Alternative uses for Pre-Process Masking

In the following two examples, a Concrete Mix block (Figure 4.43) and a Sea Shell (Figure 4.44), both items which had been placed on the turn table, needed additional support so as to photograph them in the best possible positions, so as to record as much data as possible. This support was provided by thin wooded sticks as seen in Figures 4.43 and 4.44. Both were photographed in an upright position with a supporting wooden stick pushed, as in Figure 4.44, into the shell, or as in Figure 4.43, supporting the back of the concrete block. Both images, Figure 4.43 and Figure 4.45, are from the data sets of images which were then masked, as described above, before being processed by the software. Masking frames are used by the software to build the final 3D images.

137 Figure 4.44: Original image of

Sea Shell.

Figure 4.45: Positive masked over sea shell support.

By examining the virtual point cloud image at each stage of processing, of which there were four, the possibility of elimination of part of the newly created point cloud virtual image was possible. Having removed the pixels, the software proceeded to the completion stage.

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Figures 4.45 and 4.46 show the original images having been masked, the positive and negative of the same image are shown. In the first of these images, the support can just be seen (indicated), in the negative/reverse image the wooden stick has been completely eliminated and only the cutout on the base of the shell are seen, the entry points to the shell are arrowed. The last image is of the final textured Sea Shell without the supporting wooden stick (Figure 4.47). The Concrete Mix block has been treated in much the same way except the masking of the wooden sticks cuts out data from the digital image (Figure 4.48).

Figure 4.48: Positive mask image of Concrete Mix.

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However, as can be seen from Figure 4.49, the software has compensated for this lack of data and the stones merge in to fill the void left by the masked out wooden sticks. Although the orientations of both of these images are not identical, in the center of Figure 4.48, it is possible to identify and match some of the larger stones onto the image on Figure 4.49.

The oldest and most valuable artifacts to be photographed and replicated using the light tent method were from The Kendal museum collection which was established in 1796, as a ‘Cabinet of Curiosities’.

Figure 4.50: Sobekhotep seen in center of light tent on turn table.

Three objects from the collection were initially chosen: a small bowl, approximately 120mm diameter and 45mm high (Figure 4.31), a vase 120mm high and 100mm diameter (Figure 4.42) and a statuette of Sobekhotep, son of Nehesy10, approximately 200mm high. In Figure 4.50, is the limestone figure of Sobekhotep (from the second Intermediate Period, Abydos, Tomb 537A’08, which dates to around 1500BC, and was a very important and rare figurine within the Kendal museum collection) on the turntable ready to be photographed. “This is a very important and rare figurine which represents Sobekhotep, son of Nehesy, an official who lived at Abydos during the Second Intermediate Period. The figure is somewhat crude, showing Sobekhotep wearing a round wig and a kilt, standing with the left foot forward, and has been carefully painted. The back

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pillar preserves a hieroglyphic inscription, which shows that Sobekhotep's sister Kemet gave the statuette of her brother as an offering to the god Ptah-Sokar- Osiris:

“A boon which the king gives (on behalf of) Ptah-Sokar-Osiris, that he may give offerings to the Ka of ... Sobekhotep the justified, begotten of Nehesy, by his sister who causes his name to live ... Kemet” (Snape 1994: 310).

Sobekhotep may have been a soldier, and so his sister may have dedicated the statue of her brother after he died in active service and was buried at Abydos (Snape 1994: 312) [75].

Figure 4.51: Screen shots of masked images and view of camera positions. The method of geometric data capture was the same for all these items. In the case of Sobekhotep, the maximum amount of detail was required not just in the silhouette but also of the hieroglyphics that had been written down the sides. The camera was positioned in one of four elevations, for each data set, being higher, lower or on the same plane as the subject being photographed at elevations of 20° to 30° to the horizontal. This ensured that every part of the object was recorded and that a good overlap of images was obtained, the artifact being in the centre always at the same elevation.

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In Figure 4.50, the camera can be seen close up to the subject, depending on the artifact’s size, allowing for small objects to be photographed. If necessary a close up lens could be fitted. For each object on the turn table, a rotation of 10° would produce 144 images, but if more detail was thought to be required an extra 10 images would not increase the processing time significantly. On the other hand a simpler artifact needing less digital information might have been rotated only 15°, producing up to 96 images, also allowing for a few extra shots if thought necessary.

Figure 4.52: Photograph of Sobekhotep, son ofNehesy.

Figure 4.53: Sobekhotep – High resolution point cloud image. Being nearer the subject, the focusing and the DoF became far more important, increasing criticality of the focusing. As the lens moved closer to the subject, the shallower the DoF became but by increasing the f/stop to f/18 or f/22+ this problem was overcome, however one must be aware that at such small apertures there is the possibility of a loss of image sharpness due to diffraction. At this small aperture increased illumination on the artifact or a longer time exposure is required. Although the images seen in Figure 4.51 are the masked

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negatives, the subject matter, Sobekhotep, filled each frame. The images in the frames were not cropped or altered in any way as to do so would confuse the software in the processing stage and distort the stitching process. The detail that is shown in Figure 4.52, an original photograph, can be seen quite clearly in the final processed screenshot of the high resolution digital images (Figures 4.53and 4.54). The file of this image, a *.obj file, was now ready to import into StudioPro®

to produce the *.stl file required for the non-colour AM machine. If colour printing had been available the file would have been imported into DeskArts’ 3Data Expert® to produce the *.wri file.

Figure4.54: Sobekhotep - Enlarged detail of high resolution image.

4.10.2 Digital Photographs, Point Cloud and Polygon Images