In this video we will cover how to capture reflectance transformation images using the highlight method.
Transcript: In preparing for a capture session, be sure to go through the Setup for Image Capture Checklist and the Guide to Highlight Image Capture, both available from the Cultural Heritage Imaging website,
RTI's are created by combining the data from many images that are taken in a sequence. RTI's use the actual surface information from the object that you will capture with the highlight technique covered in this video.
To create an image sequence, you take pictures from various sampling positions in an imaginary dome around the object. Imagine that the dome is like an umbrella, in which each rib extends from the center of the camera lens.
Pictured here is an RTI lighting array. The highlight technique effectively reproduces the sequence captured by this highly precise device. There should be 8-12 ribs. The ribs should be at equal distances from one another.
Along each rib you should take 3-6 shots, depending on the desired quality. Take the shots from the outermost point on each rib and move inward to assure coverage and distancing. As you take your shots, it's essential that the center of the cone of light from the flash point directly at the subject and remain parallel to the string.
Keep taking shots until you complete the sequence, then move on to the next rib. If the camera misfires or the flash does not go off or some other shooting error occurs, make a note of it in your documentation and retake the picture.
This is an animation of the highlights captured on one of the black spheres. Note how the highlights move in lines inward approximately on each rib. During processing, the RTI software will produce a highlight map, so you can see exactly the coverage you achieved in your capture session.
You should begin by measuring out the virtual dome. We recommend starting with the highest rib position, and move inward from there. Position the flash so that the center of the cone of light points directly at the subject and remains parallel to the string.
When the position is established, move the string out of the shot and take the picture. Continue taking image samples along each rib. the string holder should watch to be sure the flash is pointed correctly, and the flash holder should audibly call out 'go' to the camera operator. Notice how all three team members pay attention to the scene to assure that no mistakes are made, such as bumping the tripod, black spheres or object.
If the flash fails to fire, communicate with the camera operator who should document the problem, then retake the shot from the same position. After completing the sequence from one side of the camera, carefully move to the other side to finish taking your samples.
Depending on the RTI result your are aiming for, you should have successfully taken 36-60 samples.
Congratulations! You have completed your highlight RTI capture session!
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