RTI Guide to Highlight Image Capture

Rti Guide To Highlight Image Capture-Free PDF

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Reflectance Transformation Imaging Guide to Highlight Image Capture v2 0. 2013 Cultural Heritage Imaging All rights reserved. This work is licensed under the Creative Commons Attribution Noncommercial No Derivative Works 3 0. United States License, To view a copy of this license visit http creativecommons org licenses by nc nd 3 0 us. or send a letter to Creative Commons 171 Second Street Suite 300 San Francisco California 94105 USA. Attribution should be made to Cultural Heritage Imaging http CulturalHeritageImaging org. Documents are also available in Spanish translation see http CulturalHeritageImaging org downloads. Acknowledgments, The methodology described here was developed at Cultural Heritage Imaging by Mark Mudge Marlin. Lum and Carla Schroer with technical guidance from Tom Malzbender of Hewlett Packard Labs The idea. for Highlight RTI and its original execution was a collaboration between Tom Malzbender Mark Mudge. Marlin Lum and Carla Schroer Many others commented tweaked gave ideas and were generally helpful. in the development of the capture methodology and this guide It is impossible to name everyone who. contributed but we would especially like to acknowledge Professor James Davis at UC Santa Cruz and our. Portuguese collaborators at the University of Minho Alberto Proen a Luis Paolo Santos and Jo o Barbosa. Version 1 of this guide was funded in part by a grant from the National Park Service and the National. Center for Preservation Technology and Training Version 2 of this guide was funded in large part by the. Institute of Museum and Library Services 21st Century Museum Professionals Grant IMLS Grant. MP 00 10 0031 10, The contents are solely the responsibility of the authors and do not necessarily represent the official. position or policies of the National Park Service or of the National Center for Preservation Technology and. Training or of the Institute of Museum and Library Services. Additional funding was provided by charitable contributions to Cultural Heritage Imaging. Special thanks to Judy Bogart of Expert Support Inc for donating her time and expertise in the. development and writing of this guide,Setting up for Highlight RTI Image Capture. Highlight RTI image capture is a technique for obtaining the original digital image data from which you. can produce reflectance transformation images RTIs An RTI in addition to storing the color data for each. pixel stores a normal value for each pixel that records its surface shape The processing software calculates. this value using data about the position of the light in each image relative to the camera. In highlight RTI image capture technique you include one or preferably two reflective spheres in each. shot The reflection of the light source on the spheres enables the processing software to calculate the. light direction for that image This allows you great flexibility in subject size and location. Physical setup summary, It is very important that the camera the target object and the reflective spheres do not move at all during.
the capture sequence only the light moves,You need to set up the following elements. You must set the digital camera on a tripod or camera stand for stability and to eliminate vibration. during image capture Sandbags or other weights can help you to further stabilize tripods and. We use Canon digital SLRs for illustration and demonstration but many different camera types have. produced high quality RTIs You must be able to set exposure and aperture manually and turn off. autofocus in order to keep a fixed focus on the subject. The recommended method is to connect the camera to the computer and use the computer to. control it for testing your setup and when shooting the images This way you can trigger the camera. and flash directly from the computer and download and name your images at the time of capture. Alternatively you can use a remote triggering device for the camera such as a trigger release cable or. radio trigger,For details see Camera setup on page 6. Target object with reflecting spheres, Depending on the size and portability of the target object you must compose the camera s field of. view so it can encompass both the object and two reflecting spheres of an appropriate size The. spheres should have a diameter of at least 250 pixels in the resulting photograph. There are various ways to mount the reflecting spheres In general you can set the spheres on stands. in the target area or mount them on light stands or tripods to get them into the desired positions. For details see Subject and reflective sphere setup on page 11. Setting up for Highlight RTI Image Capture Overview 4. You must have a portable lighting unit of a type and intensity appropriate to the location and. environmental conditions For this technique you can attach the lighting unit to a pole or monopod. and move it by hand into the general positions required for a complete set of images in an imaginary. hemisphere around the subject, The distance of the light from the object must be the same for all shots you can easily measure it with. For details see Lighting setup on page 17, If you are using a computer to control the camera it must be near enough to connect and be easily.
accessible but it must be placed out of the way of the object camera and lighting area You can. mount it on any stable surface In outdoor field situations it is useful to mount it on another tripod. stabilized by weights or sandbags, Connect the camera to the computer through a USB cable as shown in Camera setup on page 6 and. install the camera control application for your camera see Computer software setup optional on. page 22 You must also install the capture and post processing software that we provide and the. viewer application that allows you to view your RTI images See Computer software setup optional. on page 22,camera mounted to face down,wireless transceiver to. trigger light source,computer on tripod,weight for stability. target with object and,black spheres,cable wrapped. around leg to avoid,light wand, Setting up for Highlight RTI Image Capture Overview 5.
Starter Kit, For convenience Cultural Heritage Imaging offers an RTI Highlight Capture Starter Kit that is designed to. get you up and running quickly It contains all the parts you need to capture images for RTI using the. highlight method, For complete details see http culturalheritageimaging org rti kit. CHI Forums, As a public service Cultural Heritage Imaging hosts and maintains a set of online forums intended for the. community of users developers and others interested in Reflectance Transformation Imaging RTI. Algorithmic Rendering and related computational photography techniques. In order to post in the forums you must sign up for and verify an account but there are no fees or other. requirements for membership Except for the Announcements section posts are not moderated but CHI. staff monitors the forums and warns users who post inappropriately. You can see a short description of the existing topic areas here. http forums culturalheritageimaging org, We welcome suggestions for additional topic areas If you have private comments or suggestions send. e mail to forums c h i org, Setting up for Highlight RTI Image Capture Camera setup 6.
Camera setup, You must set the digital camera on a tripod or camera stand for stability it is very important that there be. no movement or vibration of either the camera or subject You can mount the camera directly on the ball. head mounted on the top of the tripod or at the bottom of the central column. There are many possible configurations depending on the size portability and positioning of the target. object Some possibilities are shown in these illustrations. Mounting the camera, Before you mount the camera attach the lens and any filters you are planning to use. You can mount the camera directly on a ball head on the tripod or you can attach a plate to the camera. and attach that to a clamp that you mount on the ball head as shown here The plate and clamp setup. can make it easier to mount and unmount the camera and it can also make the camera more stable. Plate attached to camera,and mounted on a clamp,that is attached to the ball. head on the tripod, Setting up for Highlight RTI Image Capture Camera setup 7. You can attach the camera to a ball head on top of the tripod for a vertical capture position for paintings. hanging on a wall for instance or you can attach the ball head and camera to the lower end of the tripod. central column see Choosing a configuration on page 8. Here the camera is mounted on the ball head on top of the tripod. bubble level,radio transmitter,or transceiver,USB cable to.
The radio transmitter shown here is optional see Flash lighting options on page 18. The USB cable attaches the camera to the computer see Connecting the computer and lights on. Setting up for Highlight RTI Image Capture Camera setup 8. Choosing a configuration, Configuring the camera and tripod depends on the size and portability of the target object as well as what. equipment you have available Line up the plane of the camera to be parallel with the plane of the subject. or subject detail you wish to photograph,Vertical subject. To shoot a vertical subject such as rock art or a painting hanging on a wall mount the camera on a ball. head on top of the tripod facing the subject,Horizontal subject. To shoot a subject that is on a horizontal surface mount the camera so that it views the subject from. directly above, Generally the best choice for a horizontal subject is to mount a ball head upside down on the bottom of. the tripod s central column and rotate it so that the lens faces straight down This creates the fewest. shadows and makes positioning easier, Setting up for Highlight RTI Image Capture Camera setup 9.
Camera attached to ball head fixed to,bottom of central column of tripod. facing down, For larger objects use a larger tripod If the subject is too large for available tripods you may need an. alternative camera support such as a cross bar supported at both ends with an attached camera clamp or. ball head The crossbar must be long enough so that the shadows from the cross bar supports are not a. These cameras are mounted facing directly down onto the target object and spheres. Floor mount camera stand,Table top copy stand, Setting up for Highlight RTI Image Capture Camera setup 10. Always choose a configuration and position that minimizes any shadows cast from the tripod legs onto the. subject at any of the lighting angles, If you find that you cannot avoid shadows at some lighting angles do not shoot at those angles If you get. shadows on areas of interest in any of the images from objects outside the target object such as tripod. legs or spheres discard those images during post processing Be careful to distinguish such shadows. from those that a sculptural object might cast on itself. Connecting the computer and lights, When the camera is approximately positioned set the computer near the camera and connect the camera.
to the computer with the USB computer control cable We recommend using the computer to control the. camera settings and trigger the shutter and lights in order to prevent any camera movement. Alternatively you can use a remote trigger see Triggering trade offs on page 30. If you are using a flash configure the camera to make sure that the camera s shutter synchronizes with the. flash see Lighting setup on page 17, To finalize the camera position you must adjust the relative positions of camera and subject in order to. frame the subject correctly in the camera s view as discussed in Setting up the capture session on. Stabilizing the camera assembly, It is essential that the camera not move at all during shooting Set the tripod legs as wide apart as. necessary to prevent shadows but make every effort to maximize stability When you have framed the. subject correctly in the camera s view tighten all the clamps and mounting screws Once everything is. correctly framed you should adjust nothing but the camera focus. Always use remote triggering of the camera shutter You can use the camera control software to trigger. the shutter see Computer software setup optional on page 22 or you can use a remote shutter. release If you use a remote shutter release it can be wireless or wired Wireless is preferred but if you must. use a wire or cable release make sure the wire or cable is securely attached to something stable and out of. the way so that shutter release causes no movement or vibration. Use weights to stabilize the camera assembly and eliminate all movement and vibration. Drape sandbags over the tripod legs when they are widely separated. If the camera is mounted on top of the tripod you can hang a weight from a center column hook. inserted in the bottom of the tripod shaft This is very good for stabilizing the weight of a large. You can also use weights around the feet of the tripod particularly in an outdoor environment. Setting up for Highlight RTI Image Capture Subject and reflective sphere setup 11. stabilizing sandbag on tripod leg,sandbags mounted on center. column of tripods to stabilize,both camera and computer. Subject and reflective sphere setup, Use a neutral background colored backgrounds can reflect their color onto the subject Try to use a white.
black or gray neutral background as appropriate for contrast with the target object If the subject is. Reflectance Transformation Imaging Guide to Highlight Image Capture v2 0 only the light moves You need to set up the following elements Camera You must set the digital camera on a tripod or camera stand for stability and to eliminate vibration during image capture Sandbags or other weights can help you to further stabilize tripods and supports We use Canon digital SLRs for

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