similar system was used.
With this first prototype system it was decided to keep the system reasonable small, large enough to examine paintings not much bigger than the size on an A4 piece of paper.
A dome structure based on four octagons was built, with a central mounting for a Nikon Coolpics-995 digital camera. 24 small, low voltage, spot lights were then secured to the dome structure and directed towards the central point. Details of light fixings and camera mounting can be seen in the figures below. At this stage the lights were turned on by connecting then directly to the power supply.
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Figure: Lighting dome with camera and initial light fixings. |
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Figure: Details: A: Construction of Light fixings. B: Mounting point for the Nikon Coolpics Camera. C: Power source for lights. |
Several test samples were then examined using the system and the results achieved were very encouraging. The next stage was to improve the process by which the lights were controlled by adding a switching mechanism.
In order to improve the method for turning each of the lights on/off, the lights were all wired up and connected to a control box. The control box was constructed to allow the selection of any individual light, first by choosing which row of lights (1-3) and then which of the lights within that row (1-8) to actually use.
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Figure: Two views of the lighting dome, wired up and connected to control box. |
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Figure: Detail of the Control Box: A: Front view. B: Rear view and C: View on inside of control box. |
The Dome was then further developed to minimise internal reflections. The inside edges were painted black and small matt black covers were placed over the light reflectors when they where not in use.
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Figure: Two views of the lighting dome, wired up and connected to control box. |