RTI Reflectance Transformation Imaging: tips and tricks

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This blog is a brief intro to RTI (Reflectance Transformation Imaging) and my personal tips and tricks. You find everything on the website of the group developing the tool.

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Reflectance Transformation Imaging, RTI, paintings authentication, Technical Art Examination

Painting is ready for Reflectance Transformation Imaging Documentation. The set up is extremely simple, a black ball and a color checker – AIC PhD Target.

I must say I was not that excited the first time I heard about it while I was fellow in conservation science at the Metropolitan Museum in NY in 2010. There was an RTI training section and yes, I thought it was a kind of enhanced-raking light-Photoshop method.  Though, after testing it myself, I have been captured by the fact that it produces an actually useful documentation with basic equipment and pretty fast and simple procedure. I find RTI especially useful for my work in support for appraisal and authentication professionals. When you want to share the “feeling” of the painting’s surface with the team you are working with – but they are scattered around the world and you are the only one who has access  to see the painting.

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What you need. I have to do Reflectance Transformation Imaging  – RTI –  all alone with as a light equipment as I can. So this is what I figured out.

  • Camera.  I recommend an high-resolution camera. Since stitching photos to get bigger images is not an option here (you should do the same stitching at least 24 times!!) you should use a camera with pixel count enough to get the details you need. I use my beloved Nikon D800, 36 MP.
  • Black Spheres. You can be creative and try to experiment using everything you find suitable. I have used black marbles (this were pretty awesome), ping-pong ball  painted black, mini billiard number 8 ball (it is already black and you find it on eBay sold as a key chain) and ball bearings.
  • Lighting. I prefer halogen spotlights, IKEA mainly. I always avoid using Flash light to document art. Their CRI – color rendering index – is pretty low.
  • Software. Manuals and software on the RTI group’s website.
  • Metering tool. You need to put the lamp at the same distance while you move it around the object and at different angles.  I use Bosh DLE 40 laser rangefinder. It’s precise (1.5 mm), small and lightweight. It fits perfectly in one hand.
  • Remote shutter. As i said I work alone. don’t get me wrong. I’d love company but that would dramatically increase traveling cost and so on.
Reflectance Transformation Imaging, RTI, paintings authentication, Technical Art Examination

Reflectance Transformation Imaging tools. Spotlight, black spheres of different sizes, remote shutter, range finder. Yes, don’t forget billiard ball # 8. You always need some luck!

Let’s start! This video briefly describe the hardware and software process. It’s just a brief description all the details you need to know are on the CHI group website.

 

Infrared RTI. Yes, you read right. I did some Infrared RTI. It has some advantages. When it comes to infrared reflected, the better contrast to read the underdrawing can be achieved at different lighting angle  for different areas. So, for example bright areas have a different behavior than dark areas. See the shots below from an Infrared RTI I did on a mock-up painting with a underdrawing squaring grid. More details about this painting can be found here. It result that on bright areas the underdrawing grids are better visible in raking light while in the darker areas they are better seen in top lighting. Compared with the normal digital infrared image, it seems, Infrared RTI can give a better imaging of the underdrawing.

Infrared Reflectance Transformation Imaging

Infrared Reflectance Transformation Imaging. lighting from bottom left.

Infrared Reflectance Transformation Imaging 2

Infrared Reflectance Transformation Imaging. Lighting from top left.

Infrared Reflectance Transformation Imaging 3

Infrared Reflectance Transformation Imaging. Lighting from middle right.

Infrared Reflectance Transformation Imaging 4

Infrared Reflectance Transformation Imaging. Lighting from center.

Infrared Reflectance Transformation Imaging 5

Infrared Reflectance Transformation Imaging. Lighting from top left.

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2016-10-17T16:35:16+00:00

32 Comments

  1. cantorsusanSusan Roberts-Manganelli December 3, 2012 at 4:33 pm - Reply

    Thanks Antonio. We hope to try RTI on a Greek pot. Have you ever worked on objects with it? And can you please credit your musical background? I Solisti Veneti perhaps?

    • Antonino Cosentino December 3, 2012 at 9:13 pm - Reply

      Hi Susan, thanks for your appreciation of my blog! I’m actually doing RTI only on paintings but you should not any problems on 3D objects. I would just try to have as much depth of field as possible, closing aperture a couple of stops from the smallest (to avoid diffraction). And use lots of lighting. Then it depends if you want document just a small (almost flat detail) or all the crater.
      Music credit is: Advent_Chamber_Orchestra, Handel, Entrance_to_the_Queen_of_Sheba_for_Two_Oboes_Strings_and_Continuo_allegro. For my videos I find inspiration using and browsing free music from this awesome site freemusicarchive.org Ciao Susan!

  2. Moshe Caine December 7, 2012 at 8:13 am - Reply

    RTI on 3D objects like pots, Cuneiform tablets, etc is, possibly, even more impressive than in paintings. The ability to infinitely relight the object from endless angles, intensities and filters, really brings out the 3D information.
    Like Antonio says, it is essential to controll depth of field. Closing down the aperture is essential. Obviously, the smaller the object, the closer the distance. The closer the distance, the smaller the depth of field. A very sturdy tripod too is essential.
    Here is a link to a few examples of my work:
    http://www.zupdom.com/moshecaine/research/research_rti/rti.html

    If you intend to shoot many small pottery objects I would highly suggest constructing an RTI dome. You can find lots of info on the topic online.

    • Antonino Cosentino December 7, 2012 at 8:23 am - Reply

      I’m very glad this blog is becoming an active forum to share useful tips and tricks among professionals of different backgrounds!

  3. Moshe Caine December 7, 2012 at 8:25 am - Reply

    Antonio. I have also done some experimentation on combined RTI and infrared, on some fragments of the Dead Sea Scrolls, together with a colleague of mine, Michael Magen, head of paper conservation at the Israel Museum. Due however to the sensitivity, both of the actual fragments and no less to the highly explosive topic, we were not able to full complete the investigative process. The results, however, we’re very encouraging. The IR enabled to clearly view the texts hidden beneath the dark encrusted top layer, while the RTI enabled to clearly examine the surface of the parchment.
    Here is a video of a similar experiment carried out on an illuminated manuscript at the museum.
    http://www.zupdom.com/moshecaine/research/research_rti/research_rti/hagaddah.html

    • Antonino Cosentino December 7, 2012 at 8:43 am - Reply

      I also could appreciate on your website your portfolio of artistic photography!

  4. Moshe Caine December 7, 2012 at 5:32 pm - Reply

    We have also done some micro RTI work, using a Dinolite as our imaging source.
    For a micro black ball we used a ball fom a ball point pen, painted black.
    The light source was a small LED penlight torch.
    It works!

  5. John Anderson January 14, 2013 at 10:11 pm - Reply

    Hi, everyone. I’ve just discovered this technique on the web.So far, I haven’t gone beyond exploring the software and transforming some sample images, but I’m impressed! I’ll be using the technique for exploring surfaces of materials, and I hope to include some images. in the very near future. Best wishes, John Anderson, Ireland.

  6. John Anderson February 15, 2013 at 9:34 pm - Reply

    Hi, again. I’ve had good results with a variety of test subjects, but have a question. I capture my stack with a hi-res camera (Canon 5D2) and Zeiss macro lens. I convert RAW to DNG/TIFF. So far, I have high-resolution images. Then, peversely, I have to convert my high-res images to JPEGS, losing most if not all image high-freqency detail in the process!

    What is going on?

    Why not simply use DNG files and preserve detail? I can’t ask this question of CHI because their ‘forum’ won’t allow me to register. Anyone?

    Kind regards,

    John Anderson.

    • Antonino Cosentino February 18, 2013 at 10:36 pm - Reply

      Hi john,
      hope somebody at CHI see your comment. though, I guess it would be a bit too much for a PC to handle big DNG files in order to make the RTI file.

      • John Anderson February 28, 2013 at 6:02 pm - Reply

        Thanks, Antonio. It’s a pity, because jpeg compression causes considerable loss of fine detail and, after all, PCs are becoming faster and cheaper every year!

        Kind regards,

        John Anderson.

        • Antonino Cosentino February 28, 2013 at 8:19 pm - Reply

          Well, let me know if you get any answer about it. I just had to buy a new PC. My just 1-year old PC was not enough for the imaging I’m doing now.

  7. John Anderson March 2, 2013 at 4:01 pm - Reply

    Thanks, Antonio, I did receive a reply. There are no plans to extend capture to hi-res images. Great pity.

    We are using a Dell workstation to process RTIs. We’ve installed 128GB RAM; that, and fast dual-Zeon processors runs through a 40-image jpeg stack (dumbed down from Canon 5D2 RAW files) in under 60-seconds. Just enough time to pour a coffee!

    I’ll post some of our forensic RTI images soon on Flickr.

    Regards,

    John.

    • Antonino Cosentino March 2, 2013 at 10:36 pm - Reply

      I actually read that reply since I was on the RTI forum to post my own question. How to run RTI viewer and builder on Windows 8?? I just switched to this operative system and they don’t work. 120 GB Ram..wel you definitively have much more computational power! I just switched from 8GB to 16 GB and I thought it was a great improvement! But 120GB, that’s a lot… ahah

      • John Anderson March 4, 2013 at 1:04 pm - Reply

        Hi, Antonio. It’s well worth the expense of populating your PC with as much RAM as possible. (It’s inexpensive these days). Otherwise the CPU will use the hard disk, and that quickly slows down computations. In addition, two hard drives should be fitted (again, cheap); one for program storage, the other a scratch disk to hold your images. It makes all the difference! By the way, you didn’t say what make of PC you bought? As for Windows 8……

        Regard,

        John.

  8. John Anderson March 4, 2013 at 1:56 pm - Reply

    Antonio, You say RTI won’t run on your Windows 8 platform. RTI is written in the high-level Java language, and should run on most machines with JAVA 6 or later installed. As for Windows 8, it is an unmitigated disaster, far worse than Millenium or Vista. Microsoft no longer seem to care about professional users; I suspect Windows 8 is designed for idiots!

    However, there may be a compatibility mode available, which allows you to run software designed for windows XP/7. Alternatively, if you can find a techie with an OEM XP disk, he can reformat the drive and load that instead.

    Let me know how you get on.

    Regards,

    John.

    • Antonino Cosentino March 5, 2013 at 4:50 pm - Reply

      Hi John, thank you so much for your hints on Win8. I should have heard from you before I did switch to Win 8!!! Anyway, unexpectedly I manage to get the builder working just by re-installing the Java machine. But still the Viewer shows a flat red screen in the RTI window. I posted about this problem to the RTI forum, I’ll see what they’ll say. This is a problem other unlucky Win 8 users are going to have.
      John, let me know if you publish anything of your RTI works. I am really interested to see. For the little I understand you work in a forensic company? I’ll be interested to know other applications of RTI in forensic that would match art examination. I used RTI for documenting signs and incisions in the ground.

      • John Anderson March 5, 2013 at 6:55 pm - Reply

        Hi Antonio, go to the link I posted, you may find the fix works; otherwise, you’ll have to try and find someone (are you in the ‘States or in Europe?) to install windows XP Pro for you. It isn’t that difficult – I’m aware of many professional users in Britain, and here in Ireland, who are experiencing major problems with Windows 8, and are reinstalling XP or 7. Microsoft sucks.

        I’m a materials scientist and principal of a small company carrying out a variety of investigations on polymers, documents, wood, etc. for the legal and insurance professions. Much of our our work involves chemical and instrumental analysis. We’re currently still evaluating RTI (but curse the jpeg-only format!) I’ll be posting the results of our endeavours as soon as possible.

        Let me know how you get on.

        Kind regards,
        John

        Now you’ve reminded me, I must send a donation to CHI.

        • Antonino Cosentino March 6, 2013 at 5:28 pm - Reply

          Hi John , thanks again for your tips. I can install Win 7, no problem. I’m in Italy now, running my start up technical art examination service. let me know when you post something. Ciao

  9. John Anderson March 4, 2013 at 2:01 pm - Reply
  10. John Anderson March 15, 2013 at 3:11 pm - Reply

    Hi, Antonio, sorry for the delay posting RTI images to Flickr. There are major problems currently with that site. Yahoo say they’re fixing it. As soon as I can post I’ll let you know.

    I’m pleased to hear you resolved your PC problem by reinstalling Win 7. Interestingly, there is so much anger at Microsoft’s Win 8 rubbish, DELL are offering WIN 7 as an alternative OS for their machines.

    Best wishes, John Anderson.

  11. John Anderson March 17, 2013 at 5:29 pm - Reply

    Hello Antonio. My colleague Tony Kavanagh (he’s the Flickr expert) has kindly set up a Flickr group called Forensic RTI Imaging. The web address is

    http://www.flickr.com/groups/2167393@N20/

    We’ve started by posting a humerous image. Do you think you could carry that around with you!

    Please feel free to post images and discussions. We’ll be posting more (serious stuff!) in early course.

    Kind regards,

    John.

    • Antonino Cosentino March 17, 2013 at 7:49 pm - Reply

      Hi John, i just signed to the group. Yeah, that’s the largest RTI sphere ever!! ahaha

      On Sun, Mar 17, 2013 at 5:29 PM, Cultural Heritage Science Open Source

  12. Wany Ri May 24, 2013 at 9:29 pm - Reply

    Hi. I am working on a master’s degree in Art-history. Especially i am interested in restoration of artifacts through the RTI method. It is so imformative to me 🙂

  13. mohamed abdel rahman September 19, 2014 at 12:00 am - Reply

    i am conservator i would use Reflectance Transformation Imaging (RTI) System for carbonized papyri
    could you provide me some tips and tricks IRRTI
    thank

    • Antonino Cosentino September 19, 2014 at 11:33 am - Reply

      Hi Mohamed,
      sure, I’m happy to help you. What you need to know specifically? have you done RTI already?

  14. Ayman Yaghi January 23, 2017 at 8:11 pm - Reply

    hello Antonio, Ive read what u have achieved ,, its really a great job , i appreciate what u have reached and I would like to ask if u have did RTI with UV Reflection !!

    • Antonino Cosentino January 23, 2017 at 10:32 pm - Reply

      Hi Ayman,
      thanks for your appreciation. I didn’t do RTI with UV radiation but I recall some other professionals did and used it for detecting incisions in transparent materials such as glass and crystals.

  15. Albert September 11, 2017 at 11:12 pm - Reply

    buenas tardes Antonio, recien me esoy iniciando el el tema, sono una duda me instale el programa y cuando termino de procesar me sale error Pach HSH

    • Antonino Cosentino September 12, 2017 at 10:09 am - Reply

      Hi Albert, the issue could be due to a number of facts. Try to install on a different computer with another operative system.

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