RTI processing tutorial:
Greg takes you step by step through the process of transforming your photos into an RTI image.
Week 2 Overview (July 20th, 2012):
Our second week of the project ends today. On Monday the project team traveled back to O’Keeffe’s home in Abiquiu for photogrammetry capture. Dale wanted to capture a section of the exterior adobe wall. It was mid-day and the wall he originally wanted to capture was facing a garden with large bushes and a tree. The tree was casting too many shadows on the wall and there was a slight breeze. The team did not know how this would affect image processing within PhotoScan so we moved to an alternative wall without any direct shadows laying upon it (besides some plants and a ladder).
There was also a large, recently watered garden between the camera and the wall so a 100mm lens was needed. The team positioned the camera 42ft away from the wall so that it would be fully within the frame. Ideally the camera would have been closer to the wall, but certain obstacles, such as the moist soil, forced us further back than we would have liked.
To keep the front two legs of the tripod at a constant 42ft from the wall, a chalk line was used as a guide. This enabled the team to maneuver the camera horizontally and still keep accurate distance from the wall.
Along our horizontal line, a large bush sat within our line of sight. To fix this problem, we shot at a 15 degree angle outside of the bush to capture the wall the bush was blocking; PhotoScan had no problem putting the 3D image together.
After all the images were captured horizontally, 90 degrees and 270 degrees they were ready to be processed in PhotoScan.
Much of the detail was lost, probably from being too far from the wall, but the mesh was mostly clear. Some of the areas where we had plants against the wall are distorted.
Point Cloud View:
Throughout the week we completed additional RTI’s of three paintings “Easter Sunrise”, “Pedernal”, and “Mesa and Road East” The continuous practice of RTI makes the process faster and smoother.
Week 2 Photogrammetry:
July 12, 2012
Two characteristics of our project are especially important. First, it is important to us that the entire process is scientific, i.e. transparent, documented, replicable and aligned with ISO, AIC, ICOM photographic documentation standards. To this point, the entire sequence, from capture to computational image is open format, non-proprietary and open source. The metadata and computational pathway of each pixel is readable, documented, archival and can be assembled into a 3D computational image at any time in the future using whatever developments in normal reflection or photogrammetry software and camera hardware occur. To fulfill the scientific requirements of photo documentation in conservation and preservation, 3D or otherwise, there can be NO proprietary files or software conversions and the owner of the initial capture needs to own and archive all workflows using a metadata “lab notebook”. No steps can be hidden.
Second, we are principally aiming to develop reliable protocols for 3D, photogrammetrically accurate images using a CONSUMER GRADE DIGITAL CAMERAS, rather than expensive and complex laser scanning technologies. If reliable workflows can be defined, ANYONE with a digital camera with a manual mode setting, raw capture capability, and a flash and a laptop computer may be able to gather RGB color and 3-D data and assemble 3D digital surrogates that can be used to monitor very slight condition changes that occur over a very long period of time.
On the LinkedIn Group Heritage Conservation/Historic Preservation of the Built Environment Network, Graham U’ren, a trustee at Built Environment Forum Scotland, posted a comment noting the visually exciting and richly detailed Scottish Ten project, an “ambitious five year project using cutting edge technology to create exceptionally accurate digital models of Scotland’s five UNESCO designated World Heritage Sites”. The Scottish Ten project is partnering with CyArk a 501C3 non profit who uses their proprietary software to build and store 3D image files from laser-scanning point-clouds. They use highly precise, high speed terrestrial laser scanning systems, some capable of sub-millimetre data capture and aerial optical remote sensing technology. Visit their project website at http://www.scottishten.org/
Monday, June 25, 2012 begins a new, 8-week, O’Keeffe Museum Conservation Program summer preservation project. This year, thanks to the generous financial support of the National Center For Preservation Technology and Training (http://ncptt.nps.gov/ ), The Stockman Family Foundation and New Mexico AmeriCorps Cultural Technology community service program, we will be testing three, exciting, new technologies in “Computational Imaging”.
In conservation and preservation, computational imaging uses the power of today’s laptop microprocessors and digital cameras to create accurate, archival, 3-D images and documentation for artistic and cultural objects. From the microscopic texture of a paint brush-stroke to the undulating pitch and volume of a historic adobe wall, computational imaging can document and help monitor the changes in three-dimensional shape, size and deterioration of the historic properties and objects under the care of the Georgia O’Keeffe Museum. Since we preserve, document and monitor everything from historic landscapes and historic structures to O’Keeffe’s paintings, pastels and drawings to the tiny snail and scallop shells she collected and imaged in her art, automating and increasing the accuracy of our documentation and measurements can help us get better work done, more systematically, and in less time.
New Mexico AmeriCorps Cultural Technology (NM-ACT) interns Joey Montoya of Espanola and Greg Williamson of Santa Fe will join Head of Conservation Dale Kronkright and Assistant Registrar Darrah Wills in testing three imaging processes: Reflectance Transformation Imaging, Stereo Photogrammetry and Structured Light Imaging. Each uses different algorithms to construct detailed 3-D images and data by assembling regular, 2-D digital photographs.
To make the documentation useful from a scientific perspective, the source photographic conditions, resolution and algorithmic processing pathways must be carefully documented in a digital “lab notebook”. Further, to facilitate the accurate computer comparison of 3-D features of a painting, door, window or landscape over time – to determine if features are subtly changing in ways that indicate underlying deterioration or damage – the algorithms must be able to recognize and compare L*A*B* feature data in photographs that have been taken years or decades later with different cameras, different lighting conditions and slightly different orientations. These conditions are pretty demanding!
Week 1 Overview (June 29th, 2012)
Dale Kronkright scheduled Mark Mudge and Carla Schroer from Cultural Heritage Imaging to spend a week training staff on Computational Imaging. Cultural Heritage Imaging’s ambition is to make digital imaging methods more utilized to preserve and monitor cultural artifacts.
Mark and Carla trained us in two methods of Computational Imaging. The first being Reflectance Transformation Imaging (RTI) and the second Stereoscopic Photogrammetry. The first day was primarily explanation of theory and how the software processed the images.
Several days were spent training RTI and how to shoot ideal images. Our speed and placement of the flash progressed after each attempt. First we shot O’Keeffe’s painting “Untitled (Cottonwood Tree)” and “Horn and Feathers.” However, “Horn and Feathers” was also shot in infrared.
After processing the images in RTIBuilder, detailed texture the human eye cannot see was made clearly visible. “Soap bubble’s,” due to humidity changes, were also made clear. In the infrared RTI image Dale was able to point out the underdrawing of O’Keeffe’s painting.
Toward the end of the training we travelled to O’Keeffe’s home in Abiquiu where we did more Photogrammetry and RTI imaging.
Overall, week 1 turned out to be very successful. CHI prepared us to continue capturing images throughout these 8 weeks and we will continue to post updates on our progress.
Week 1 (June 29, 2012):
We completed our first week of intensive training on June 29th. The first day we learned the theory and technique behind two methods of Computational Imaging: Reflectance Transformation Imaging (RTI) and Photogrammetry. Being unfamiliar with the two methods it was easy to grasp the concept but difficult to grasp how it processed. The first few days we worked primarily with RTI and how to process the images in the software. Equipment for these methods are extensive so it will take several attempts to be familiarized with them and how to set up. When the equipment was being introduced to us I was slightly overwhelmed because I was unfamiliar with most of it; it became more clear after using it once or twice. In this case learning is by doing.
We ran into some initial issues when beginning RTI. The new Canon 5D camera had an issue and had trouble communicating with the computer. After several attempts we had to switch to Mark and Carla’s camera. It worked the following day without explanation so it was a minor hiccup. Our first RTI came out successful. Since we are mimicking a dome, we spent some time trying to get the flash to the correct position. As we continued practicing, visualizing each angle became easier and much quicker.
Since there is so much equipment and things to keep track of for RTI, minor hiccups can stall a shoot from a few minutes to several hours. Batteries not being fully charged or camera malfunctions will take up time. The process will take more time than originally anticipated so some flexibility is necessary. If software or equipment is not working properly, begin with making sure all connections are stable and connected properly. After that one can start troubleshooting each individual piece of equipment from the top down. And a very important reminder is to be aware of your surroundings at all times. One bump on the tripod will result in a re-shoot. Luckily we haven’t ran into that issue yet.
Another time while doing RTI, after setting the focus, we forgot to set the focus to manual on the camera. The camera ended up changing focus right before the shoot without our knowledge. After several shots we realized the change and had to start over. One should check the focus again immediately before shooting to avoid a re-shoot.
Photogrammetry uses a separate software than that of RTI. On our Photogrammetry test we were being extremely precise on camera placement by using measurements. A chalk line or measuring tape makes the process quicker so that one can visualize distance between the subject. Our attempts at being extremely precise were taking up a lot of time, but in reality the software still manages to recognize familiar points and string them together. We had to be precise in our distance from the subject but not by the centimeter. One can successfully do Photogrammetry without a tripod, moving laterally along a chalk line. It took several long attempts to come to that conclusion.
As Mark and Carla warned us in the beginning of training, its a fire hose of information. There is lots of terminology and lots of equipment to interface with. We were able to get some great equipment troubleshooting tips from Carla and Mark during this first week because there were plenty of equipment problems. There is nothing better for familiarizing oneself with a piece of equipment than attempting to fix it when it is malfunctioning.
As for training, It is hard to visualize the angles the flash needs to take in the RTI capture process. We are told to picture an umbrella that surrounds the artwork that the camera flash has to follow. This visualization requires practice. It would be of tremendous help if there was some type of visual guide. Very steep learning curve, with software, equipment, techniques, do’s don’t, and art safety. The huge payoff was the creation of our first successful RTI image with an Okeeffe painting and an image of the front of the research center here in Santa Fe captured using photogrammetry.
What I learned from our field work is this…mosquitos stink! Bring suntan lotion and bug repellant when doing field work. Setting up is 90% of time taken in RTI and Photogrammetry. Organization is essential with equipment in specific bags, and labeled. Makes packing up and setting up easier and increases efficiency by a huge factor.
Hello, I am a computer science major at New Mexico Highlands University. I am lucky enough to be working on this project through the Americorps Cultural Technology program.
I was born in Carlsbad, New Mexico and appreciate Okeeffe’s appreciation of the New Mexican landscape. I received my undergraduate degree at the University of New Mexico with a degree in classical guitar performance. I have gone from pumping nylon all day to banging away at a keyboard. I hope you enjoy the site, we have had a lot of fun making it.